View source for Hippopotamus

{{Short description|Large semi-aquatic mammal native to sub-Saharan Africa}}
{{Redirect|Hippo|its genus|Hippopotamus (genus)|other uses|Hippopotamus (disambiguation)|and|Hippo (disambiguation)}}
{{pp-vandalism|small=yes}}
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{{Use British English|date=March 2022}}
{{Use dmy dates|date=March 2022}}
{{Speciesbox
| italic_title = no
| name = Hippopotamus
| fossil_range = {{fossilrange|Pleistocene|Recent}}
| image = Portrait Hippopotamus in the water.jpg
| image_caption = A hippopotamus in [[Saadani National Park]], Tanzania
| status = VU
| status_system = IUCN3.1
| status_ref = <ref name=iucn>{{cite iucn |author=Lewison, R. |author2=Pluháček, J. |date=2017 |title=''Hippopotamus amphibius'' |article-number=e.T10103A18567364 |doi=10.2305/IUCN.UK.2017-2.RLTS.T10103A18567364.en |access-date=19 November 2021}}</ref>
| status2 = CITES_A2
| status2_system = CITES
| status2_ref = <ref name=iucn/>
| genus = Hippopotamus
| species = amphibius
| authority = [[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]]<ref name=Linnæus>{{cite book |author=Linnæus, C. |year=1758 |title=Caroli Linnæi Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis |publisher=Salvius |location=Holmiae |chapter=''Hippopotamus amphibius'' |page=74 |chapter-url=https://archive.org/details/mobot31753000798865/page/n87/mode/2up}}</ref>
| range_map = Hippopotamus_distribution.png
| range_map_caption = Current distribution of the hippopotamus
}}
The '''hippopotamus''' ('''''Hippopotamus amphibius''';'' {{IPAc-en|ˌ|h|ɪ|p|ə|ˈ|p|ɒ|t|ə|m|ə|s}}; {{plural form}}: '''hippopotamuses'''), often shortened to '''hippo''' ({{plural form}}: '''hippos'''), further qualified as the '''common hippopotamus''', '''Nile hippopotamus''' and '''river hippopotamus''', is a large [[semiaquatic]] [[Mammal|mammal]] native to [[sub-Saharan Africa]]. It is one of only two [[extant taxon|extant]] [[species]] in the [[scientific classification|family]] [[Hippopotamidae]], the other being the [[pygmy hippopotamus]] (''Choeropsis liberiensis'' or ''Hexaprotodon liberiensis''). Its name comes from the [[Ancient Greek]] for "river horse" ({{lang|grc|ἱπποπόταμος}}).

After [[elephant]]s and [[rhinoceros]]es, the hippopotamus is the next [[Largest mammals#Even-toed Ungulates (Artiodactyla)|largest land mammal]]. It is also the largest extant land [[artiodactyl]]. Despite their physical resemblance to [[pig]]s and other terrestrial even-toed ungulates, the closest living relatives of the hippopotamids are [[cetacea]]ns ([[whale]]s, [[dolphin]]s, [[porpoise]]s, etc.), from which they diverged about 55 million years ago. Hippos are recognisable for their barrel-shaped torsos, wide-opening mouths with large [[Canine tooth|canine]] tusks, nearly hairless bodies, short legs, and large size: adults average {{cvt|1500|kg}} for bulls (males) and {{cvt|1300|kg|}} for cows (females).

Hippos inhabit rivers, lakes, and [[mangrove]] swamps. [[Territorial animal|Territorial]] bulls each preside over a stretch of water and a group of five to thirty cows and calves. [[Mating]] and birth both occur in the water. During the day, hippos remain cool by staying in water or mud, emerging at dusk to graze on grasses. While hippos rest near each other in the water, grazing is a solitary activity and hippos typically do not display territorial behaviour on land. Hippos are among the most dangerous animals in the world due to their aggressive and unpredictable nature. They are threatened by [[habitat loss]] and [[poaching]] for their meat and [[ivory]] (canine teeth).

==Etymology==
The [[Latin]] word {{lang|la|hippopotamus}} is derived from the ancient [[Greek language|Greek]] {{lang|grc|ἱπποπόταμος}} ({{Transliteration|grc|hippopótamos}}), from {{lang|grc|ἵππος}} ({{Transliteration|grc|híppos}}) {{gloss|horse}} and {{lang|grc|ποταμός}} