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{{Short description|Extinct migratory pigeon previously endemic to North America}}
{{About||the 2010 mumblecore film|Passenger Pigeons (film){{!}}''Passenger Pigeons'' (film)}}
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{{Use mdy dates|date=July 2019}}
{{Speciesbox
| fossil_range= {{Geological range|5.33|0}} [[Zanclean]]–[[Holocene]]<ref>{{cite web |title=†Ectopistes Swainson 1827 (passenger pigeon) |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=67689&is_real_user=1 |website=PBDB}}</ref>
| name = Passenger pigeon
| image = Bird lore (1913) (14562557107).jpg
| image_caption = Live female in 1898, kept in the [[aviary]] of [[Charles Otis Whitman|C. O. Whitman]]
| status = EX
| status_system = IUCN3.1
| status_ref =<ref name="iucn status 19 November 2021">{{cite IUCN |author=BirdLife International |title=''Ectopistes migratorius'' |date=2019 |volume=2019 |article-number=e.T22690733A152593137 |doi=10.2305/IUCN.UK.2019-3.RLTS.T22690733A152593137.en |access-date=19 November 2021}}</ref>
| status2 = GX
| status2_system = TNC
| status2_ref = <ref>{{cite web |title=''Ectopistes migratorius''. NatureServe Explorer 2.0 |url=https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.104865/Ectopistes_migratorius|website=explorer.natureserve.org |access-date=31 March 2022}}</ref>
| extinct = 1914
| genus = Ectopistes
| parent_authority = [[William Swainson|Swainson]], 1827
| species = migratorius
| authority = ([[Carl Linnaeus|Linnaeus]], 1766)
| synonyms =
* ''Columba migratoria'' <small>Linnaeus, 1766</small>
* ''Columba canadensis'' <small>Linnaeus, 1766</small>
* ''Ectopistes migratoria'' <small>Swainson, 1827</small>
| range_map = Map-Ectopistes-migratorius.png
| range_map_caption = Distribution map, with former range in orange and breeding zone in red
}}

The '''passenger pigeon''' or '''wild pigeon''' ('''''Ectopistes migratorius''''') is an [[bird extinction|extinct species]] of [[Columbidae|pigeon]] that was [[endemic]] to [[North America]]. Its common name is derived from the French word ''passager'', meaning "passing by", due to the migratory habits of the species. The scientific name also refers to its migratory characteristics. The morphologically similar [[mourning dove]] (''Zenaida macroura'') was long thought to be its closest relative, and the two were at times confused, but genetic analysis has shown that the genus ''[[Patagioenas]]'' is more closely related to it than the [[Zenaida doves|''Zenaida'' doves]].

The passenger pigeon was [[sexually dimorphic]] in size and coloration. The male was {{convert|390|to|410|mm|in|abbr=on|1}} in length, mainly gray on the upperparts, lighter on the underparts, with [[iridescent]] bronze feathers on the neck, and black spots on the wings. The female was {{convert|380 to 400|mm|in|abbr=on|1}}, and was duller and browner than the male overall. The juvenile was similar to the female, but without iridescence. It mainly inhabited the [[deciduous forests]] of [[Eastern United States|eastern North America]] and was also recorded elsewhere, but bred primarily around the [[Great Lakes]]. The pigeon migrated in enormous flocks, constantly searching for food, shelter, and breeding grounds, and was once the most abundant bird in North America, numbering around 3 billion, and possibly up to 5 billion. A very fast flyer, the passenger pigeon could reach a speed of {{convert|100|km/h|mph|abbr=on}}. The bird fed mainly on [[mast seeding|mast]], and also fruits and invertebrates. It practiced [[communal roosting]] and [[communal breeding]], and its extreme gregariousness may have been linked with searching for food and [[predator satiation]].

Passenger pigeons were hunted by Native Americans, but hunting intensified after the arrival of Europeans, particularly in the 19th century. Pigeon meat was commercialized as cheap food, resulting in [[hunting]] on a massive scale for many decades. There were several other factors contributing to the decline and subsequent extinction of the species, including shrinking of the large breeding populations necessary for preservation of the species and widespread [[deforestation]], which destroyed its [[habitat]]. A slow decline between about 1800 and 1870 was followed by a rapid decline between 1870 and 1890. In 1900, the last confirmed wild bird was shot in southern Ohio.<ref name="iucn status 19 November 2021"/><ref>{{cite journal |last=Henninger |first=W. F. |title=A Preliminary List of the Birds of Middle Southern Ohio |date=1902 |journal=The Wilson Bulletin |volume=14 |issue=3 |pages=77–93 |jstor=4153807 |issn=0043-5643 }}</ref> The last captive birds were divided in three groups around the turn of the 20th century, some of which were photographed alive. [[Martha (passenger pigeon)|Martha]], thought to be the last passenger pigeon, died on September 1, 1914, at the [[Cincinnati Zoo and Botanical Garden|Cincinnati Zoo]]. The eradication of the species is a notable example of [[Holocene extinction|anthropogenic extinction]].

==Taxonomy==
[[File:Pigeon-of-passage.jpg|thumb|left|Earliest published illustration of the species (a male), [[Mark Catesby]], 1731]]
Swedish naturalist [[Carl Linnaeus]] coined the binomial name ''[[Columba (genus)|Columba]] macroura'' for both the [[mourning dove]] and the passenger pigeon in the 1758 edition of his work ''[[Systema Naturae]]'' (the starting point of [[biological nomenclature]]), wherein he appears to have considered the two identical. This composite description cited accounts of these birds in two pre-Linnean books. One of these was [[Mark Catesby]]'s description of the passenger pigeon, which was published in his 1731 to 1743 work ''Natural History of Carolina, Florida and the Bahama Islands'', which referred to this bird as ''Palumbus migratorius'', and was accompanied by the earliest published illustration of the species. Catesby's description was combined with the 1743 description of the mourning dove by [[George Edwards (naturalist)|George Edwards]], who used the name ''C.&nbsp;macroura'' for that bird. There is nothing to suggest Linnaeus ever saw specimens of these birds himself, and his description is thought to be fully derivative of these earlier accounts and their illustrations. In his 1766 edition of ''Systema Naturae'', Linnaeus dropped the name ''C.&nbsp;macroura'', and instead used the name ''C.&nbsp;migratoria'' for the passenger pigeon, and ''C.&nbsp;carolinensis'' for the mourning dove.<ref>{{cite book |last1=Catesby |first1=M. |title=Natural History of Carolina, Florida and the Bahama Islands |year=1729 |location=London |volume=1 |publisher=W. Innys and R. Manby |page=23 |url=https://archive.org/stream/naturalhistoryCC1V1Cate#page/n137/mode/2up}}</ref><ref name="Mourning Dove 1993">{{cite book |last1=Aldrich |first1=J. W. |year=1993 |page=48 |chapter=Classification and Distribution |title=Ecology and management of the Mourning Dove |editor=Baskett, T.S. |editor2=Sayre, M.W. |editor3=Tomlinson, R.E. |editor4=Mirarchi, R.E. |publisher=[[Stackpole Books]] |isbn=978-0-8117-1940-7 |location=Harrisburg, PA}}</ref><ref name="Hemming 1952">{{cite journal |last=Hemming |first=F. |title=Proposed use of the plenary powers to secure that the name ''Columba migratoria'' Linnaeus, 1766, shall be the oldest available name for the Passenger Pigeon, the type species of the genus ''Ectopistes'' Swainson, 1827 |journal=[[Bulletin of Zoological Nomenclature]] |volume=9 |pages=80–84 |year=1952 |doi=10.5962/bhl.part.10238 |doi-access=free |url=https://www.biodiversitylibrary.org/page/12158465#page/152/mode/1up}}</ref> In the same edition, Linnaeus also named ''C.&nbsp;canadensis'', based on ''Turtur canadensis'', as used by [[Mathurin Jacques Brisson]] in 1760. Brisson's description was later shown to have been based on a female passenger pigeon.<ref name="Oberholser 1918"/>

In 1827, [[William Swainson]] moved the passenger pigeon from the genus ''Columba'' to the new [[monotypic]] genus ''Ectopistes'', due in part to the length of the wings and the wedge shape of the tail.<ref>{{cite journal |last=Swainson |first=W. |title=Mr. Swainson on several new groups in Ornithology |journal=[[The Zoological Journal]] |volume=3 |page=362 |year=1827 |url=https://archive.org/stream/zoologicaljourna03lond#page/362/mode/2up}}</ref> In 1906 [[Outram Bangs]] suggested that because Linnaeus had wholly copied Catesby's text when coining ''C.&nbsp;macroura'', this name should apply to the passenger pigeon, as ''E.&nbsp;macroura''.<ref>{{cite journal |last=Bangs |first=O. |title=The names of the passenger pigeon and the mourning dove |journal=[[Proceedings of the Biological Society of Washington]] |volume=19 |pages=43{{ndash}}44 |year=1906 |url=https://www.biodiversitylibrary.org/page/2348105#page/67/mode/1up}}</ref> In 1918 [[Harry C. Oberholser]] suggested that ''C.&nbsp;canadensis'' should take precedence over ''C.&nbsp;migratoria'' (as ''E.&nbsp;canadensis''), as it appeared on an earlier page in Linnaeus' book.<ref name="Oberholser 1918">{{cite journal |last=Oberholser |first=H. C. |title=The scientific name of the Passenger Pigeon |journal=Science |volume=48 |issue=1244 |page=445 |year=1918 |bibcode=1918Sci....48..445O |pmid=17752099 |doi=10.1126/science.48.1244.445 |s2cid=28529631 |url=https://archive.org/stream/jstor-1641492/1641492#page/n1/mode/2up}}</ref> In 1952 [[Francis Hemming]] proposed that the [[International Commission on Zoological Nomenclature]] (ICZN) secure the specific name ''macroura'' for the mourning dove, and the name ''migratorius'' for the passenger pigeon, since this was the intended use by the authors on whose work Linnaeus had based his description.<ref name="Hemming 1952"/> This was accepted by the ICZN, which used its [[plenary powers]] to designate the species for the respective names in 1955.<ref>{{cite book |last1=Schenk |first1=E. T. |last2=McMasters |first2=J. H. |year=1956 |page=89 |title=Procedure in Taxonomy |edition=Third |publisher=[[Stanford University Press]] |isbn=978-0-8047-3867-5 |location=Stanford, California}}</ref>

===Evolution===
[[File:Ectopistes migratorius (passenger pigeon).jpg|thumb|Mounted male passenger pigeon, [[Field Museum of Natural History]]]]
[[File:Patagioenas fasciata -San Luis Obispo, California, USA-8 (1).jpg|thumb|[[Band-tailed pigeon]], a species in the related genus ''[[Patagioenas ]]'']]
[[File:Zenaida macroura -California-8-2c.jpg|thumb|The physically similar [[mourning dove]] is not closely related.]]
The passenger pigeon was a member of the pigeon and dove family, [[Columbidae]]. The oldest known fossil of the genus is an isolated humerus (USNM 430960) known from the Lee Creek Mine in North Carolina in sediments belonging to the [[Yorktown Formation]], dating to the [[Zanclean]] stage of the [[Pliocene]], between 5.3 and 3.6 million years ago.<ref>{{cite journal |last1=Ray |first1=Clayton E. |last2=Bohaska |first2=David J. |title=Miocene and Pliocene birds from the Lee Creek Mine, North Carolina in Geology and Paleontology of the Lee Creek Mine, North Carolina, III |date=2001 |journal=Smithsonian Contributions to Paleobiology |volume=90 |language=en |issue=90 |pages=299–300 |doi=10.5479/si.00810266.90.1 |hdl=10088/2006 |url=https://repository.si.edu/handle/10088/2006}}</ref> Its closest living relatives were long thought to be the [[Zenaida doves|''Zenaida'' doves]], based on morphological grounds, particularly the physically similar mourning dove (now ''Z.&nbsp;macroura'').<ref name="Blockstein 4"/><ref>{{cite conference |last=Miller |first=W. J. |title=The Biology and Natural History of the Mourning Dove |book-title=Should Doves be Hunted in Iowa? |publisher=Ames [[Audubon Society]] |date=January 16, 1969 |location=Ames, IA |url=http://www.ringneckdove.com/Wilmer's%20WebPage/mourning__doves.htm |access-date=April 23, 2013 |archive-url=https://web.archive.org/web/20120920051011/http://www.ringneckdove.com/Wilmer%27s%20WebPage/mourning__doves.htm |archive-date=September 20, 2012}}</ref> It was even suggested that the mourning dove belonged to the genus ''Ectopistes'' and was listed as ''E.&nbsp;carolinensis'' by some authors, including [[Thomas Mayo Brewer]].<ref name="Brewer 717">{{cite book |last=Brewer |first=T. M. |author-link=Thomas Mayo Brewer |title=Wilson's American Ornithology: with Notes by Jardine; to which is Added a Synopsis of American Birds, Including those Described by Bonaparte, Audubon, Nuttall, and Richardson |publisher=Otis, Broaders, and Company |year=1840 |location=Boston |page=[https://archive.org/details/wilsonsamericano00wils/page/717 717] |url=https://archive.org/details/wilsonsamericano00wils}}</ref> The passenger pigeon was supposedly descended from ''Zenaida'' pigeons that had adapted to the woodlands on the plains of central North America.<ref name="Extinct Birds"/>

The passenger pigeon differed from the species in the genus ''Zenaida'' in being larger, lacking a facial stripe, being [[sexually dimorphic]], and having [[iridescent]] neck feathers and a smaller [[clutch (eggs)|clutch]]. In a 2002 study by American geneticist [[Beth Shapiro]] et al., museum specimens of the passenger pigeon were included in an [[ancient DNA]] analysis for the first time (in a paper focusing mainly on the [[dodo]]), and it was found to be the [[sister taxon]] of the cuckoo-dove genus ''[[Macropygia]]''. The ''Zenaida'' doves were instead shown to be related to the quail-doves of the genus ''[[Geotrygon]]'' and the ''[[Leptotila]]'' doves.<ref>{{cite journal |last1=Shapiro |first1=B. |last2=Sibthorpe |first2=D. |last3=Rambaut |first3=A. |last4=Austin |first4=J. |last5=Wragg |first5=G. M. |last6=Bininda-Emonds |first6=O. R. P. |last7=Lee |first7=P. L. M. |last8=Cooper |first8=A. |year=2002 |title=Flight of the Dodo |journal=Science |volume=295 |issue=5560 |page=1683 |doi=10.1126/science.295.5560.1683 |pmid=11872833 |ref={{sfnRef |Shapiro et al. |2002 |pmid=11872833 |doi=10.1126/science.295.5560.1683 |url=https://pgl.soe.ucsc.edu/dodo_Shapiro02.pdf}}}}</ref><ref name="Fulton"/><ref name=Johnson/>

A more extensive 2010 study instead showed that the passenger pigeon was most closely related to the New World ''[[Patagioenas]]'' pigeons, including the [[band-tailed pigeon]] (''P.&nbsp;fasciata'') of western North America, which are related to the Southeast Asian species in the genera ''[[Turacoena]]'', ''Macropygia'', and ''[[Reinwardtoena]]''. This [[clade]] is also related to the ''Columba'' and ''[[Streptopelia]]'' doves of the Old World (collectively termed the "typical pigeons and doves"). The authors of the study suggested that the ancestors of the passenger pigeon may have colonized the New World from South East Asia by flying across the [[Pacific Ocean]], or perhaps across [[Beringia]] in the north.<ref name=Johnson>{{cite journal |last=Johnson |first=K. P. |author2=Clayton, D. H. |author3=Dumbacher, J. P. |author4=Fleischer, R. C. |title=The flight of the Passenger Pigeon: phylogenetics and biogeographic history of an extinct species |journal=Molecular Phylogenetics and Evolution |volume=57 |issue=1 |pages=455–8 |year=2010 |bibcode=2010MolPE..57..455J |pmid=20478386 |doi=10.1016/j.ympev.2010.05.010}}</ref>

In a 2012 study, the [[nuclear DNA]] of the passenger pigeon was analyzed for the first time, and its relationship with the ''Patagioenas'' pigeon was confirmed. In contrast to the 2010 study, these authors suggested that their results could indicate that the ancestors of the passenger pigeon and its Old World relatives may have originated in the [[Neotropical region]] of the New World.<ref name="Fulton">{{cite journal |last=Fulton |first=T. L. |author2=Wagner, S. M. |author3=Fisher, C. |author4=Shapiro, B. |title=Nuclear DNA from the Extinct Passenger Pigeon (''Ectopistes migratorius'') Confirms a Single Origin of New World Pigeons |journal=[[Annals of Anatomy]] |volume=194 |issue=1 |pages=52–7 |year=2012 |bibcode=2012AnAAA.194...52F |pmid=21482085 |doi=10.1016/j.aanat.2011.02.017}}</ref>

The [[cladogram]] below follows the 2012 DNA study showing the position of the passenger pigeon among its closest relatives:<ref name="Fulton"/>
{{clade |style=font-size:100%; line-height:100%
|1={{clade
 |1={{clade
  |1={{clade
   |1={{clade
    |1={{clade
     |1=''[[Macropygia]]'' (cuckoo-doves)
     |2=''[[Reinwardtoena]]''}}
   |2=''[[Turacoena]]''}}
  |2={{clade
   |1=''[[Columba (genus)|Columba]]'' (Old World pigeons)
   |2=''[[Streptopelia]]'' (turtle doves and collared doves)}}}}
 |2={{clade
  |1=''[[Patagioenas]]'' (New World pigeons)
  |2='''''Ectopistes''''' ('''passenger pigeon''')}}}}}}}}

DNA in old museum specimens is often degraded and fragmentary, and passenger pigeon specimens have been used in various studies to discover improved methods of analyzing and assembling genomes from such material. DNA samples are often taken from the toe pads of bird skins in museums, as this can be done without causing significant damage to valuable specimens.<ref>{{cite book |chapter=Case Study: Recovery of Ancient Nuclear DNA from Toe Pads of the Extinct Passenger Pigeon |title=Ancient DNA |volume=840 |pages=29–35 |series=Methods in Molecular Biology |year=2012 |last1=Fulton |first1=T. L. |last2=Wagner |first2=S. M. |last3=Shapiro |first3=B. |isbn=978-1-61779-515-2 |pmid=22237518 |doi=10.1007/978-1-61779-516-9_4}}</ref><ref>{{cite journal |title=The De Novo Assembly of Mitochondrial Genomes of the Extinct Passenger Pigeon (''Ectopistes migratorius'') with Next Generation Sequencing |journal=[[PLOS One]] |volume=8 |issue=2 |article-number=e56301 |year=2013 |last1=Hung |first1=C. M. |last2=Lin |first2=R. C. |last3=Chu |first3=J. H. |last4=Yeh |first4=C. F. |last5=Yao |first5=C. J. |last6=Li |first6=S. H. |bibcode=2013PLoSO...856301H |pmid=23437111 |doi=10.1371/journal.pone.0056301 |doi-access=free |pmc=3577829}}</ref> The passenger pigeon had no known subspecies.<ref name="Blockstein 4">{{Harvnb|Blockstein|2002|p=4}}</ref> [[Hybrid (biology)|Hybridization]] occurred between the passenger pigeon and the [[Barbary dove]] (''Streptopelia risoria'') in the aviary of [[Charles Otis Whitman]] (who owned many of the last captive birds around the turn of the 20th century, and kept them with other pigeon species) but the offspring were infertile.<ref name="Extinct Birds">{{cite book |last1=Hume |first1=J. P. |author-link=Julian Pender Hume |last2=Walters |first2=M. |title=Extinct Birds |publisher=T & AD Poyser |year=2012 |location=London |isbn=978-1-4081-5725-1 |pages=144{{ndash}}146}}</ref><ref>{{cite journal |jstor=4070695 |last=Deane |first=R. |title=The Passenger Pigeon (Ectopistes migratorius) in Confinement |journal=The Auk |volume=25 |issue=2 |pages=181–183 |year=1908 |doi=10.2307/4070695 |url=https://archive.org/stream/jstor-4070695/4070695#page/n1/mode/2up}}</ref>

===Etymology===
The genus name, ''Ectopistes'', translates as "moving about" or "wandering", while the specific name, ''migratorius'', indicates its [[bird migration|migratory]] habits.<ref name="Atkinson">{{cite book |last=Atkinson |first=G. E. |title=The Passenger Pigeon |editor=Mershon, W. B |publisher=The Outing Publishing Co |location=New York |year=1907 |page=188 |url=https://en.wikisource.org/wiki/Page:The_Passenger_Pigeon_-_Mershon.djvu/221}}</ref> The full binomial can thus be translated as "migratory wanderer". The English common name "passenger pigeon" derives from the French word ''{{lang|fr|passager}}'', which means "to pass by" in a fleeting manner.<ref name="Fuller 2014 30–47"/><ref>{{cite web |last=Harper |first=D. |title=Passenger (n.) |website=Online Etymology Dictionary |year=2012 |url=https://www.etymonline.com/word/passenger |access-date=April 23, 2013}}</ref> While the pigeon was extant, the name "passenger pigeon" was used interchangeably with "wild pigeon".<ref name="Schorger251">{{cite book |last1=Schorger |first1=A. W. |author-link=Arlie W. Schorger |title=The Passenger Pigeon: Its Natural History and Extinction |publisher=[[University of Wisconsin Press]] |year=1955 |location=Madison, WI |isbn=978-1-930665-96-5}} p. 251.<!--Please keep page number outside the cite template so that sfns with other page numbers can use the full citation. --></ref> The bird also gained some less-frequently used names, including blue pigeon, merne rouck pigeon, wandering long-tailed dove, and wood pigeon. In the 18th century, the passenger pigeon was known as ''tourte'' in [[New France]] (in modern Canada), but to the French in Europe it was known as ''tourtre''. In modern French, the bird is known as ''tourte voyageuse'' or ''pigeon migrateur'', among other names.<ref name="Schorger2523">{{Harvnb|Schorger|1955|pp=252–253}}</ref>

In the Native American [[Algonquian languages]], the pigeon was called ''amimi'' by the [[Lenape language|Lenape]], ''{{lang|oj|omiimii}}'' by the [[Anishinaabe language|Ojibwe]], and ''{{lang|mia|mimia}}'' by the [[Kaskaskia]] [[Miami-Illinois language|Illinois]].<ref>{{cite web |last=Tatum |first=J. |author2=Rementer, J. |author3=the Culture Preservation Committee |title=Extinct Birds the Lenape Knew |website=Culture and History of the Delaware Tribe |publisher=[[Delaware Tribe of Indians]] |year=2010 |url=https://delawaretribe.org/blog/2013/06/27/extinct-birds-the-lenape-knew/ |access-date=October 8, 2024 |archive-url=https://web.archive.org/web/20121006163804/http://culture.delawaretribe.org/extinctbirds.htm |archive-date=October 6, 2012}}</ref><ref>{{cite web |title=Omiimii |website=Ojibwe People's Dictionary |publisher=Department of American Indian Studies, [[University of Minnesota]] |url=https://ojibwe.lib.umn.edu/main-entry/omiimii-na |access-date=March 2, 2012}}</ref><ref name="Costa">{{cite web |last1=Costa |first1=D. J. |title=The St. Jérôme Dictionary of Miami-Illinois |website=Papers of the 36th Algonquian Conference |editor-first=H. C. |editor-last=Wolfart |location=Winnipeg |publisher=[[University of Manitoba]] |year=2005 |pages=107{{ndash}}133 |url=http://myaamiacenter.org/MCResources/costa_biblio/st_jerome_dictionary_costa.pdf |access-date=April 23, 2013 |archive-url=https://web.archive.org/web/20160611143937/http://myaamiacenter.org/MCResources/costa_biblio/st_jerome_dictionary_costa.pdf |archive-date=June 11, 2016}}</ref> Other names in [[Indigenous peoples of the Americas|indigenous American]] languages include ''{{lang|moh|ori'te}}'' in [[Mohawk language|Mohawk]], and ''{{lang|cho|putchee nashoba}}'', or "lost dove", in [[Choctaw language|Choctaw]].<ref name="Schorger255">{{Harvnb|Schorger|1955|p=255}}</ref> The [[Seneca people]] called the pigeon ''{{lang|see|jahgowa}}'', meaning "big bread", as it was a source of food for their tribes.<ref name="Fuller 2014 72–88"/> Chief [[Simon Pokagon]] of the [[Potawatomi]] stated that his people called the pigeon ''{{lang|pot|O-me-me-wog}}'', and that the Europeans did not adopt native names for the bird, as it reminded them of their domesticated pigeons, instead calling them "wild" pigeons, as they called the native peoples "wild" men.<ref name="Fuller 2014 150–161">{{Harvnb|Fuller|2014|pp=150–161}}</ref>

==Description==
[[File:Naturalis Biodiversity Center - RMNH.AVES.110090 - Ectopistes migratorius (Linnaeus, 1766) - Passenger Pigeon - specimen - video.webm|left|thumbtime=0:07|thumb|Turntable video of an adult male specimen at [[Naturalis Biodiversity Center]]]]

The passenger pigeon was [[sexually dimorphic]] in size and coloration. It weighed between {{convert|260|and|340|g|oz|abbr=on}}.<ref name="Blockstein 2"/> The adult male was about {{convert|390 to 410|mm|in|abbr=on|1}} in length.<ref name="Gibbs 319">{{cite book |last1=Gibbs |first1=D. |last2=Barnes |first2=E. |last3=Cox |first3=J. |title=Pigeons and Doves: A Guide to the Pigeons and Doves of the World |publisher=[[Pica Press]] |year=2001 |location=Sussex |isbn=978-1-873403-60-0 |pages=318{{ndash}}319}}</ref> It had a bluish-gray head, nape, and hindneck. On the sides of the neck and the upper mantle were iridescent display feathers that have variously been described as being a bright bronze, violet, or golden-green, depending on the angle of the light. The upper back and wings were a pale or slate gray tinged with olive brown, that turned into grayish-brown on the lower wings. The lower back and [[rump (animal)|rump]] were a dark blue-gray that became grayish-brown on the upper tail-[[covert feather]]s. The greater and median wing-covert feathers were pale gray, with a small number of irregular black spots near the end. The primary and secondary feathers of the wing were a blackish-brown with a narrow white edge on the outer side of the secondaries. The two central tail feathers were brownish gray, and the rest were white.<ref name="Fuller 2014 30–47"/><ref name="Gibbs 319"/>

The tail pattern was distinctive as it had white outer edges with blackish spots that were prominently displayed in flight.<ref name="Gibbs 319"/> The lower throat and breast were richly pinkish-[[rufous]], grading into a paler pink further down, and into white on the abdomen and undertail covert feathers. The undertail coverts also had a few black spots. The bill was black, while the feet and legs were a bright coral red. It had a [[carmine]]-red iris surrounded by a narrow purplish-red eye-ring.<ref name="Gibbs 319"/> The wing of the male measured {{convert|196 to 215|mm|in|abbr=on}}, the tail {{convert|175 to 210|mm|in|abbr=on}}, the bill {{convert|15 to 18|mm|in|abbr=on}}, and the [[tarsus (skeleton)|tarsus]] was {{convert|26 to 28|mm|in|abbr=on}}.<ref name="Fuller 2014 30–47"/>

[[File:Naturalis Biodiversity Center - RMNH.AVES.110091 - Ectopistes migratorius (Linnaeus, 1766) - Passenger Pigeon - specimen - video.webm|thumbtime=0:14|thumb|Turntable video of an adult female specimen at Naturalis]]

The adult female passenger pigeon was slightly smaller than the male at {{convert|380 to 400|mm|in|abbr=on|1}} in length. It was duller than the male overall, and was a grayish-brown on the forehead, crown, and nape down to the [[scapular]]s, and the feathers on the sides of the neck had less [[iridescence]] than those of the male. The lower throat and breast were a buff-gray that developed into white on the belly and undertail-coverts. It was browner on the upperparts and paler buff brown and less rufous on the underparts than the male. The wings, back, and tail were similar in appearance to those of the male except that the outer edges of the primary feathers were edged in buff or rufous buff.<ref name="Fuller 2014 30–47"/><ref name="Gibbs 319"/> The wings had more spotting than those of the male.<ref name="Blockstein 2"/> The tail was shorter than that of the male, and the legs and feet were a paler red. The iris was orange red, with a grayish blue, naked orbital ring. The wing of the female was {{convert|180 to 210|mm|in|abbr=on}}, the tail {{convert|150 to 200|mm|in|abbr=on}}, the bill {{convert|15 to 18|mm|in|abbr=on}}, and the tarsus was {{convert|25 to 28|mm|in|abbr=on}}.<ref name="Fuller 2014 30–47"/>

[[File:Naturalis Biodiversity Center - RMNH.AVES.110088 - Ectopistes migratorius (Linnaeus, 1766) - Passenger Pigeon - specimen - video.webm|left|thumbtime=0:07|thumb|Turntable video of a juvenile female specimen at Naturalis]]

The juvenile passenger pigeon was similar in [[plumage]] to the adult female, but lacked the spotting on the wings, and was a darker brownish-gray on the head, neck, and breast. The feathers on the wings had pale gray fringes (also described as white tips), giving it a scaled look. The secondaries were brownish-black with pale edges, and the [[tertial feathers]] had a rufous wash. The primaries were also edged with a rufous-brown color. The neck feathers had no iridescence. The legs and feet were dull red, and the iris was brownish, and surrounded by a narrow carmine ring.<ref name="Fuller 2014 30–47"/><ref name="Gibbs 319"/> The plumage of the sexes was similar during their first year.<ref name=Greenway/>

Of the hundreds of surviving skins, only one appears to be aberrant in color{{mdash}}an adult female from the collection of [[Walter Rothschild]], [[Natural History Museum at Tring]]. It is a washed brown on the upper parts, wing covert, secondary feathers, and tail (where it would otherwise have been gray), and white on the primary feathers and underparts. The normally black spots are brown, and it is pale gray on the head, lower back, and upper-tail covert feathers, yet the iridescence is unaffected. The brown [[mutation]] is a result of a reduction in [[eumelanin]], due to incomplete synthesis ([[oxidation]]) of this [[pigment]]. This sex-linked mutation is common in female wild birds, but it is thought the white feathers of this specimen are instead the result of bleaching due to exposure to sunlight.<ref name="Aberrant">{{cite journal |last1=Hume |first1=J. P. |last2=van Grouw |first2=H. |pages=168{{ndash}}193 |year=2014 |title=Colour aberrations in extinct and endangered birds |journal=[[Bulletin of the British Ornithologists' Club]] |volume=134}}</ref>

[[File:Passenger Pigeon skeleton.jpg|thumb|Skeleton of a male bird, 1914]]

The passenger pigeon was physically adapted for speed, endurance, and maneuverability in flight, and has been described as having a streamlined version of the typical pigeon shape, such as that of the generalized [[rock dove]] (''Columba livia''). The wings were very long and pointed, and measured {{convert|220|mm|in|abbr=on}} from the wing-chord to the primary feathers, and {{convert|120|mm|in|abbr=on}} to the secondaries. The tail, which accounted for much of its overall length, was long and wedge-shaped (or graduated), with two central feathers longer than the rest. The body was slender and narrow, and the head and neck were small.<ref name="Fuller 2014 30–47"/><ref name="SI">{{cite web |author=Department of Vertebrate Zoology, National Museum of Natural History |title=The Passenger Pigeon |website=Encyclopedia Smithsonian |publisher=[[Smithsonian Institution]] |date=March 2001 |url=https://www.si.edu/spotlight/passenger-pigeon |access-date=October 8, 2024}}</ref><ref name="Fuller 2014 162–168"/>

The internal anatomy of the passenger pigeon has rarely been described. [[Robert W. Shufeldt]] found little to differentiate the bird's [[osteology]] from that of other pigeons when examining a male skeleton in 1914, but [[Julian P. Hume]] noted several distinct features in a more detailed 2015 description. The pigeon's particularly large breast muscles indicated a powerful flight ([[musculus pectoralis major]] for downstroke and the smaller [[bird anatomy#Muscular system|musculus supracoracoideus]] for upstroke). The [[coracoid]] bone (which connects the [[scapula]], [[furcula]], and [[sternum]]) was large relative to the size of the bird, {{convert|33.4|mm|in|abbr=on}}, with straighter shafts and more robust articular ends than in other pigeons. The furcula had a sharper V-shape and was more robust, with expanded articular ends. The scapula was long, straight, and robust, and its [[distal]] end was enlarged. The sternum was very large and robust compared to that of other pigeons; its [[keel (bird anatomy)|keel]] was {{convert|25|mm|in|abbr=on}} deep. The overlapping [[uncinate processes of ribs|uncinate processes]], which stiffen the ribcage, were very well developed. The wing bones ([[humerus]], [[radius (bone)|radius]], [[ulna]], and [[carpometacarpus]]) were short but robust compared to other pigeons. The leg bones were similar to those of other pigeons.<ref name="Fuller 2014 162–168">{{Harvnb|Fuller|2014|pp=162–168}}</ref><ref>{{cite journal |jstor=4071953 |title=Osteology of the Passenger Pigeon (''Ectopistes migratorius'') |journal=[[The Auk]] |volume=31 |issue=3 |pages=358–362 |year=1914 |last1=Shufeldt |first1=R. W. |doi=10.2307/4071953 |url=https://www.biodiversitylibrary.org/part/86752}}</ref><ref name=Shufeldt>{{cite journal |jstor=4071611 |title=Anatomical and other notes on the Passenger Pigeon (''Ectopistes migratorius'') lately living in the Cincinnati Zoological Gardens |journal=The Auk |volume=32 |issue=1 |pages=29–41 |year=1915 |last1=Shufeldt |first1=R. W. |doi=10.2307/4071611 |url=https://www.biodiversitylibrary.org/page/15937222#page/87/mode/1up}}</ref>

===Vocalizations===
[[File:Passenger pigeon notes.jpg|thumb|[[Musical note]]s documenting male vocalizations, compiled by [[Wallace Craig]], 1911]]

The noise produced by flocks of passenger pigeons was described as deafening, audible for miles away, and the bird's voice as loud, harsh, and unmusical. It was also described by some as clucks, twittering, and cooing, and as a series of low notes, instead of an actual song. The birds apparently made croaking noises when building nests, and bell-like sounds when mating. During feeding, some individuals would give [[alarm calls]] when facing a threat, and the rest of the flock would join the sound while taking off.<ref name="Fuller 2014 30–47">{{cite book |last=Fuller |first=E. |author-link=Errol Fuller |title=The Passenger Pigeon |publisher=[[Princeton University Press]] |year=2014 |location=Princeton and Oxford |isbn=978-0-691-16295-9}} pp. 30–47.<!--Please keep page number(s) outside the cite template so that sfns with other page numbers can use the full citation. --></ref><ref name="Blockstein 8"/><ref name="Fuller 2001"/>

In 1911, American behavioral scientist [[Wallace Craig]] published an account of the gestures and sounds of this species as a series of descriptions and [[musical notation]]s, based on observation of C. O. Whitman's captive passenger pigeons in 1903. Craig compiled these records to assist in identifying potential survivors in the wild (as the physically similar mourning doves could otherwise be mistaken for passenger pigeons), while noting this "meager information" was likely all that would be left on the subject. According to Craig, one call was a simple harsh "keck" that could be given twice in succession with a pause in between. This was said to be used to attract the attention of another pigeon. Another call was a more frequent and variable scolding. This sound was described as "kee-kee-kee-kee" or "tete! tete! tete!", and was used to call either to its mate or towards other creatures it considered to be enemies. One variant of this call, described as a long, drawn-out "tweet", could be used to call down a flock of passenger pigeons passing overhead, which would then land in a nearby tree. "Keeho" was a soft cooing that, while followed by louder "keck" notes or scolding, was directed at the bird's mate. A nesting passenger pigeon would also give off a stream of at least eight mixed notes that were both high and low in tone and ended with "keeho". Overall, female passenger pigeons were quieter and called infrequently. Craig suggested that the loud, strident voice and "degenerated" musicality was the result of living in populous colonies where only the loudest sounds could be heard.<ref name="Blockstein 8"/><ref name="Craig 1911">{{cite journal |last=Craig |first=W. |title=The expressions of emotion in the pigeons. III. The Passenger Pigeon (''Ectopistes migratorius'' Linn.) |journal=The Auk |series=4 |volume=28 |issue=4 |pages=408–427 |year=1911 |jstor=4071160 |doi=10.2307/4071160 |url=https://archive.org/stream/jstor-4071160/4071160#page/n1/mode/2up}}</ref>

==Distribution and habitat==
[[File:Passenger Pigeon in flight.jpg|thumb|Specimen in flying pose, [[Academy of Natural Sciences of Drexel University]]]]

The passenger pigeon was found across most of North America east of the [[Rocky Mountains]], from the [[Great Plains]] to the [[East Coast of the United States|Atlantic coast]] in the east, to the south of Canada in the north, and the north of Mississippi in the southern United States, coinciding with its primary habitat, the eastern [[temperate deciduous forest|deciduous forests]]. Within this range, it constantly migrated in search of food and shelter. It is unclear if the birds favored particular trees and terrain, but they were possibly not restricted to one type, as long as their numbers could be supported.<ref name="Fuller 2014 30–47"/><ref name="Blockstein 2">{{Harvnb|Blockstein|2002|p=2}}</ref> It originally bred from the southern parts of eastern and central Canada south to eastern Kansas, Oklahoma, Mississippi, and Georgia in the United States, but the primary breeding range was in southern Ontario and the [[Great Lakes]] states south through states north of the [[Appalachian Mountains]].<ref name="Blockstein 3"/> Though the western forests were ecologically similar to those in the east, these were occupied by band-tailed pigeons, which may have kept out the passenger pigeons through [[competitive exclusion]].<ref name="Extinct Birds"/>

The passenger pigeon wintered from Arkansas, Tennessee, and North Carolina south to Texas, the Gulf Coast, and northern Florida, though flocks occasionally wintered as far north as southern Pennsylvania and Connecticut. It preferred to winter in large swamps, particularly those with [[alder]] trees; if swamps were not available, forested areas, particularly with [[pine]] trees, were favored roosting sites. There were also sightings of passenger pigeons outside of its normal range, including in several Western states, [[Bermuda]], [[Cuba]], and [[Mexico]], particularly during severe winters.<ref name="Blockstein 3"/><ref name="Blockstein 5">{{Harvnb|Blockstein|2002|p=5}}</ref><ref name="Blockstein 6"/> It has been suggested that some of these extralimital records may have been due to the paucity of observers rather than the actual extent of passenger pigeons; North America was then unsettled country, and the bird may have appeared anywhere on the continent except for the far west.<ref name="Blockstein 2"/> There were also records of stragglers in Scotland, Ireland, and France, although these birds may have been escaped captives, or the records incorrect.<ref name="Fuller 2014 30–47"/><ref name="Blockstein 3">{{Harvnb|Blockstein|2002|p=3}}</ref>

More than 130 passenger pigeon fossils have been found scattered across 25 US states, including in the [[La Brea Tar Pits]] of California. These records date as far back as 100,000 years ago in the [[Pleistocene]] era, during which the pigeon's range extended to several western states that were not a part of its modern range. The abundance of the species in these regions and during this time is unknown.<ref name="Blockstein 3"/><ref>{{cite journal |last=Howard |first=H. |author-link=Hildegarde Howard |title=A Pleistocene Record of the Passenger Pigeon in California |journal=Condor |volume=39 |issue=1 |pages=12–14 |year=1937 |jstor=1363481 |doi=10.2307/1363481 |url=http://sora.unm.edu/node/98584}}</ref><ref>{{cite journal |last=Chandler |first=R. M. |title=A Second Pleistocene Passenger Pigeon from California |journal=Condor |volume=84 |issue=2 |page=242 |year=1982 |jstor=1367681 |doi=10.2307/1367681 |url=https://sora.unm.edu/sites/default/files/journals/condor/v084n02/p0242-p0242.pdf}}</ref>

==Ecology and behavior==
[[File:Bird lore (1913) (14562367319).jpg|thumb|left|upright|Live male in Whitman's aviary, 1896/98]]

The passenger pigeon was [[nomad]]ic, constantly migrating in search of food, shelter, or nesting grounds.<ref name="Fuller 2014 30–47"/> In his 1831 ''Ornithological Biography'', American naturalist and artist [[John James Audubon]] described a migration he observed in 1813 as follows:
{{Blockquote|I dismounted, seated myself on an eminence, and began to mark with my pencil, making a dot for every flock that passed. In a short time finding the task which I had undertaken impracticable, as the birds poured in <!--not a mistake-->in countless multitudes, I rose and, counting the dots then put down, found that 163 had been made in twenty-one minutes. I traveled on, and still met more the farther I proceeded. The air was literally filled with Pigeons; the light of noon-day was obscured as by an eclipse; the dung fell in spots, not unlike melting flakes of snow, and the continued buzz of wings had a tendency to lull my senses to repose&nbsp;... I cannot describe to you the extreme beauty of their aerial evolutions, when a hawk chanced to press upon the rear of the flock. At once, like a torrent, and with a noise like thunder, they rushed into a compact mass, pressing upon each other towards the center. In these almost solid masses, they darted forward in undulating and angular lines, descended and swept close over the earth with inconceivable velocity, mounted perpendicularly so as to resemble a vast column, and, when high, were seen wheeling and twisting within their continued lines, which then resembled the coils of a gigantic serpent&nbsp;... Before sunset I reached Louisville, distant from Hardensburgh fifty-five miles. The Pigeons were still passing in undiminished numbers and continued to do so for three days in succession.<ref name=JAA/>}}

These flocks were frequently described as being so dense that they blackened the sky and as having no sign of subdivisions. The flocks ranged from only {{convert|1.0|m|ft|abbr=on}} above the ground in windy conditions to as high as {{convert|400|m|ft|abbr=on}}. These migrating flocks were typically in narrow columns that twisted and undulated, and they were reported as being in nearly every conceivable shape.<ref name="Blockstein 5"/> A skilled flyer, the passenger pigeon is estimated to have averaged {{convert|100|km/h|mph|abbr=on}} during migration. It flew with quick, repeated flaps that increased the bird's velocity the closer the wings got to the body. It was equally adept and quick flying through a forest as through open space. A flock was also adept at following the lead of the pigeon in front of it, and flocks swerved together to avoid a predator. When landing, the pigeon flapped its wings repeatedly before raising them at the moment of landing. The pigeon was awkward when on the ground, and moved around with jerky, alert steps.<ref name="Blockstein 9">{{cite encyclopedia |last=Blockstein |first=D. E. |editor-last=Poole |editor-first=A. |editor2-last=Gill |editor2-first=F. |title=Passenger Pigeon ''Ectopistes migratorius'' |encyclopedia=[[Birds of North America (book)|Birds of North America]] |page=611 |publisher=The Birds of North America, Inc., [[Cornell Lab of Ornithology]] |location=Philadelphia |year=2002 |url=https://birdsoftheworld.org/bow/species/paspig/cur/introduction |url-access=subscription |access-date=October 8, 2024}}</ref>

[[File:Flock of passenger pigeons.jpg|thumb|Illustration of migrating flocks, [[Frank Bond]], 1920]]

The passenger pigeon was one of the most social of all land birds.<ref name="Blockstein 10"/> Estimated to have numbered three to five billion at the height of its population, it may have been the most numerous bird on Earth; researcher [[Arlie W. Schorger]] believed that it accounted for between 25 and 40 percent of the total land bird population in the United States.<ref name="Schorger 205">{{Harvnb|Schorger|1955|p=205}}</ref> The passenger pigeon's historic population is roughly the equivalent of the number of birds that overwinter in the United States every year in the early 21st century.<ref name="Ellsworth"/> Even within their range, the size of individual flocks could vary greatly. In November 1859, [[Henry David Thoreau]], writing in [[Concord, Massachusetts]], noted that "quite a little flock of [passenger] pigeons bred here last summer,"<ref name="Thoreau">{{cite journal |title=General Notes: Thoreau's Notes on the Passenger Pigeon |journal=The Auk |year=1911 |volume=28 |issue=1 |page=111 |jstor=4071503 |doi=10.2307/4071503 |url=https://books.google.com/books?id=wNoUAAAAYAAJ&pg=PA111}}</ref> while only seven years later, in 1866, one flock in southern [[Ontario]] was described as being {{convert|1.5|km|mi|abbr=on}} wide and {{convert|500|km|mi|abbr=on}} long, took 14 hours to pass, and held in excess of 3.5 billion birds.<ref name="sullivan">{{cite book |title=Hunting for Frogs on Elston, and Other Tales from Field & Street |chapter=The Passenger Pigeon: Once There Were Billions |pages=210–213 |date=April 2004 |last1=Sullivan |first1=J. |last2=Sutton |first2=B. |last3=Cronon |first3=W. |publisher=University of Chicago Press |isbn=978-0-226-77993-5 |url=https://press.uchicago.edu/Misc/Chicago/779939pass.html |access-date=February 29, 2012}}</ref> Such a number would likely represent a large fraction of the entire population at the time, or perhaps all of it.<ref name="Extinct Birds"/> Most estimations of numbers were based on single migrating colonies, and it is unknown how many of these existed at a given time. American writer [[Christopher Cokinos]] has suggested that if the birds flew single file, they would have stretched around the Earth 22 times.<ref name="Fuller 2014 50–69"/>

A 2014 genetic study (based on [[coalescent theory]] and on "sequences from most of the [[genome]]" of three individual passenger pigeons) suggested that the passenger pigeon population experienced dramatic fluctuations across the last million years, due to their dependence on availability of [[mast seeding|mast]] (which itself fluctuates). The study suggested the bird was not always abundant, mainly persisting at around 1/10,000 the amount of the several billions estimated in the 1800s, with vastly larger numbers present during outbreak phases.<ref name="Hung 2014">{{cite journal |title=Drastic population fluctuations explain the rapid extinction of the passenger pigeon |journal=[[Proceedings of the National Academy of Sciences]] |volume=111 |issue=29 |pages=10636–10641 |year=2014 |last1=Hung |first1=C. M. |last2=Shaner |first2=P. J. L. |last3=Zink |first3=R. M. |last4=Liu |first4=W. C. |last5=Chu |first5=T. C. |last6=Huang |first6=W. S. |last7=Li |first7=S. H. |display-authors=2 |bibcode=2014PNAS..11110636H |pmid=24979776 |doi=10.1073/pnas.1401526111 |doi-access=free |pmc=4115547}}</ref><ref name="ScienceMag_2014-06-16">{{cite web |title=Humans not solely to blame for passenger pigeon extinction |year=2014 |last1=Williams |first1=S. C. P. |website=Science & AAAS |publisher=[[American Association for the Advancement of Science]] |url=https://www.science.org/content/article/humans-not-solely-blame-passenger-pigeon-extinction |access-date=June 17, 2014}}</ref> Some early accounts also suggest that the appearance of flocks in great numbers was an irregular occurrence.<ref name=Greenway/> These large fluctuations in population may have been the result of a disrupted ecosystem and have consisted of outbreak populations much larger than those common in pre-European times.<ref name="Mann 2011">{{cite book |last=Mann |first=Charles C. |chapter=The Artificial Wilderness |title=[[1491: New Revelations of the Americas Before Columbus]]|edition=2nd |location=New York |publisher=Vintage |year=2011 |pages=365–367|isbn=978-1-4000-4006-3}}</ref> The authors of the 2014 genetic study note that a similar analysis of the human population size arrives at an "[[effective population size]]" of between 9,000 and 17,000 individuals (or approximately 1/550,000th of the peak total human population size of 7 billion cited in the study).<ref name="Hung 2014"/>

For a 2017 genetic study, the authors sequenced the [[genome]]s of two additional passenger pigeons, as well as analyzing the [[mitochondrial DNA]] of 41 individuals.<ref name="Selection"/><ref name="ScienceMag_2017-11-16">{{cite web |title=Four billion passenger pigeons vanished. Their large population may have been what did them in |last1=Pennisi |first1=Elizabeth |author-link=Elizabeth Pennisi |website=Science & AAAS |publisher=[[American Association for the Advancement of Science]] |date=November 16, 2017 |url=https://www.science.org/content/article/four-billion-passenger-pigeons-vanished-their-large-population-may-have-been-what-did |access-date=March 4, 2018}}</ref><ref>{{citation |last=SciShow |title=Why Billions of Passenger Pigeons Died in Under a Century |date=2018-07-02 |url=https://www.youtube.com/watch?v=twr53QVGh0E |access-date=2019-02-15 |url-status=live |archive-url=https://ghostarchive.org/varchive/youtube/20211211/twr53QVGh0E |archive-date=2021-12-11}}{{cbignore}}</ref> This study found evidence that the passenger-pigeon population had been stable for at least the previous 20,000 years.<ref>{{cite news |title=Billions or bust: New genetic clues to the extinction of the passenger pigeon |last=Achenbach |first=Joel |date=November 16, 2017 |newspaper=The Washington Post |url=https://www.washingtonpost.com/news/speaking-of-science/wp/2017/11/16/billions-or-bust-new-genetic-clues-to-the-extinction-of-the-passenger-pigeon/?noredirect=on}}</ref> The study also found that the size of the passenger pigeon population over that time period was larger than the found in the 2014 genetic study. However, the 2017 study's "conservative" estimate of an "[[effective population size]]" of 13 million birds is still only about 1/300th of the bird's estimated historic population of approximately 3–5 billion before their "19th century decline and eventual extinction."<ref name="Selection">{{cite journal |last1=Murray |first1=G. G. R. |last2=Soares |first2=A. E. R. |last3=Novak |first3=B. J. |last4=Schaefer |first4=N. K. |last5=Cahill |first5=J. A. |last6=Baker |first6=A. J. |last7=Demboski |first7=J. R. |last8=Doll |first8=A. |last9=Da Fonseca |first9=R. R. |last10=Fulton |first10=T. L. |last11=Gilbert |first11=M. T. P. |last12=Heintzman |first12=P. D. |last13=Letts |first13=B. |last14=McIntosh |first14=G. |last15=O'Connell |first15=B. L. |display-authors=2 |date=2017 |title=Natural selection shaped the rise and fall of passenger pigeon genomic diversity |journal=Science |volume=358 |issue=6365 |pages=951–954 |bibcode=2017Sci...358..951M |doi=10.1126/science.aao0960 |pmid=29146814 |s2cid=4779202 |doi-access=free |last16=Peck |first16=M. |last17=Pipes |first17=M.-L. |last18=Rice |first18=E. S. |last19=Santos |first19=K. M. |last20=Sohrweide |first20=A. G. |last21=Vohr |first21=S. H. |last22=Corbett-Detig |first22=R. B. |last23=Green |first23=R. E. |last24=Shapiro |first24=B. |hdl=11250/2480523|hdl-access=free }}</ref> A similar study inferring human population size from genetics (published in 2008, and using human mitochondrial DNA and [[Bayesian inference|Bayesian]] [[coalescent theory|coalescent]] inference methods) showed considerable accuracy in reflecting overall patterns of human population growth as compared to data deduced by other means—though the study arrived at a human [[effective population size]] (as of 1600 AD, for Africa, Eurasia, and the Americas combined) that was roughly 1/1000 of the census population estimate for the same time and area based on anthropological and historical evidence.<ref name="Variation">{{cite journal |last1=Atkinson |first1=Q. D. |last2=Gray |first2=R. D. |last3=Drummond |first3=A. J. |title=mtDNA variation predicts population size in humans and reveals a major southern Asian chapter in human prehistory |journal=Molecular Biology and Evolution |date=2008 |volume=25 |issue=2 |pages=468–474 |pmid=18093996 |doi=10.1093/molbev/msm277 |doi-access=free}}</ref><ref name="Essay">{{cite journal |last1=Biraben |first1=J. N. |title=Essai sur l'évolution du nombre des hommes |trans-title=Essay on the evolution of numbers of mankind |journal=Population |series=French Edition |date=1979 |volume=34 |issue=1 |pages=13–25 |jstor=1531855 |doi=10.2307/1531855}}</ref>

The 2017 passenger-pigeon genetic study also found that, in spite of its large population size, the genetic diversity was very low in the species. The authors suggested that this was a side-effect of [[natural selection]], which theory and previous empirical studies suggested could have a particularly great impact on species with very large and cohesive populations.<ref>{{cite journal |last1=Sackton |first1=Timothy B. |last2=Hartl |first2=Daniel L. |last3=Corbett-Detig |first3=Russell B. |title=Natural selection constrains neutral diversity across a wide range of species |date=2015-04-10 |journal=PLOS Biology |language=en |volume=13 |issue=4 |article-number=e1002112 |pmid=25859758 |doi=10.1371/journal.pbio.1002112 |doi-access=free |pmc=4393120}}</ref><ref>{{cite journal |last1=Przeworski |first1=Molly |last2=Andolfatto |first2=Peter |last3=Venkat |first3=Aarti |last4=Ségurel |first4=Laure |last5=Meyer |first5=Wynn K. |last6=Matute |first6=Daniel R. |last7=Bullaughey |first7=Kevin |last8=Leffler |first8=Ellen M. |title=Revisiting an old riddle: what determines genetic diversity levels within species? |date=2012-09-11 |journal=PLOS Biology |language=en |volume=10 |issue=9 |article-number=e1001388 |pmid=22984349 |doi=10.1371/journal.pbio.1001388 |doi-access=free |pmc=3439417}}</ref> Natural selection can reduce genetic diversity over extended regions of a genome through '[[selective sweep]]s' or '[[background selection]]'. The authors found evidence of a faster rate of [[adaptation|adaptive evolution]] and faster removal of harmful mutations in passenger pigeons compared to [[band-tailed pigeon]]s, which are some of passenger pigeons' closest living relatives. They also found evidence of lower genetic diversity in regions of the passenger pigeon genome that have lower rates of [[genetic recombination]]. This is expected if natural selection, via [[selective sweep]]s or [[background selection]], reduced their genetic diversity, but not if population instability did. The study concluded that earlier suggestion that population instability contributed to the extinction of the species was invalid.<ref name="Selection"/> Evolutionary biologist A. Townsend Peterson said of the two passenger-pigeon genetic studies (published in 2014 and 2017) that, though the idea of extreme fluctuations in the passenger-pigeon population was "deeply entrenched," he was persuaded by the 2017 study's argument, due to its "in-depth analysis" and "massive data resources."<ref name="ScienceMag_2017-11-16"/>

[[File:Ectopistes migratoriusAAP042CA.jpg|thumb|left|Juvenile (left), male (center), female (right), [[Louis Agassiz Fuertes]], 1910]]

A [[communally roosting]] species, the passenger pigeon chose roosting sites that could provide shelter and enough food to sustain their large numbers for an indefinite period. The time spent at one roosting site may have depended on the extent of human persecution, weather conditions, or other, unknown factors. Roosts ranged in size and extent, from a few acres to {{convert|260|km2|sqmi|abbr=on}} or greater. Some roosting areas would be reused for subsequent years, others would only be used once.<ref name="Fuller 2014 30–47"/> The passenger pigeon roosted in such numbers that even thick tree branches would break under the strain. The birds frequently piled on top of each other's backs to roost. They rested in a slumped position that hid their feet. They slept with their bills concealed by the feathers in the middle of the breast while holding their tail at a 45-degree angle.<ref name="Blockstein 9"/> Dung could accumulate under a roosting site to a depth of over {{convert|0.3|m|ft|1|abbr=on}}.<ref name="Blockstein 8"/>

[[File:Bird-lore (1913) (14568824740).jpg|thumb|upright|Alert parent bird posing defiantly towards the camera (1896, published 1913)]]

If the pigeon became alert, it would often stretch out its head and neck in line with its body and tail, then nod its head in a circular pattern. When aggravated by another pigeon, it raised its wings threateningly, but passenger pigeons almost never actually fought. The pigeon bathed in shallow water, and afterwards lay on each side in turn and raised the opposite wing to dry it.<ref name="Blockstein 9"/>

The passenger pigeon drank at least once a day, typically at dawn, by fully inserting its bill into lakes, small ponds, and streams. Pigeons were seen perching on top of each other to access water, and if necessary, the species could alight on open water to drink.<ref name="Blockstein 8">{{Harvnb|Blockstein|2002|p=8}}</ref> One of the primary causes of natural mortality was the weather, and every spring many individuals froze to death after migrating north too early. In captivity, a passenger pigeon was capable of living at least 15 years; [[Martha (pigeon)|Martha]], the last known living passenger pigeon, was at least 17 and possibly as old as 29 when she died. It is undocumented how long wild pigeons lived.<ref name="Blockstein 15"/>

The bird is believed to have played a significant ecological role in the composition of [[pre-Columbian era|pre-Columbian]] forests of eastern North America. For instance, while the passenger pigeon was extant, forests were dominated by [[Quercus alba|white oaks]]. This species germinated in the fall, therefore making its seeds almost useless as a food source during the spring breeding season, while [[Quercus rubra|red oaks]] produced acorns during the spring, which the pigeons devoured. The absence of the passenger pigeon's seed consumption may have contributed to the modern dominance of red oaks. Due to the immense amount of dung present at roosting sites, few plants grew for years after the pigeons left. Also, the accumulation of flammable debris (such as limbs broken from trees and foliage killed by excrement) at these sites may have increased both the frequency and intensity of [[wildfire|forest fires]], which would have favored [[fire ecology#Fire tolerance|fire-tolerant species]], such as [[Quercus macrocarpa|bur oaks]], [[Quercus velutina|black oaks]], and [[Quercus alba|white oaks]] over less fire-tolerant species, such as red oaks, thus helping to explain the change in the composition of eastern forests since the passenger pigeon's extinction (from white oaks, bur oaks, and black oaks predominating in presettlement forests, to the "dramatic expansion" of red oaks today).<ref name="Ellsworth">{{cite journal |last=Ellsworth |first=J. W. |author2=McComb, B. C. |title=Potential Effects of Passenger Pigeon Flocks on the Structure and Composition of Presettlement Forests of Eastern North America |journal=[[Conservation Biology (journal) |Conservation Biology]] |volume=17 |issue=6 |pages=1548–1558 |year=2003 |bibcode=2003ConBi..17.1548E |doi=10.1111/j.1523-1739.2003.00230.x |s2cid=55427679}}</ref>

A study released in 2018 concluded that the "vast numbers" of passenger pigeons present for "tens of thousands of years" would have influenced the evolution of the tree species whose seeds they ate. Those masting trees that produced seeds during the spring nesting season (such as red oaks) evolved so that some portion of their seeds would be too large for passenger pigeons to swallow (thus allowing some of their seeds to escape predation and grow new trees). White oak, in contrast, with its seeds sized consistently in the edible range, evolved an irregular masting pattern that took place in the fall, when fewer passenger pigeons would have been present. The study further concluded that this allowed white oaks to be the dominant tree species in regions where passenger pigeons were commonly present in the spring.<ref name="evolve">{{cite journal |last1=Novak |first1=B. J. |last2=Estes |first2=J. A. |last3=Shaw |first3=H. E. |last4=Novak |first4=E. V. |last5=Shapiro |first5=B. |title=Experimental investigation of the dietary ecology of the extinct passenger pigeon, ''Ectopistes migratorius'' |journal=Frontiers in Ecology and Evolution |date=2018 |volume=6 |article-number=20 |doi=10.3389/fevo.2018.00020 |doi-access=free|bibcode=2018FrEEv...6...20N }}</ref>

With the large numbers in passenger pigeon flocks, the excrement they produced was enough to destroy surface-level vegetation at long-term roosting sites, while adding high quantities of nutrients to the [[ecosystem]]. Because of this—along with the breaking of tree limbs under their collective weight and the great amount of [[mast seeding|mast]] they consumed—passenger pigeons are thought to have influenced both the structure of eastern forests and the composition of the species present there.<ref name="Ellsworth"/> Due to these influences, some ecologists have considered the passenger pigeon a [[keystone species]],<ref name="Hung 2014"/> with the disappearance of their vast flocks leaving a major gap in the ecosystem.<ref name="McCauley 2016">{{cite journal |title=A mammoth undertaking: harnessing insight from functional ecology to shape de-extinction priority setting |journal=[[Functional Ecology (journal) |Functional Ecology]] |volume=31 |issue=5 |pages=1008–1009 |year=2016 |last1=McCauley |first1=D. J. |last2=Hardesty-Moore |first2=M. |last3=Halpern |first3=B. S. |last4=Young |first4=H. S. |last5=Seddon |first5=P. |display-authors=2 |doi=10.1111/1365-2435.12728 |s2cid=19791653 |url=https://escholarship.org/content/qt5cd8p3cr/qt5cd8p3cr.pdf?t=ozrwe2}}</ref> Their role in creating [[forest dynamics|forest disturbances]] has been linked to greater vertebrate diversity in forests by creating more niches for animals to fill.<ref>{{cite journal |last1=Hutchinson |first1=Todd F. |last2=Yaussy |first2=Daniel A. |last3=Long |first3=Robert P. |last4=Rebbeck |first4=Joanne |last5=Sutherland |first5=Elaine Kennedy |title=Long-term (13-year) effects of repeated prescribed fires on stand structure and tree regeneration in mixed-oak forests |date=December 2012 |journal=Forest Ecology and Management |volume=286 |pages=87–100 |bibcode=2012ForEM.286...87H |issn=0378-1127 |doi=10.1016/j.foreco.2012.08.036}}</ref> To help fill that ecological gap, it has been proposed that modern land managers attempt to replicate some of their effects on the ecosystem by creating openings in forest [[canopy (biology)|canopies]] to provide more [[understory]] light.<ref name="Buchanan 2012">{{cite journal |last=Buchanan |first=M. L. |author2=Hart, J. L. |title=Canopy disturbance history of old-growth ''Quercus alba'' sites in the eastern United States: Examination of long-term trends and broad-scale patterns |journal=[[Forest Ecology and Management]] |volume=267 |issue=267 |pages=28–39 |year=2012 |bibcode=2012ForEM.267...28B |doi=10.1016/j.foreco.2011.11.034}}</ref>

The [[American chestnut]] trees that provided much of the [[mast seeding|mast]] on which the passenger pigeon fed was itself almost driven to extinction by an imported Asian fungus ([[chestnut blight]]) around 1905. As many as thirty billion trees are thought to have died as a result in the following decades, but this did not affect the passenger pigeon, which was already extinct in the wild at the time.<ref name="Fuller 2014 30–47"/>

After the disappearance of the passenger pigeon, the population of another acorn feeding species, the [[white-footed mouse]], grew exponentially because of the increased availability of the seeds of the oak, beech, and chestnut trees.<ref>{{cite journal |jstor=1312946 |title=Of Mice and Mast |journal=BioScience |volume=46 |issue=5 |page=323 |year=1996 |last1=Ostfeld |first1=Richard S. |last2=Jones |first2=Clive G. |last3=Wolff |first3=Jerry O. |doi=10.2307/1312946 |doi-access=free |s2cid=89496723}}</ref> It has been speculated<ref>{{cite journal |title=Lyme Disease and the Passenger Pigeon? |journal=Science |volume=279 |issue=5358 |pages=1831c–1831 |year=1998 |last1=Blockstein |first1=D. E. |bibcode=1998Sci...279.1831B |pmid=9537894 |doi=10.1126/science.279.5358.1831c |s2cid=45065236}}</ref> that the extinction of passenger pigeons may have increased the prevalence of tick-borne [[lyme disease]] in modern times as white-footed mice are the [[natural reservoir|reservoir hosts]] of ''[[Borrelia burgdorferi]]''.<ref>{{cite book |title=The Annihilation of Nature: Human Extinction of Birds and Mammals |last2=Ehrlich |first2=A. H. |last3=Ehrlich |first3=P. R. |publisher=Johns Hopkins University Press |year=2015 |isbn=978-1-4214-1718-9 |location=Baltimore, Maryland |pages=33–35 |via=Open Edition |last1=Ceballos |first1=G.}}</ref>

===Diet===
[[File:Passenger pigeons (Ectopistes migratorius) in autumn 1.jpg|left|thumb|Taxidermied specimens mounted as if foraging for [[Quercus palustris|pin oak]] acorns, at the [[American Museum of Natural History]].]]
[[Beech]]es and [[oak]]s produced the [[mast seeding|mast]] needed to support nesting and roosting flocks.<ref name="Blockstein 7"/> The passenger pigeon changed its diet depending on the season. In the fall, winter, and spring, it mainly ate beechnuts, [[acorn]]s, and chestnuts. During the summer, berries and softer fruits, such as [[blueberry|blueberries]], [[grape]]s, [[Prunus|cherries]], [[Morus rubra|mulberries]], [[Phytolacca americana|pokeberries]], and [[Cornus canadensis|bunchberry]], became the main objects of its consumption. It also ate [[Oligochaeta|worms]], [[caterpillar]]s, [[snail]]s, and other invertebrates, particularly while breeding.<ref name="Fuller 2014 30–47"/><ref name="Blockstein 6">{{Harvnb|Blockstein|2002|p=6}}</ref> It took advantage of cultivated grains, particularly [[buckwheat]], when it found them. It was especially fond of [[salt]], which it ingested either from brackish springs or salty soil.<ref name="Blockstein 7">{{Harvnb|Blockstein|2002|p=7}}</ref>

Mast occurs in large quantities in different places at different times, and rarely in consecutive years, which is one of the reasons why the large flocks were constantly on the move. As mast is produced during autumn, there would have to be a large amount of it left by the summer, when the young were reared. It is unknown how they located this fluctuating food source, but their eyesight and flight powers helped them survey large areas for places that could provide food enough for a temporary stay.<ref name="Extinct Birds"/><ref name="Fuller 2014 30–47"/>

[[File:Passenger Pigeon organs.jpg|thumb|upright|Internal organs of Martha, the last individual: cr. denotes the crop, gz. the [[gizzard]], 1915]]

The passenger pigeon foraged in flocks of tens or hundreds of thousands of individuals that overturned leaves, dirt, and snow with their bills in search of food. One observer described the motion of such a flock in search of mast as having a rolling appearance, as birds in the back of the flock flew overhead to the front of the flock, dropping leaves and grass in flight.<ref name="Fuller 2014 30–47"/><ref name="Blockstein 6"/> The flocks had wide leading edges to better scan the landscape for food sources.<ref name="Blockstein 7"/>

When nuts on a tree loosened from their caps, a pigeon would land on a branch and, while flapping vigorously to stay balanced, grab the nut, pull it loose from its cap, and swallow it whole. Collectively, a foraging flock was capable of removing nearly all fruits and nuts from their path. Birds in the back of the flock flew to the front in order to pick over unsearched ground; however, birds never ventured far from the flock and hurried back if they became isolated. It is believed that the pigeons used social cues to identify abundant sources of food, and a flock of pigeons that saw others feeding on the ground often joined them.<ref name="Blockstein 6"/> During the day, the birds left the roosting forest to forage on more open land.<ref name="Blockstein 5"/> They regularly flew {{convert|100|to|130|km|mi|abbr=on}} away from their roost daily in search of food, and some pigeons reportedly traveled as far as {{convert|160|km|mi|abbr=on}}, leaving the roosting area early and returning at night.<ref name="Fuller 2014 30–47"/><ref name="Ellsworth"/>

The passenger pigeon's very elastic mouth and throat and a joint in the lower bill enabled it to swallow acorns whole. It could store large quantities of food in its [[crop (anatomy)#Birds|crop]], which could expand to about the size of an orange, causing the neck to bulge and allowing a bird quickly to grab any food it discovered. The crop was described as being capable of holding at least 17 acorns or 28 beechnuts, 11 grains of corn, 100 maple seeds, plus other material; it was estimated that a passenger pigeon needed to eat about {{convert|61|cm3|in3|abbr=on}} of food a day to survive. If shot, a pigeon with a crop full of nuts would fall to the ground with a sound described as like the rattle of a bag of marbles. After feeding, the pigeons perched on branches and digested the food stored in their crop overnight<ref name="Fuller 2014 30–47"/><ref name="Blockstein 6"/><ref name="Ellsworth"/> with the aid of a muscular [[gizzard]], which often [[gastrolith|contained gravel]].<ref>{{cite journal|url=https://birdsoftheworld.org/bow/species/paspig/cur/foodhabits|title=Passenger Pigeon (''Ectopistes migratorius''): Diet and Foraging|website=All About Birds|publisher=Cornell Lab of Ornithology|last=Blockstein|first=D.E.|year=2020|editor-last1=Poole|editor-first1=A.F.|editor-last2=Gill|editor-first2=F.B.|location=Ithaca, New York, USA|version=1.0|doi=10.2173/bow.paspig.01|access-date=11 October 2024|url-access=subscription}}</ref>

The pigeon could eat and digest {{convert|100|g|oz|abbr=on}} of acorns per day.<ref>{{cite journal |title=Human-wildlife competition and the passenger pigeon: Population growth from system destabilization |journal=[[Human Ecology (journal) |Human Ecology]] |volume=13 |issue=4 |pages=389–410 |year=1985 |last1=Neumann |first1=T. W. |bibcode=1985HumEc..13..389N |doi=10.1007/BF01531152 |s2cid=153426755}}</ref> At the historic population of three billion passenger pigeons, this amounted to {{convert|210,000,000|L|gal|abbr=on}} of food a day.<ref name="Ellsworth"/> The pigeon could regurgitate food from its crop when more desirable food became available.<ref name="Fuller 2001">{{cite book |last=Fuller |first=E. |title=Extinct Birds |edition=Revised |publisher=Comstock Publishing Associates |year=2001 |location=Ithaca, New York |isbn=978-0-8014-3954-4 |pages=96–97}}</ref> A 2018 study found that the dietary range of the passenger pigeon was restricted to certain sizes of seed, due to the size of its gape. This would have prevented it from eating some of the seeds of trees such as [[Quercus rubra|red oaks]], [[Quercus velutina|black oaks]], and the [[American chestnut]]. Specifically, the study found that between 13% and 69% of red oak seeds were too large for passenger pigeons to have swallowed, that only a "small proportion" of the seeds of black oaks and American chestnuts were too large for the birds to consume, and that all white oak seeds were sized within an edible range. They also found that seeds would be completely destroyed during digestion, which therefore hindered dispersal of seeds this way. Instead, passenger pigeons may have spread seeds by [[regurgitation (digestion)|regurgitation]], or after dying.<ref name="evolve"/>

===Reproduction===
[[File:Birdonnest.jpg|thumb|upright|Nesting captive bird, wary of the photographer]]

Other than finding roosting sites, the migrations of the passenger pigeon were connected with finding places appropriate for this [[communally breeding]] bird to nest and raise its young. It is not certain how many times a year the birds bred; once seems most likely, but some accounts suggest more. The nesting period lasted around four to six weeks. The flock arrived at a nesting ground around March in southern latitudes, and some time later in more northern areas.<ref name="Fuller 2014 30–47"/><ref name="Schorger 205"/> The pigeon had no site fidelity, often choosing to nest in a different location each year.<ref name="Blockstein 15"/> The formation of a nesting colony did not necessarily take place until several months after the pigeons arrived on their breeding grounds, typically during late March, April, or May.<ref name="Blockstein 11"/>

The colonies, which were known as "cities", were immense, ranging from {{convert|49|ha|acre|abbr=on}} to thousands of hectares in size, and were often long and narrow in shape (L-shaped), with a few areas untouched for unknown reasons. Due to the topography, they were rarely continuous. Since no accurate data was recorded, it is not possible to give more than estimates on the size and population of these nesting areas, but most accounts mention colonies containing millions of birds. The largest nesting area ever recorded was in central Wisconsin in 1871; it was reported as covering {{convert|2,200|km2|sqmi|abbr=on}}, with the number of birds nesting there estimated to be around 136,000,000. As well as these "cities", there were regular reports of much smaller flocks or even individual pairs setting up a nesting site.<ref name="Fuller 2014 30–47"/><ref name="Blockstein 11">{{Harvnb|Blockstein|2002|p=11}}</ref> The birds do not seem to have formed as vast breeding colonies at the periphery of their range.<ref name=Greenway/>

Courtship took place at the nesting colony.<ref name="Blockstein 10">{{Harvnb|Blockstein|2002|p=10}}</ref> Unlike other pigeons, courtship took place on a branch or perch. The male, with a flourish of the wings, made a "keck" call while near a female. The male then gripped tightly to the branch and vigorously flapped his wings up and down. When the male was close to the female, he then pressed against her on the perch with his head held high and pointing at her.<ref name="Blockstein 9"/> If receptive, the female pressed back against the male.<ref name="Blockstein 10"/> When ready to mate, the pair [[social grooming|preened]] each other. This was followed by the birds [[beak#Billing|billing]], in which the female inserted its [[beak|bill]] into and clasped the male's bill, shook for a second, and separated quickly while standing next to each other. The male then scrambled onto the female's back and copulated, which was then followed by soft clucking and occasionally more preening.<ref name="Blockstein 10"/> John James Audubon described the courtship of the passenger pigeon as follows:

[[File:Nestandegg.jpg|thumb|left|Nest and egg in Whitman's aviary]]
{{Blockquote|Thither the countless myriads resort, and prepare to fulfill one of the great laws of nature. At this period the note of the Pigeon is a soft coo-coo-coo-coo much shorter than that of the domestic species. The common notes resemble the monosyllables kee-kee-kee-kee, the first being the loudest, the others gradually diminishing In power. The male assumes a pompous demeanor, and follows the female, whether on the ground or on the branches, with spread tail and drooping wings, which it rubs against the part over which it is moving. The body is elevated, the throat swells, the eyes sparkle. He continues his notes, and now and then rises on the wing, and flies a few yards to approach the fugitive and timorous female. Like the domestic Pigeon and other species, they caress each other by billing, in which action, the bill of the one is introduced transversely into that of the other, and both parties alternately disgorge the contents of their crop by repeated efforts.<ref name=JAA/>}}

After observing captive birds, Wallace Craig found that this species did less charging and strutting than other pigeons (as it was awkward on the ground), and thought it probable that no food was transferred during their brief billing (unlike in other pigeons), and he therefore considered Audubon's description partially based on analogy with other pigeons as well as imagination.<ref name="Craig 1911"/><ref name="Blockstein 9"/>

[[File:Pigeon migrateur MHNT.jpg|thumb|Preserved egg, [[Muséum de Toulouse]]]]

Nests were built immediately after pair formation and took two to four days to construct; this process was highly synchronized within a colony.<ref name="Blockstein 11"/> The female chose the nesting site by sitting on it and flicking her wings. The male then carefully selected nesting materials, typically twigs, and handed them to the female over her back. The male then went in search of more nesting material while the female constructed the nest beneath herself. Nests were built between {{convert|2.0|and|20.1|m|ft|abbr=on}} above the ground, though typically above {{convert|4.0|m|ft|abbr=on}}, and were made of 70 to 110 twigs woven together to create a loose, shallow bowl through which the egg could easily be seen. This bowl was then typically lined with finer twigs. The nests were about {{convert|150|mm|in|abbr=on}} wide, {{convert|61|mm|in|abbr=on}} high, and {{convert|19|mm|in|abbr=on}} deep. Though the nest has been described as crude and flimsy compared to those of many other birds, remains of nests could be found at sites where nesting had taken place several years prior. Nearly every tree capable of supporting nests had them, often more than 50 per tree; one hemlock was recorded as holding 317 nests. The nests were placed on strong branches close to the tree trunks. Some accounts state that ground under the nesting area looked as if it had been swept clean, due to all the twigs being collected at the same time, yet this area would also have been covered in dung.<ref name="Fuller 2014 30–47"/><ref name="Fuller 2001"/><ref name="Blockstein 12">{{Harvnb|Blockstein|2002|p=12}}</ref> As both sexes took care of the nest, the pairs were [[monogamy in animals|monogamous]] for the duration of the nesting.<ref name="Blockstein 9"/>

[[File:Young passenger pigeon.jpg|thumb|left|Live nestling or squab]]

Generally, the eggs were laid during the first two weeks of April across the pigeon's range.<ref name="Blockstein 11"/> Each female laid its egg immediately or almost immediately after the nest was completed; sometimes the pigeon was forced to lay it on the ground if the nest was not complete.<ref name="Blockstein 13">{{Harvnb|Blockstein|2002|p=13}}</ref> The normal clutch size appears to have been a single egg, but there is some uncertainty about this, as two have also been reported from the same nests.<ref name="Fuller 2014 30–47"/> Occasionally, a second female laid its egg in another female's nest, resulting in two eggs being present.<ref name="Blockstein 14"/> The egg was white and oval shaped and averaged {{convert|40|by|34|mm|in|abbr=on}} in size.<ref name="Blockstein 12"/> If the egg was lost, it was possible for the pigeon to lay a replacement egg within a week.<ref name="Blockstein 13"/> A whole colony was known to re-nest after a snowstorm forced them to abandon their original colony.<ref name="Blockstein 15">{{Harvnb|Blockstein|2002|p=15}}</ref> Both parents [[egg incubation|incubated]] The egg for 12 to 14 days, with the male incubating it from midmorning to midafternoon and the female incubating it the rest of the time.<ref name="Fuller 2014 30–47"/><ref name="Blockstein 13"/>

Upon hatching, the nestling (or squab) was blind and sparsely covered with yellow, hairlike [[down feather|down]].<ref name="Blockstein 13"/> The nestling developed quickly and within 14 days weighed as much as its parents. During this brooding period both parents took care of the nestling, with the male attending in the middle of the day and the female at other times. The nestlings were fed [[crop milk]] (a substance similar to [[curd]], produced in the crops of the parent birds) exclusively for the first days after hatching. Adult food was gradually introduced after three to six days. After 13 to 15 days, the parents fed the nestling for a last time and then abandoned it, leaving the nesting area ''en masse''. The nestling begged in the nest for a day or two, before climbing from the nest and fluttering to the ground, whereafter it moved around, avoided obstacles, and begged for food from nearby adults. It was another three or four days before it fledged.<ref name="Fuller 2014 30–47"/><ref name="Blockstein 14">{{Harvnb|Blockstein|2002|p=14}}</ref> The entire nesting cycle lasted about 30 days.<ref name="Fuller 2001"/> It is unknown whether colonies re-nested after a successful nesting.<ref name="Blockstein 15"/> The passenger pigeon sexually matured during its first year and bred the following spring.<ref name="Blockstein 14"/>

[[Alfred Russel Wallace]], in his historic 1858 paper [[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection]], used the passenger pigeon as an example of an immensely successful species despite laying fewer eggs than most other birds:

{{Blockquote|It would therefore appear that, as far as the continuance of the species and the keeping up the average number of individuals are concerned, large broods are superfluous. On the average all above one become food for hawks and kites, wild cats, and weasels, or perish of cold and hunger as winter comes on. This is strikingly proved by the case of particular species; for we find that their abundance in individuals bears no relation whatever to their fertility in producing offspring. Perhaps the most remarkable instance of an immense bird population is that of the passenger pigeon of the United States, which lays only one, or at most two eggs, and is said to rear generally but one young one. Why is this bird so extraordinarily abundant, while others producing two or three times as many young are much less plentiful? The explanation is not difficult. The food most congenial to this species, and on which it thrives best, is abundantly distributed over a very extensive region, offering such differences of soil and climate, that in one part or another of the area the supply never fails. The bird is capable of a very rapid and long-continued flight, so that it can pass without fatigue over the whole of the district it inhabits, and as soon as the supply of food begins to fail in one place is able to discover a fresh feeding-ground. This example strikingly shows us that the procuring a constant supply of wholesome food is almost the sole condition requisite for ensuring the rapid increase of a given species, since neither the limited fecundity, nor the unrestrained attacks of birds of prey and of man are here sufficient to check it. In no other birds are these peculiar circumstances so strikingly combined. Either their food is more liable to failure, or they have not sufficient power of wing to search for it over an extensive area, or during some season of the year it becomes very scarce, and less wholesome substitutes have to be found; and thus, though more fertile in offspring, they can never increase beyond the supply of food in the least favourable seasons.<ref>{{citation |last=Darwin |given1=Charles |author-link1=Charles Darwin |surname2=Wallace |given2=Alfred Russel |author-link2=Alfred Russel Wallace |year=1858 |title=On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection |journal=Zoological Journal of the Linnean Society |volume=3 |issue=9  |pages=46–62 |doi=10.1111/j.1096-3642.1858.tb02500.x |doi-access=free |url=https://darwin-online.org.uk/content/frameset?itemID=F350&viewtype=text&pageseq=1 |access-date=14 January 2007}}</ref>}}

===Predators and parasites===
[[File:Passenger pigeon.jpg|thumb|upright|Immature bird; the young were vulnerable to predators after leaving the nest]]

Nesting colonies attracted large numbers of predators, including [[American mink]]s (''Neogale vison''), [[long-tailed weasel]]s (''Neogale frenata''), [[American marten]]s (''Martes americana''), and [[raccoon]]s (''Procyon lotor'') that preyed on eggs and nestlings, [[birds of prey]], such as [[owl]]s, [[hawk]]s, and [[eagle]]s that preyed on nestlings and adults, and [[gray wolf|wolves]] (''Canis lupus''), [[fox]]es (''Urocyon cinereoargenteus'' and ''Vulpes vulpes''), [[bobcat]]s (''Lynx rufus''), [[American black bear]]s (''Ursus americanus''), and [[cougar]]s (''Puma concolor'') that preyed on injured adults and fallen nestlings. Hawks of the genus ''[[Accipiter]]'' and falcons pursued and preyed upon pigeons in flight, which in turn executed complex aerial maneuvers to avoid them; [[Cooper's hawk]] (''Accipiter cooperii'') was known as the "great pigeon hawk" due to its successes, and these hawks allegedly followed migrating passenger pigeons.<ref name="Blockstein 10"/> While many predators were drawn to the flocks, individual pigeons were largely protected due to the sheer size of the flock, and overall little damage could be inflicted on the flock by predation.<ref name="Blockstein 10"/> Despite the number of predators, nesting colonies were so large that they were estimated to have a 90% success rate if not disturbed.<ref name="Blockstein 15"/> After being abandoned and leaving the nest, the very fat juveniles were vulnerable to predators until they were able to fly. The sheer number of juveniles on the ground meant that only a small percentage of them were killed; [[predator satiation]] may therefore be one of the reasons for the extremely social habits and communal breeding of the species.<ref name="Fuller 2014 30–47"/><ref name="Fuller 2014 72–88"/>

Two parasites have been recorded on passenger pigeons. One species of [[Philopteridae|phtilopterid]] [[louse]], ''[[Columbicola extinctus]]'', was originally thought to have lived on just passenger pigeons and to have become [[coextinct]] with them. This was proven inaccurate in 1999 when ''C.&nbsp;extinctus'' was rediscovered living on band-tailed pigeons.<ref name="Clayton1999">{{cite journal |last=Clayton |first=D. H. |author2=Price, R. D. |title=Taxonomy of New World Columbicola (Phthiraptera: Philopteridae) from the Columbiformes (Aves), with descriptions of five new species |journal=Annals of the Entomological Society of America |volume=92 |issue=5 |pages=675{{ndash}}685 |year=1999 |doi=10.1093/aesa/92.5.675 |url=https://darwin.biology.utah.edu/PDFs/42.pdf |access-date=October 8, 2024 |url-status=live |archive-date=April 25, 2012 |archive-url=https://web.archive.org/web/20120425124314/http://darwin.biology.utah.edu/PubsHTML/PDF-Files/42.pdf}}</ref><ref name="Price2000"/> This, and the fact that the related louse ''C.&nbsp;angustus'' is mainly found on cuckoo-doves, further supports the relation between these pigeons, as the phylogeny of lice broadly mirrors that of their hosts.<ref name=Johnson/> Another louse, ''[[Campanulotes|Campanulotes defectus]]'', was thought to have been unique to the passenger pigeon, but is now believed to have been a case of a contaminated specimen, as the species is considered to be the still-extant ''[[Campanulotes|Campanulotes flavus]]'' of Australia.<ref name="Price2000">{{cite journal |last=Price |first=R. D. |author2=Clayton, D. H. |author3=Adams, R. J. |title=Pigeon Lice Down Under: Taxonomy of Australian ''Campanulotes'' (Phthiraptera: Philopteridae), with a description of ''C. durdeni'' n.sp. |journal=[[Journal of Parasitology]] |volume=86 |issue=5 |pages=948–950 |year=2000 |jstor=3284803 |pmid=11128516 |doi=10.2307/3284803 |url=https://darwin.biology.utah.edu/PDFs/47.pdf |access-date=October 8, 2024 |url-status=live |archive-url=https://web.archive.org/web/20100610153220/http://darwin.biology.utah.edu/PubsHTML/PDF-Files/47.pdf |archive-date=June 10, 2010}}</ref> There is no record of a wild pigeon dying of either disease or parasites.<ref name="Blockstein 15"/>

==Relationship with humans==
[[File:Mershon's The Passenger Pigeon (Audubon plate, crop).jpg|thumb|left|upright|Billing pair by [[John James Audubon]], from ''[[The Birds of America]]'', 1827–1838. This image has been criticized for its scientific inaccuracy.]]
For fifteen thousand years or more before the arrival of Europeans in the Americas, passenger pigeons and Native Americans coexisted in the forests of what would later become the eastern part of the continental United States.<ref name="archaeology">{{Harvnb |Greenberg|2014 |pp=[https://books.google.com/books?id=6SLBAgAAQBAJ&pg=PA31 31–35]}}</ref><ref name="pre-clovis">{{citation |last=Goodyear |first=Albert C. |title=Evidence of Pre-Clovis Sites in the Eastern United States |journal=Paleoamerican Origins: Beyond Clovis |year=2005 |pages=103–112 |url=https://scholarcommons.sc.edu/cgi/viewcontent.cgi?article=1026&context=sciaa_staffpub}}</ref><ref name="Figure 1B">{{citation |last=Novak |first=Ben J. |title=Deciphering The Ecological Impact of the Passenger Pigeon: A Synthesis of Paleogenetics, Paleoecology, Morphology, and Physiology |work=UC Santa Cruz |year=2016 |pages=10–11 |url=https://escholarship.org/content/qt3260s35t/qt3260s35t.pdf}}</ref> A study published in 2008 found that, throughout most of the [[Holocene]], Native American land-use practices greatly influenced forest composition. The regular use of [[controlled burn]]s, the [[girdling]] of unwanted trees, and the planting and tending of favored trees suppressed the populations of a number of tree species that did not produce nuts, acorns, or fruit, while increasing the populations of numerous tree species that did. In addition, the burning away of forest-floor litter made these foods easier to find, once they had fallen from the trees.<ref name="influenced">{{citation |last1=Abrams |first1=Marc D. |last2=Nowacki |first2=Gregory J. |title=Native Americans as active and passive promoters of mast and fruit trees in the eastern USA |journal=The Holocene |volume=18 |issue=7 |year=2008 |pages=1123–1137 |bibcode=2008Holoc..18.1123A |doi=10.1177/0959683608095581 |s2cid=128836416}}</ref> Some have argued that such Native American land-use practices increased the populations of various animal species, including the passenger pigeon, by increasing the food available to them,<ref name="explains">{{citation |last1=Delcourt |first1=Paul A. |last2=Delcourt |first2=Hazel R. |title=Prehistoric Native Americans and Ecological Change: Human Ecosystems in Eastern North America Since the Pleistocene |publisher=Cambridge University Press |place=Cambridge |series=Cambridge Studies in Ecology |edition=1st |year=2004 |isbn=978-0-521-66270-3 |url=https://books.google.com/books?id=BUIki2XK7BgC&pg=PA4}}</ref><ref name="favored">{{cite book |last=Little |first=Silas |chapter=7. Effects on Forests: Northeastern United States – I. Frequency and Type of Presettlement Fires |editor1-last=Kozlowski |editor1-first=T. T. |editor2-last=Ahlgren |editor2-first=C. E. |title=Fire and Ecosystems |date=1974 |chapter-url=https://books.google.com/books?id=Nrg-EP-1oVcC&pg=PA226 |location=New York |publisher=Academic Press |page=226 |isbn=978-0-12-424255-5}}</ref><ref name="abundance">{{citation |last1=Thompson |first1=D. Q. |last2=Smith |first2=R. H. |name-list-style=amp |title=The forest primeval in the northeast -- a great myth? |work=Proceedings Annual [10th] Tall Timbers Fire Ecology Conference: a quest for ecological understanding. Fredericton, New Brunswick, Canada |location=Tallahassee, FL |publisher=Tall Timbers Research |pages=261–265 |year=1971 |url=https://talltimbers.org/wp-content/uploads/2014/03/ThompsonandSmith1970_op.pdf}}</ref> while elsewhere it has been claimed that, by hunting passenger pigeons and competing with them for some kinds of nuts and acorns, Native Americans suppressed their population size.<ref name="claim">{{Harvnb |Greenberg|2014|p=[https://books.google.com/books?id=3-qnBQAAQBAJ&pg=PA34 34]}}</ref> Genetic research may shed some light on this question. A 2017 study of passenger-pigeon DNA found that the passenger-pigeon population size was stable for 20,000 years prior to its 19th-century decline and subsequent extinction, while a 2016 study of ancient Native American DNA found that the Native American population went through a period of rapid expansion, increasing 60-fold, starting about 13–16 thousand years ago. If both of these studies are correct, then a great change in the size of the Native American population had no apparent impact on the size of the passenger-pigeon population. This suggests that the net effect of Native American activities on passenger-pigeon population size was neutral.<ref name="Selection"/><ref name="expansion">{{citation |last1=Llamas |first1=B. |last2=Fehren-Schmitz |first2=L. |last3=Valverde |first3=G. |last4=Soubrier |first4=J. |last5=Mallick |first5=S. |last6=Rohland |first6=N. |last7=Nordenfelt |first7=S. |last8=Valdiosera |first8=C. |last9=Richards |first9=S. M. |last10=Rohrlach |first10=A. |last11=Romero |first11=M. I. B. |last12=Espinoza |first12=I. F. |last13=Cagigao |first13=E. T. |last14=Jiménez |first14=L. W. |last15=Makowski |first15=K. |last16=Reyna |first16=I. S. L. |last17=Lory |first17=J. M. |last18=Torrez |first18=J. A. B. |last19=Rivera |first19=M. A. |last20=Burger |first20=R. L. |last21=Ceruti |first21=M. C. |last22=Reinhard |first22=J. |last23=Wells |first23=R. S. |last24=Politis |first24=G. |last25=Santoro |first25=C. M. |last26=Standen |first26=V. G. |last27=Smith |first27=C |last28=Reich |first28=D |last29=Ho |first29=S. Y. W. |last30=Cooper |first30=A |last31=Haak |first31=W. |display-authors=2 |title=Ancient mitochondrial DNA provides high-resolution time scale of the peopling of the Americas |journal=Science Advances |volume=2 |issue=4 |pages=1–10 |year=2016 |bibcode=2016SciA....2E1385L |pmid=27051878 |doi=10.1126/sciadv.1501385 |pmc=4820370}}</ref>

The passenger pigeon played a religious role for some northern Native American tribes. The [[Wyandot people]] (or Huron) believed that every twelve years during the [[Feast of the Dead]], the souls of the dead changed into passenger pigeons, which were then hunted and eaten.<ref name="Schorger135">{{Harvnb|Schorger|1955|p=135}}</ref> Before hunting the juvenile pigeons, the Seneca people made an offering of [[wampum]] and brooches to the old passenger pigeons; these were placed in a small kettle or other receptacle by a smoky fire.<ref name="Schorger135"/> The [[Ho-Chunk]] people considered the passenger pigeon to be the bird of the chief, as they were served whenever the chieftain gave a feast.<ref name="Schorger136">{{Harvnb|Schorger|1955|p=136}}</ref> The Seneca people believed that a white pigeon was the chief of the passenger pigeon colony, and that a Council of Birds decided that the pigeons had to give their bodies to the Seneca because they were the only birds that nested in colonies. The Seneca developed a pigeon dance as a way of showing their gratitude.<ref name="Schorger136"/>

French explorer [[Jacques Cartier]] was the first European to report on passenger pigeons, during his voyage in 1534.<ref>{{cite magazine |last1=Edey |first1=M. |title=Once there were billions, now there are none |magazine=[[Life (magazine) |Life]] |date=December 22, 1961 |volume=51 |issue=25 |pages=169{{ndash}}176 |issn=0024-3019 |url=https://books.google.com/books?id=blMEAAAAMBAJ&pg=PA170 |access-date=June 16, 2015}}</ref> The bird was subsequently observed and noted by historical figures such as [[Samuel de Champlain]] and [[Cotton Mather]]. Most early accounts dwell on the vast number of pigeons, the resulting darkened skies, and the enormous amount of hunted birds (50,000 birds were reportedly sold at a Boston market in 1771).<ref name="Fuller 2014 50–69">{{Harvnb|Fuller|2014|pp=50–69}}</ref> The early colonists thought that large flights of pigeons would be followed by ill fortune or sickness. When the pigeons wintered outside of their normal range, some believed that they would have "a sickly summer and autumn."<ref name="Schorger12">{{Harvnb|Schorger|1955|p=12}}</ref> In the 18th and 19th centuries, various parts of the pigeon were thought to have medicinal properties. The blood was supposed to be good for eye disorders, the powdered stomach lining was used to treat [[dysentery]], and the dung was used to treat a variety of ailments, including headaches, stomach pains, and lethargy.<ref name="Schorger1323">{{Harvnb|Schorger|1955|pp=132–133}}</ref> Though they did not last as long as the feathers of a goose, the feathers of the passenger pigeon were frequently used for bedding. Pigeon feather beds were so popular that for a time in [[Saint-Jérôme, Quebec]], every dowry included a bed and pillows made of pigeon feathers. In 1822, one family in [[Chautauqua County, New York]], killed 4,000 pigeons in a day solely for this purpose.<ref name="Schorger132">{{Harvnb|Schorger|1955|p=132}}</ref>

[[File:Ectopistes migratoriusMCN2P28CA.jpg|thumb|upright|Painting of a male, K.&nbsp;Hayashi, c.&nbsp;1900]]

The passenger pigeon was featured in the writings of many significant early naturalists, as well as accompanying illustrations. Mark Catesby's 1731 illustration, the first published depiction of this bird, is somewhat crude, according to some later commentators. The original watercolor that the engraving is based on was bought by the British royal family in 1768, along with the rest of Catesby's watercolors. The naturalists [[Alexander Wilson (ornithologist)|Alexander Wilson]] and John James Audubon both witnessed large pigeon migrations first hand, and published detailed accounts wherein both attempted to deduce the total number of birds involved. The most famous and often reproduced depiction of the passenger pigeon is Audubon's illustration (handcolored [[aquatint]]) in his book ''[[The Birds of America]]'', published between 1827 and 1838. Audubon's image has been praised for its artistic qualities, but criticized for its supposed scientific inaccuracies. As Wallace Craig and R.&nbsp;W. Shufeldt (among others) pointed out, the birds are shown perched and billing one above the other, whereas they would instead have done this side by side, the male would be the one passing food to the female, and the male's tail would not be spread. Craig and Shufeldt instead cited illustrations by American artist [[Louis Agassiz Fuertes]] and Japanese artist K.&nbsp;Hayashi as more accurate depictions of the bird. Illustrations of the passenger pigeon were often drawn after stuffed birds, and [[Charles R. Knight]] is the only "serious" artist known to have drawn the species from life. He did so on at least two occasions; in 1903 he drew a bird possibly in one of the three aviaries with surviving birds, and some time before 1914, he drew Martha, the last individual, in the [[Cincinnati Zoo]].<ref name=JAA>{{cite book |author-link=John James Audubon |last=Audubon |first=J. J. |title=Ornithological biography, or, an account of the Habits of the Birds of the United States of America |volume=1 |publisher=A. Black |location=Edinburgh |year=1835 |pages=319–327 |url=https://www.biodiversitylibrary.org/item/103784#page/347/mode/1up}}</ref><ref name="Fuller 2014 50–69"/><ref name="Fuller 2014 124–147">{{Harvnb|Fuller|2014|pp=124–147}}</ref><ref>{{cite journal |last=Shufeldt |first=R. W. |title=Published figures and plates of the extinct passenger pigeon |journal=[[Scientific Monthly]] |volume=12 |issue=5 |edition=5th |pages=458{{ndash}}481 |url=https://archive.org/stream/publishedfigures00shuf#page/458/mode/2up |year=1921 |bibcode=1921SciMo..12..458S}}</ref><ref>{{cite book |last1=Milner |first1=R. |year=2012 |page=138 |title=Charles R. Knight: The Artist Who Saw Through Time |publisher=[[Abrams Books]] |isbn=978-0-8109-8479-0 |location=New York}}</ref><ref name="Craig 1911"/>

The bird has been written about (including in poems, songs,{{efn-ua|[[John Herald]], a [[bluegrass music|bluegrass]] singer, wrote a song dedicated to the extinction of the species and [[Martha (pigeon)|Martha]], the species' endling, that he titled "Martha (Last of the Passenger Pigeons)".<ref>{{cite web |title=Lyrics to "Martha (Last of the Passenger Pigeons)" |website=Johnherald.com |author-link=John Herald |last1=Herald |first1=J. |url=http://johnherald.com/martha.shtml |access-date=April 28, 2013}}</ref><ref>{{cite web |title=Martha: Last of the Passenger Pigeons |last1=Gebhart |first1=Parrish |format=video |website=[[YouTube]] |date=October 17, 2010 |url=https://www.youtube.com/watch?v=XFpaVfFIMFQ |access-date=December 12, 2013 |url-status=live |archive-url=https://ghostarchive.org/varchive/youtube/20211211/XFpaVfFIMFQ |archive-date=2021-12-11}}{{cbignore}}</ref> In connection with the centennial of Martha's death, the song was cited as evidence of her [[secular icon|iconic]] stature{{mdash}}a symbol of the wanton slaughter of these pigeons and the human-caused extinction of the species.<ref name="Harvey">{{cite journal |title=13 Memories of Martha, the Last Passenger Pigeon |last1=Harvey |first1=C. |last2=Newbern |first2=E. |date=August 29, 2014 |journal=[[Audubon Magazine]] |url=https://www.audubon.org/news/13-memories-martha-last-passenger-pigeon |access-date=March 3, 2016}}</ref><ref name="McLendon">{{cite journal |title=Ode to Martha, the last passenger pigeon |last1=McLendon |first1=R. |journal=[[Mother Nature Network]] |date=September 1, 2011 |url=https://www.treehugger.com/ode-to-martha-the-last-passenger-pigeon-4866790 |access-date=March 3, 2016 |quote=One of eastern North America's most iconic animals vanished forever on Sept. 1, 1914. Now, 97 years later, the passenger pigeon has become an icon for something else: manmade extinction.}}</ref>}} and fiction) and illustrated by many notable writers and artists, and is depicted in art to this day, for example in [[Walton Ford]]'s 2002 painting ''Falling Bough'', and [[National Medal of Arts]] winner [[John A. Ruthven]]'s 2014 mural in Cincinnati, which commemorates the 100th anniversary of Martha's death.<ref name="Fuller 2014 124–147"/> The "Project Passenger Pigeon" outreach group used the centennial of its extinction to spread awareness about human-induced extinction, and to recognize its relevance in the 21st century. It has been suggested that the passenger pigeon could be used as a "[[flagship]]" species to spread awareness of other threatened, but less well-known North American birds.<ref>{{cite journal |last1=Kyne |first1=P. M. |last2=Adams |first2=V. M. |title=Extinct flagships: linking extinct and threatened species |journal=Oryx |date=2016 |volume=51 |issue=3 |pages=471–476 |doi=10.1017/S0030605316000041 |doi-access=free}}</ref>

===Hunting===
[[File:Passenger pigeon shoot.jpg|left|thumb|Depiction of a shooting in northern Louisiana, Smith Bennett, 1875]]

The passenger pigeon was an important source of food for the people of North America.<ref name="Schorger129">{{Harvnb|Schorger|1955|p=129}}</ref> Native Americans ate pigeons, and tribes near nesting colonies would sometimes move to live closer to them and eat the juveniles, killing them at night with long poles.<ref name="Schorger1334">{{Harvnb|Schorger|1955|pp=133–134}}</ref> Many Native Americans were careful not to disturb the adult pigeons, and instead ate only the juveniles as they were afraid that the adults might desert their nesting grounds; in some tribes, disturbing the adult pigeons was considered a crime.<ref name="Schorger137">{{Harvnb|Schorger|1955|p=137}}</ref> Away from the nests, large nets were used to capture adult pigeons, sometimes up to 800 at a time.<ref name="Schorger139">{{Harvnb|Schorger|1955|p=139}}</ref> Low-flying pigeons could be killed by throwing sticks or stones. At one site in [[Oklahoma]], the pigeons leaving their roost every morning flew low enough that the [[Cherokee]] could throw clubs into their midst, which caused the lead pigeons to try to turn aside and in the process created a blockade that resulted in a large mass of flying, easily hit pigeons.<ref name="Schorger168"/> Among the game birds, passenger pigeons were second only to the [[wild turkey]] (''Meleagris gallopavo'') in terms of importance for the Native Americans living in the southeastern United States. The bird's fat was stored, often in large quantities, and used as butter. Archaeological evidence supports the idea that Native Americans ate the pigeons frequently prior to colonization.<ref name="Schorger134">{{Harvnb|Schorger|1955|p=134}}</ref>

[[File:Passenger pigeon capture.jpg|thumb|upright|1881 spread showing methods of trapping pigeons for shooting contests]]

What may be the earliest account of Europeans hunting passenger pigeons dates to January 1565, when the French explorer [[René Goulaine de Laudonnière|René Laudonnière]] wrote of killing close to 10,000 of them around [[Fort Caroline#Fort Caroline (1564–1565)|Fort Caroline]] in a matter of weeks:
{{Blockquote|There came to us a manna of wood pigeons in such great numbers, that over a span of about seven weeks, each day we killed more than two hundred with [[arquebus]]es in the woods around our fort.<ref name=Manna >{{cite book |last=Laudonnière |first=René de Goulaine de |title=L'histoire notable de la Floride située ès Indes Occidentales: contenant les trois voyages faits en icelle par certains Capitaines et Pilotes françois |date=1853 |location=Paris |publisher=Chez P. Jannet |page=136 |url=https://books.google.com/books?id=lohbAAAAQAAJ&pg=PA136}}</ref><ref>{{cite magazine |last1=MacNamara |first1=Charles |editor1-last=Miller |editor1-first=G.A. |title=Champlain as a Naturalist |magazine=The Canadian Field-Naturalist |volume=XL |issue=6 |location=Ottawa |publisher=Graphic Publishers |page=127 |url=https://archive.org/details/canadianfieldnat1926otta}}</ref>}}

This amounted to about one passenger pigeon per day for each person in the fort.<ref name=each >{{cite book |last=McCarthy |first=Kevin M. |title=Twenty Florida Pirates |date=1994 |location=Sarasota, FL |publisher=Pineapple Press |page=[https://archive.org/details/twentyfloridapir0000mcca/page/16 16] |isbn=978-1-56164-050-8 |url=https://archive.org/details/twentyfloridapir0000mcca |url-access=registration |quote=its leader, Rene de Laudonniere, had been there 200 soldiers without relief over a year, since June 1564..}}</ref>

After European colonization, the passenger pigeon was hunted with more intensive methods than the more [[sustainability|sustainable]] methods practiced by the natives.<ref name="Fuller 2014 72–88"/> The passenger pigeon was of particular value on the frontier, and some settlements counted on its meat to support their population.<ref name="Schorger130">{{Harvnb|Schorger|1955|p=130}}</ref><ref name="Schorger131">{{Harvnb|Schorger|1955|p=131}}</ref> The flavor of the flesh of passenger pigeons varied depending on how they were prepared. In general, juveniles were thought to taste the best, followed by birds fattened in captivity and birds caught in September and October. It was common practice to fatten trapped pigeons before eating them or storing their bodies for winter.<ref name="Schorger129"/> Dead pigeons were commonly stored by [[salting (food)|salting]] or [[pickling]] the bodies; other times, only the breasts of the pigeons were kept, in which case they were typically [[smoking (cooking)|smoked]]. In the early 19th century, commercial hunters began netting and shooting the birds to sell as food in city markets, and even as pig [[fodder]]. Once pigeon meat became popular, commercial hunting started on a prodigious scale.<ref name="Schorger131"/><ref name="Schorger144"/>

Passenger pigeons were shot with such ease that many did not consider them to be a game bird, as an amateur hunter could easily bring down six with one shotgun blast; a particularly good shot with both barrels of a shotgun at a roost could kill 61 birds.<ref name="Schorger186">{{Harvnb|Schorger|1955|p=186}}</ref><ref name="Schorger193">{{Harvnb|Schorger|1955|p=193}}</ref> The birds were frequently shot either in flight during migration or immediately after, when they commonly perched in dead, exposed trees.<ref name="Schorger186"/> Hunters only had to shoot toward the sky without aiming, and many pigeons would be brought down.<ref name="Fuller 2014 72–88">{{Harvnb|Fuller|2014|pp=72–88}}</ref> The pigeons proved difficult to shoot head-on, so hunters typically waited for the flocks to pass overhead before shooting them. Trenches were sometimes dug and filled with grain so that a hunter could shoot the pigeons along this trench.<ref name="Schorger192">{{Harvnb|Schorger|1955|p=192}}</ref> Hunters largely outnumbered trappers, and hunting passenger pigeons was a popular sport for young boys.<ref name="Schorger198">{{Harvnb|Schorger|1955|p=198}}</ref> In 1871, a single seller of ammunition provided three tons of powder and 16 tons (32,000&nbsp;lb) of shot during a nesting. In the latter half of the 19th century, thousands of passenger pigeons were captured for use in the [[sports shooting]] industry. The pigeons were used as living targets in shooting tournaments, such as "[[trap-shooting]]", the controlled release of birds from special traps. Competitions could also consist of people standing regularly spaced while trying to shoot down as many birds as possible in a passing flock.<ref name="Fuller 2014 72–88"/><ref name="Hume 2015">{{cite journal |last=Hume |first=J. P. |title=Large-scale live capture of Passenger Pigeons ''Ectopistes migratorius'' for sporting purposes: overlooked illustrated documentation |journal=Bulletin of the British Ornithologists' Club |volume=135 |series=2 |pages=174{{ndash}}184 |year=2015 |url=https://boc-online.org/passenger-pigeons-large-scale-live-capture}}</ref> The pigeon was considered so numerous that 30,000 birds had to be killed to claim the prize in one competition.<ref name="Fuller 2001"/>

[[File:Passenger Pigeon Net Cockburn 1829.jpg|thumb|left|Pigeon net in Canada, by [[James Pattison Cockburn]], 1829]]

Humans used a wide variety of other methods to capture and kill passenger pigeons. Nets were propped up to allow passenger pigeons entry, and then closed by knocking loose the stick that supported the opening, trapping twenty or more pigeons inside.<ref name="Schorger169">{{Harvnb|Schorger|1955|p=169}}</ref> Tunnel nets were also used to great effect, and one particularly large net was capable of catching 3,500 pigeons at a time.<ref name="Schorger172">{{Harvnb|Schorger|1955|p=172}}</ref> These nets were used by many farmers on their own property as well as by professional trappers.<ref name="Schorger170">{{Harvnb|Schorger|1955|p=170}}</ref> Food would be placed on the ground near the nets to attract the pigeons. [[Decoy]] or "stool pigeons" (sometimes blinded by having their eyelids sewn together) were tied to a stool. When a flock of pigeons passed by, a cord would be pulled that made the stool pigeon flutter to the ground, making it seem as if it had found food, and the flock would be lured into the trap.<ref name="Fuller 2014 72–88"/><ref name="Schorger1779">{{Harvnb|Schorger|1955|pp=177–179}}</ref><ref>{{cite journal |author=Paxson, H. D. |title=The last of the Wild Pigeon in Bucks County |pages=367{{ndash}}382 |journal=Collection of Papers Read Before the Bucks County Historical Society |volume=4 |year=1917 |url=https://archive.org/stream/collectionofpape04buck#page/n389/mode/1up}}</ref> Salt was also frequently used as bait, and many trappers set up near salt springs.<ref name="Schorger173">{{Harvnb|Schorger|1955|p=173}}</ref> At least one trapper used alcohol-soaked grain as bait to intoxicate the birds and make them easier to kill.<ref name="Schorger168">{{Harvnb|Schorger|1955|p=168}}</ref> Another method of capture was to hunt at a nesting colony, particularly during the period of a few days after the adult pigeons abandoned their nestlings, but before the nestlings could fly. Some hunters used sticks to poke the nestlings out of the nest, while others shot the bottom of a nest with a blunt arrow to dislodge the pigeon. Others cut down a nesting tree in such a way that when it fell, it would also hit a second nesting tree and dislodge the pigeons within.<ref name="Schorger141">{{Harvnb|Schorger|1955|p=141}}</ref> In one case, {{convert|6|km2|acre|abbr=on}} of large trees were speedily cut down to get birds, and such methods were common.<ref name="Fuller 2014 72–88"/> A severe method was to set fire to the base of a tree nested with pigeons; the adults would flee and the juveniles would fall to the ground.<ref name="Yeoman"/><ref name="Schorger142">{{Harvnb|Schorger|1955|p=142}}</ref> [[Sulfur]] was sometimes burned beneath the nesting tree to suffocate the birds, which fell out of the tree in a weakened state.<ref name="Schorger167">{{Harvnb|Schorger|1955|p=167}}</ref>

[[File:Decoy Passenger Pigeon.jpg|thumb|upright|Trapper Albert Cooper with blind [[decoy]] pigeons for luring wild birds, c.&nbsp;1870]]

By the mid-19th century, [[railroad]]s had opened new opportunities for pigeon hunters. While it was once extremely difficult to ship masses of pigeons to eastern cities, railway access permitted pigeon hunting to become commercialized.<ref name="Schorger144">{{Harvnb|Schorger|1955|p=144}}</ref> An extensive [[telegraph]] system was introduced in the 1860s, which improved communication across the United States, making it easier to spread information about the whereabouts of pigeon flocks.<ref name="Hume 2015"/> After being opened up to the railroads, the town of [[Plattsburgh (city), New York|Plattsburgh, New York]], is estimated to have shipped 1.8 million pigeons to larger cities in 1851 alone at a price of 31 to 56 cents a dozen. By the late 19th century, the trade of passenger pigeons had become commercialized. Large commission houses employed trappers (known as "pigeoners") to follow the flocks of pigeons year-round.<ref name="Schorger145">{{Harvnb|Schorger|1955|p=145}}</ref> A single hunter is reported to have sent three million birds to eastern cities during his career.<ref name="Ehrlich">{{cite web |title=The Passenger Pigeon |year=1988 |last1=Ehrlich |first1=P. R. |author-link1=Paul R. Ehrlich |last2=Dobkin |first2=D. S. |last3=Wheye |first3=D. |website=[[Stanford University]] |url=https://web.stanford.edu/group/stanfordbirds/text/essays/Passenger_Pigeon.html |access-date=March 3, 2012}}</ref> In 1874, at least 600 people were employed as pigeon trappers, a number which grew to 1,200 by 1881. Pigeons were caught in such numbers that by 1876, shipments of dead pigeons were unable to recoup the costs of the barrels and ice needed to ship them.<ref name="Schorger146">{{Harvnb|Schorger|1955|p=146}}</ref> The price of a barrel full of pigeons dropped to below fifty cents, due to overstocked markets. Passenger pigeons were instead kept alive so their meat would be fresh when killed, and sold once their market value had increased. Thousands of birds were kept in large pens, though the bad conditions led many to die from lack of food and water, and by fretting (gnawing) themselves; many rotted away before they could be sold.<ref name="Fuller 2014 50–69"/>

Hunting of passenger pigeons was documented and depicted in contemporaneous newspapers, wherein various trapping methods and uses were featured. The most often reproduced of these illustrations was captioned "Winter sports in northern Louisiana: shooting wild pigeons", and published in 1875. Passenger pigeons were also seen as [[agricultural pests]], because feeding flocks could destroy entire crops. The bird was described as a "perfect scourge" by some farming communities, and hunters were employed to "wage warfare" on the birds to save grain, as shown in another newspaper illustration from 1867 captioned as "Shooting wild pigeons in Iowa".<ref name="Hume 2015"/> When comparing these "pests" to the [[bison]] of the Great Plains, the valuable resource needed was not the species of animals but the agriculture which was consumed by said animal. The crops that were eaten were seen as marketable calories, proteins, and nutrients all grown for the wrong species.<ref>{{cite journal |last1=Whaples |first1=R. |year=2015 |title=A Feathered River Across the Sky: The Passenger Pigeon's Flight to Extinction |journal=[[The Independent Review]] |volume=19 |issue=3 |pages=443{{ndash}}6}}</ref><ref name=ext>{{cite journal |last1=Jackson |first1=J. A. |last2=Jackson |first2=B. |year=2007 |title=Extinction: the Passenger Pigeon, last hopes, letting go |journal=[[The Wilson Journal of Ornithology]] |volume=119 |issue=4 |pages=767{{ndash}}772|jstor=20456089 |doi=10.1676/1559-4491(2007)119[767:etpplh]2.0.co;2 |s2cid=85830808}}</ref>

===Decline and conservation attempts===
[[File:Mershon's The Passenger Pigeon (frontispiece, crop).jpg|thumb|left|upright|Male and female by [[Louis Agassiz Fuertes]], [[book frontispiece|frontispiece]] of [[William Butts Mershon]]'s 1907 ''The Passenger Pigeon'']]

The notion that the species could be driven to [[extinction]] was alien to the early colonists, because the number of birds did not appear to diminish, and also because the concept of extinction was yet to be defined. The bird seems to have been slowly pushed westward after the arrival of Europeans, becoming scarce or absent in the east, though there were still millions of birds in the 1850s. The population must have been decreasing in numbers for many years, though this went unnoticed due to the apparent vast number of birds, which clouded their decline.<ref name="Fuller 2014 50–69"/> In 1856 Bénédict Henry Révoil may have been one of the first writers to voice concern about the fate of the passenger pigeon, after witnessing a hunt in 1847:
{{Blockquote|Everything leads to the belief that the pigeons, which cannot endure isolation and are forced to flee or to change their way of living according to the rate at which North America is populated by the European inflow, will simply end by disappearing from this continent, and, if the world does not end this before a century, I will wager&nbsp;... that the amateur of ornithology will find no more wild pigeons, except those in the Museums of Natural History.<ref name="Fuller 2014 50–69"/>}}

[[File:Alabama bird day book (1915) (14751712302).jpg|thumb|upright|Life drawing by [[Charles R. Knight]], 1903]]
By the 1870s, the decrease in birds was noticeable, especially after the last large-scale nestings and subsequent slaughters of millions of birds in 1874 and 1878. By this time, large nestings only took place in the north, around the Great Lakes. The last large nesting was in [[Petoskey, Michigan]], in 1878 (following one in Pennsylvania a few days earlier), where 50,000 birds were killed each day for nearly five months. The surviving adults attempted a second nesting at new sites, but were killed by professional hunters before they had a chance to raise any young. Scattered nestings were reported into the 1880s, but the birds were now wary, and commonly abandoned their nests if persecuted.<ref name="Extinct Birds"/><ref name=SI/><ref name="Fuller 2014 50–69"/>

By the time of these last nestings, laws had already been enacted to protect the passenger pigeon, but these proved ineffective, as they were unclearly framed and hard to enforce. H.&nbsp;B. Roney, who witnessed the Petoskey slaughter, led campaigns to protect the pigeon, but was met with resistance, and accusations that he was exaggerating the severity of the situation. Few offenders were prosecuted, mainly some poor trappers, but the large enterprises were not affected.<ref name="Fuller 2014 50–69"/> In 1857, a bill was brought forth to the [[Ohio State Legislature]] seeking protection for the passenger pigeon, yet a Select Committee of the Senate filed a report stating that the bird did not need protection, being "wonderfully prolific", and dismissing the suggestion that the species could be destroyed.<ref>{{cite book |last1=Hornaday |first1=W. T. |author-link=William Temple Hornaday |place=New York |publisher=[[Charles Scribner's Sons]] |year=1913 |title=Our Vanishing Wild Life. Its Extermination and Preservation |url=https://www.gutenberg.org/files/13249/13249-h/13249-h.htm |access-date=February 29, 2012}} at [[Project Gutenberg]].</ref> Public protests against trap-shooting erupted in the 1870s, as the birds were badly treated before and after such contests. Conservationists were ineffective in stopping the slaughter. A bill was passed in the Michigan legislature making it illegal to net pigeons within {{convert|3|km|mi|abbr=on}} of a nesting area. In 1897, a bill was introduced in the Michigan legislature asking for a 10-year closed season on passenger pigeons. Similar legal measures were passed and then disregarded in Pennsylvania. The gestures proved futile and, by the mid-1890s, the passenger pigeon had almost completely disappeared, and was probably extinct as a breeding bird in the wild.<ref name="Hume 2015"/><ref name="Ehrlich"/> Small flocks are known to have existed at this point, since large numbers of birds were still being sold at markets. Thereafter, only small groups or individual birds were reported, many of which were shot on sight.<ref name="Fuller 2014 50–69"/>

===Last survivors===
{{See also|Martha (passenger pigeon)}}
[[File:Last known Passenger Pigeon.jpg|thumb|"Buttons", one of the last confirmed wild passenger pigeons, [[Cincinnati Zoo]]]]

The last recorded nest and egg in the wild were collected in 1895 near Minneapolis. The last wild individual in Louisiana was discovered among a flock of mourning doves in 1896, and subsequently shot. Many late sightings are thought to be false or due to confusion with mourning doves.<ref name="Fuller 2014 50–69"/> The last fully authenticated record of a wild passenger pigeon was near [[Oakford, Illinois]], on March 12, 1901, when a male bird was killed, stuffed, and placed in [[Millikin University]] in [[Decatur, Illinois]], where it remains today. This was not discovered until 2014, when writer Joel Greenberg found out the date of the bird's shooting while doing research for his book ''A Feathered River Across the Sky.'' Greenberg also pointed out a record of a male shot near [[Laurel, Indiana]], on April 3, 1902, that was stuffed but later destroyed.<ref>{{cite book |last1=Greenberg |first1=Joel |title=A Feathered River Across the Sky: The Passenger Pigeon's Flight to Extinction |publisher=[[Bloomsbury Publishing |Bloomsbury USA]] |year=2014 |location=New York |isbn=978-1-62040-534-5}}</ref>

For many years, the last confirmed wild passenger pigeon was thought to have been shot near [[Sargents, Ohio|Sargents]], [[Pike County, Ohio]] on March 24, 1900, when a boy named Press Clay Southworth killed a female bird with a [[BB gun]].<ref name=SI/><ref name="Reeve">{{cite journal |last=Reeve |first=S. |title=Going Down in History |journal=Geographical |volume=73 |issue=3 |pages=60{{ndash}}64 |date=March 2001 |issn=0016-741X}}</ref> The boy did not recognize the bird as a passenger pigeon, but his parents identified it, and sent it to a taxidermist. The specimen, nicknamed "Buttons" due to the buttons used instead of glass eyes, was donated to the [[Ohio Historical Society]] by the family in 1915. The reliability of accounts after the Ohio, Illinois, and Indiana birds are in question. Ornithologist [[Alexander Wetmore]] claimed that he saw a pair flying near [[Independence, Kansas]], in April 1905.<ref>{{cite news |last1=Wetmore |first1=A. |title=Game Birds of Prairie, Forest and Tundra |date=October 1936 |page=495 |work=[[National Geographic (magazine) |National Geographic]]}}</ref><ref>{{cite journal |last1=McKinley |first1=D. |year=1960 |title=A History of the Passenger Pigeon in Missouri |journal=Auk |volume=77 |issue=4 |pages=399–420 |jstor=4082414 |doi=10.2307/4082414 |doi-access=free |url=https://sora.unm.edu/node/20911}}</ref> On May 18, 1907, U.S. President [[Theodore Roosevelt]] claimed to have seen a "flock of about a dozen two or three times on the wing" while on retreat at his cabin in Pine Knot, Virginia, and that they lit on a dead tree "in such a characteristically pigeon-like attitude"; this sighting was corroborated by a local gentleman whom he had "rambled around with in the woods a good deal" and whom he found to be "a singularly close observer."<ref>{{cite web |title=Theodore Roosevelt Signed Archive Passenger Pigeons {{!}} Raab Collection |website=The Raab Collection |language=en-US |url=https://www.raabcollection.com/presidential-autographs/roosevelt-pigeons |access-date=2023-03-12}}</ref><ref>{{cite web |title=Letter from Theodore Roosevelt to C. Hart Merriam |website=theodorerooseveltcenter.org |url=https://www.theodorerooseveltcenter.org/Research/Digital-Library/Record/ImageViewer?libID=o199420 |access-date=2023-03-12}}</ref> In 1910, the [[American Ornithologists' Union]] offered a reward of $3,000 for discovering a nest— {{Inflation|US|3000|1910|fmt=eq|cursign=$}}.{{inflation/fn|US}}<ref>{{cite web |title=Passenger Pigeon |website=South Dakota Game Fish & Parks |last1=Stukel |first1=E. D. |date=January–February 2005 |url=http://gfp.sd.gov/wildlife/critters/birds/passenger-pigeon.aspx |access-date=August 7, 2016}}</ref><ref>{{cite news |work=[[The New York Times]] |title=Reward for Wild Pigeons. Ornithologists Offer $3,000 for the Discovery of Their Nests |date=April 4, 1910 |place=Boston, Massachusetts |url=https://timesmachine.nytimes.com/timesmachine/1910/04/04/104928421.pdf |access-date=February 29, 2012}}</ref>

[[File:Passenger pigeon aviary.jpg|thumb|left|Whitman's aviary with passenger pigeons and other species, 1896/98]]

Most captive passenger pigeons were kept for exploitative purposes, but some were housed in zoos and aviaries. Audubon alone claimed to have brought 350 birds to England in 1830, distributing them among various noblemen, and the species is also known to have been kept at [[London Zoo]]. Being common birds, these attracted little interest, until the species became rare in the 1890s. By the turn of the 20th century, the last known captive passenger pigeons were divided in three groups; one in Milwaukee, one in Chicago, and one in Cincinnati. There are claims of a few further individuals having been kept in various places, but these accounts are not considered reliable today. The Milwaukee group was kept by David Whittaker, who began his collection in 1888, and possessed fifteen birds some years later, all descended from a single pair.<ref name="Extinct Birds"/><ref name="Fuller 2014 92–121"/>

The Chicago group was kept by [[Charles Otis Whitman]], whose collection began with passenger pigeons bought from Whittaker beginning in 1896. He had an interest in studying pigeons, and kept his passenger pigeons with other pigeon species. Whitman brought his pigeons with him from Chicago to Massachusetts by railcar each summer. By 1897, Whitman had bought all of Whittaker's birds, and upon reaching a maximum of 19 individuals, he gave seven back to Whittaker in 1898. Around this time, a series of photographs were taken of these birds; 24 of the photos survive. Some of these images have been reproduced in various media, copies of which are now kept at the [[Wisconsin Historical Society]]. It is unclear exactly where, when, and by whom these photos were taken, but some appear to have been taken in Chicago in 1896, others in Massachusetts in 1898, the latter by a J.&nbsp;G. Hubbard. By 1902, Whitman owned sixteen birds. His pigeons laid many eggs, but few hatched, and many hatchlings died. A newspaper inquiry was published that requested "fresh blood" to the flock which had now ceased breeding. By 1907, he was down to two female passenger pigeons that died that winter, and was left with two infertile male hybrids, whose subsequent fate is unknown. By this time, only four (all males) of the birds Whitman returned to Whittaker were alive, and these died between November 1908 and February 1909.<ref name="Fuller 2014 92–121">{{Harvnb|Fuller|2014|pp=92–121}}</ref><ref name="Rothschild">{{cite book |last=Rothschild |first=W. |author-link=Walter Rothschild, 2nd Baron Rothschild |title=Extinct Birds |publisher=[[Hutchinson (publisher)|Hutchinson & Co]] |year=1907 |location=London |pages=167{{ndash}}170 |url=https://archive.org/stream/extinctbirdsatte00roth#page/166/mode/2up}}</ref>

[[File:Hornaday Frontispiece.jpg|right|upright=1.5|thumb|"''The Folly of 1857 and the Lesson of 1912''", frontispiece to [[William Temple Hornaday|William T. Hornaday]]'s ''Our vanishing wild life'' (1913), showing [[Martha (passenger pigeon)|Martha]] in life, the [[endling]] of the species.]]
The Cincinnati Zoo, one of the oldest zoos in the United States, kept passenger pigeons from its beginning in 1875. The zoo kept more than twenty individuals in a {{convert|10|by|12|ft|m|adj=on|spell=in}} cage.<ref name="Fuller 2014 92–121"/> Passenger pigeons do not appear to have been kept at the zoo due to their rarity, but to enable guests to have a closer look at a native species.<ref name=Schorger28>{{Harvnb|Schorger|1955|p=28}}</ref> Recognizing the decline of the wild populations, Whitman and the Cincinnati Zoo consistently strove to breed the surviving birds, including attempts at making a rock dove foster passenger pigeon eggs.<ref>{{cite journal |last=D'Elia |first=J. |title=Evolution of Avian Conservation Breeding with Insights for Addressing the Current Extinction Crisis |journal=Journal of Fish and Wildlife Management |volume=1 |issue=2 |pages=189–210 |year=2010 |doi=10.3996/062010-JFWM-017 |doi-access=free|bibcode=2010JWFM....1..189D }}</ref> In 1902, Whitman gave a female passenger pigeon to the zoo; this was possibly the individual later known as Martha, which would become the last living member of the species. Other sources argue that Martha was hatched at the Cincinnati Zoo, lived there for 25 years, and was the descendant of three pairs of passenger pigeons purchased by the zoo in 1877. It is thought this individual was named Martha because her last cage mate was named George, thereby honoring [[George Washington]] and his wife [[Martha Washington|Martha]], though it has also been claimed she was named after the mother of a zookeeper's friends.<ref name="Fuller 2014 92–121"/><ref name=Schorger27>{{Harvnb|Schorger|1955|p=27}}</ref>

In 1909, Martha and her two male companions at the Cincinnati Zoo became the only known surviving passenger pigeons. One of these males died around April that year, followed by George, the remaining male, on July 10, 1910.<ref name=Schorger28/> It is unknown whether the remains of George were preserved. Martha soon became a celebrity due to her status as an [[endling]], and offers of a $1,000 reward ({{inflation|US|1000|1909|fmt=eq}}){{inflation/fn|US}} for finding a mate for her brought even more visitors to see her. During her last four years in solitude (her cage was {{convert|5.4|by|6|m|ft|abbr=on}}), Martha became steadily slower and more immobile; visitors would throw sand at her to make her move, and her cage was roped off in response.<ref name="Fuller 2014 92–121"/><ref name=Shell>{{cite journal |last=Shell |first=H. R. |title=The Face of Extinction |journal=[[Natural History (magazine) |Natural History]] |volume=113 |issue=4 |page=72 |date=May 2004 |issn=0028-0712}}</ref> Martha died of old age on September 1, 1914, and was found lifeless on the floor of her cage.<ref name=Shufeldt/><ref name=Schorger29>{{Harvnb|Schorger|1955|p=29}}</ref> It was claimed that she died at 1&nbsp;p.m., but other sources suggest she died some hours later.<ref name="Fuller 2014 92–121"/> Depending on the source, Martha was between 17 and 29 years old at the time of her death, although 29 is the generally accepted figure.<ref name=Schorger30>{{Harvnb|Schorger|1955|p=30}}</ref> At the time, it was suggested that Martha might have died from an [[apoplexy|apoplectic stroke]], as she had suffered one a few weeks before dying.<ref name=ElPaso>{{cite news |title=Last Passenger Pigeon Dies |newspaper=[[El Paso Times |El Paso Morning Times]] |location=El Paso, Texas |page=6 |date=September 14, 1914 |url=https://texashistory.unt.edu/ark:/67531/metapth197161/m1/6/zoom/}}</ref> Her body was frozen into a block of ice and sent to the [[Smithsonian Institution]] in Washington, where it was skinned, dissected, photographed, and mounted.<ref name=Shufeldt/><ref name=Yeoman>{{cite web |last1=Yeoman |first1=B. |title=Why the Passenger Pigeon Went Extinct |website=[[Audubon (magazine) |Audubon Magazine]] |year=2014 |url=https://www.audubon.org/magazine/may-june-2014/why-passenger-pigeon-went-extinct |access-date=October 8, 2024 |url-status=live |archive-url=https://web.archive.org/web/20150121163434/http://www.audubonmagazine.org/articles/birds/why-passenger-pigeon-went-extinct |archive-date=January 21, 2015}}</ref> As she was [[molting]] when she died, she proved difficult to stuff, and previously shed feathers were added to the skin. Martha was on display for many years, but after a period in the museum vaults, she was put back on display at the Smithsonian's [[National Museum of Natural History]] in 2015.<ref name="Fuller 2014 92–121"/> A memorial statue of Martha stands on the grounds of the Cincinnati Zoo, in front of the "Passenger Pigeon Memorial Hut", formerly the aviary wherein Martha lived, now a [[National Historic Landmark]]. Incidentally, the last specimen of the extinct [[Carolina parakeet]], named "Incus," died in Martha's cage in 1918; the stuffed remains of that bird are exhibited in the "Memorial Hut".<ref name="SI"/><ref name="r4">{{cite web |title=Martha – Passenger Pigeon Memorial Hut |location=Cincinnati, Ohio |website=[[Roadside America]] |url=https://www.roadsideamerica.com/story/10663 |access-date=February 29, 2012}}</ref>

===Extinction causes===
[[File:Martha, the last Passenger Pigeon. Natural History Museum, June, 2015. Digital photo, cropped and brightened.jpg|upright|thumb|left|Martha at the [[Smithsonian Museum]], 2015]]

The main reasons for the extinction of the passenger pigeon were the massive scale of hunting, the rapid loss of habitat, and the extremely social lifestyle of the bird, which made it highly vulnerable to the former factors. [[Deforestation]] was driven by the need to free land for agriculture and expanding towns, but also due to the demand for lumber and fuel. About 728,000&nbsp;km<sup>2</sup> (180 million acres) were cleared for farming between 1850 and 1910. Though there are still large woodland areas in eastern North America, which support a variety of wildlife, it was not enough to support the vast number of passenger pigeons needed to sustain the population. In contrast, very small populations of nearly extinct birds, such as the [[kākāpō]] (''Strigops habroptilus'') and the [[takahē]] (''Porphyrio hochstetteri''), have been enough to keep those species extant to the present. The combined effects of intense hunting and deforestation has been referred to as a "[[Blitzkrieg]]" against the passenger pigeon, and it has been labeled one of the greatest and most senseless human-induced extinctions in history.<ref name="Fuller 2014 72–88"/><ref name="Hung 2014"/><ref name="Hume 2015"/> As the flocks dwindled in size, the passenger pigeon population decreased below the threshold necessary to propagate the species,<ref>{{cite journal |last1=Halliday |first1=T. |title=The extinction of the passenger pigeon ''Ectopistes migratorius'' and its relevance to contemporary conservation |journal=[[Biological Conservation (journal) |Biological Conservation]] |volume=17 |issue=2 |pages=157–162 |year=1980 |bibcode=1980BCons..17..157H |doi=10.1016/0006-3207(80)90046-4}}</ref> an example of the [[Allee effect]].<ref>{{cite web |title=Passenger Pigeon/Allee effect |website=kevintshoemaker.github.io |url=https://kevintshoemaker.github.io/NRES-470/LECTURE5.html |access-date=2020-09-25}}</ref>

[[File:Passenger pigeon shooting in Iowa.jpg|thumb|Pigeons being shot to save crops in Iowa, 1867]]
The 2014 genetic study that found natural fluctuations in population numbers prior to human arrival also concluded that the species routinely recovered from lows in the population, and suggested that one of these lows may have coincided with the intensified hunting by humans in the 1800s, a combination which would have led to the rapid extinction of the species. A similar scenario may also explain the rapid extinction of the [[Rocky Mountain locust]] (''Melanoplus spretus'') during the same period.<ref name="Hung 2014"/> It has also been suggested that after the population was thinned out, it would be harder for few or solitary birds to locate suitable feeding areas.<ref name="Extinct Birds"/> In addition to the birds killed or driven away by hunting during breeding seasons, many nestlings were also orphaned before being able to fend for themselves. Other, less convincing contributing factors have been suggested at times, including mass drownings, [[Newcastle disease]], and migrations to areas outside their original range.<ref name="iucn status 19 November 2021"/><ref name="Fuller 2014 72–88"/>

The extinction of the passenger pigeon aroused public interest in the [[conservation movement]], and resulted in new laws and practices which prevented many other species from becoming extinct.<ref name="SI"/> The rapid decline of the passenger pigeon has influenced later assessment methods of the extinction risk of endangered animal populations. The [[International Union for Conservation of Nature]] (IUCN) has used the passenger pigeon as an example in cases where a species was declared "at risk" for extinction even though population numbers are high.<ref name=ext/>

Naturalist [[Aldo Leopold]] paid tribute to the vanished species in a monument dedication held by the Wisconsin Society for Ornithology at [[Wyalusing State Park]], [[Wisconsin]], which had been one of the species' social roost sites.<ref>{{cite web |title=Passenger Pigeon Monument |date=December 2003 |publisher=Wisconsin Historical Society |url=https://www.wisconsinhistory.org/Records/Image/IM34684 |access-date=October 8, 2024}}</ref> Speaking on May 11, 1947, Leopold remarked:
{{Blockquote|Men still live who, in their youth, remember pigeons. Trees still live who, in their youth, were shaken by a living wind. But a decade hence only the oldest oaks will remember, and at long last only the hills will know.<ref name="Leopold">{{cite book |title=[[A Sand County Almanac]]: And Sketches Here and There |last=Leopold |first=Aldo |orig-date=1949 |year=1989 |publisher=[[Oxford University Press]] |location=[[New York City |New York]] |isbn=0-19-505928-X |page=109}}</ref>}}

===Potential resurrection of the species===
[[File:Ectopistes migratorius ULaval 2.jpg|thumb|Taxidermied male and female, [[Laval University]] Library]]
Today, at least 1,532 passenger pigeon skins (along with 16 skeletons) still exist, spread across many institutions all over the world.<ref name=Greenway>{{cite book |last=Greenway |first=J. C. |title=Extinct and Vanishing Birds of the World |publisher=American Committee for International Wild Life Protection 13 |location=New York |year=1967 |pages=304{{ndash}}311 |isbn=978-0-486-21869-4}}</ref><ref name="Aberrant"/> It has been suggested that the passenger pigeon should be revived when available technology allows it (a concept which has been termed "[[de-extinction]]"), using genetic material from such specimens. In 2003, the [[Pyrenean ibex]] (''Capra pyrenaica pyrenaica'', a subspecies of the [[Iberian ibex]]) was the first extinct animal to be cloned back to life; the clone lived for only seven minutes before dying of lung defects.<ref name="back to life"/><ref>{{cite web |title='Bringing Back the Passenger Pigeon' Meeting convened at Harvard Medical School in Boston |website=[[Long Now Foundation]] |date=2013-02-07 |url=http://longnow.org/revive/passenger-pigeon-workshop/ |access-date=April 10, 2015}}</ref> A hindrance to cloning the passenger pigeon is the fact that the DNA of museum specimens has been contaminated and fragmented, due to exposure to heat and oxygen. American geneticist [[George M. Church]] has proposed that the passenger pigeon genome can be reconstructed by piecing together DNA fragments from different specimens. The next step would be to splice these genes into the [[stem cell]]s of rock pigeons (or [[band-tailed pigeon]]s), which would then be transformed into egg and sperm cells, and placed into the eggs of rock pigeons, resulting in rock pigeons bearing passenger pigeon sperm and eggs. The offspring of these would have passenger pigeon traits, and would be further bred to favor unique features of the extinct species.<ref name="back to life"/><ref name="NatGeo 2013">{{cite web |last=Zimmer |first=C. |title=Bringing them back to life |website=National Geographic |year=2013 |url=http://ngm.nationalgeographic.com/2013/04/125-species-revival/zimmer-text |access-date=October 29, 2015 |archive-url=https://web.archive.org/web/20161212002128/http://ngm.nationalgeographic.com/2013/04/125-species-revival/zimmer-text |archive-date=December 12, 2016}}</ref><ref>{{cite web |last1=Landers |first1=J. |title=Scientists look to revive the long-extinct passenger pigeon |newspaper=[[The Washington Post]] |year=2013 |url=https://www.washingtonpost.com/national/health-science/scientists-look-to-revive-the-long-extinct-passenger-pigeon/2013/07/08/3d1323d4-b9a1-11e2-aa9e-a02b765ff0ea_story.html |access-date=November 6, 2014}}</ref> The American non-profit organization [[Revive & Restore]] is currently pursuing the idea.<ref>{{cite web |title=The Great Passenger Pigeon Comeback |language=en-US |url=https://reviverestore.org/about-the-passenger-pigeon/ |access-date=2023-08-10}}</ref>

The general idea of re-creating extinct species has been criticized, since the large funds needed could be spent on conserving currently threatened species and habitats, and because conservation efforts might be viewed as less urgent. In the case of the passenger pigeon, since it was very social, it is unlikely that enough birds could be created for revival to be successful, and it is unclear whether there is enough appropriate habitat left for its reintroduction. Furthermore, the parent pigeons that would raise the cloned passenger pigeons would belong to a different species, with a different way of rearing young.<ref name="back to life">{{cite web |last=Lewis |first=T. |website=NBC News |title=How to bring extinct animals back to life |year=2013 |url=https://www.nbcnews.com/science/how-bring-extinct-animals-back-life-8C10995683 |access-date=August 25, 2013}}</ref><ref name="NatGeo 2013"/>

==Bibliography==

===Notes===
{{Reflist|group=upper-alpha}}

===References===
{{Reflist}}

==External links==
{{Commons|Ectopistes migratorius}}
{{Wikispecies|Ectopistes migratorius}}
* [https://passengerpigeon.org/ Project Passenger Pigeon: Lessons from the Past for a Sustainable Future]
* [https://www.npr.org/2007/09/26/14722376/the-demise-of-the-passenger-pigeon The Demise of the Passenger Pigeon] (as broadcast on [[National Public Radio]]'s ''[[Day to Day]]'')
* [https://naturalhistory.si.edu/research/vertebrate-zoology/birds/collections-overview/martha-last-passenger-pigeon 360-degree view of Martha, the last passenger pigeon] ([[Smithsonian Institution]])

{{Columbimorphae Genera|C.|state=collapsed}}
{{Taxonbar|from=Q191968}}
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[[Category:1914 endings]]
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[[Category:Bird extinctions since 1500]]
[[Category:Birds described in 1766|passenger pigeon]]
[[Category:Columbidae]]
[[Category:Extinct animals of Canada]]
[[Category:Extinct animals of the United States]]
[[Category:Extinct birds of North America]]
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[[Category:Historical foods in American cuisine]]
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[[Category:Pleistocene first appearances]]
[[Category:Species made extinct by human activities]]
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[[Category:Animal taxa named by Carl Linnaeus|passenger pigeon]]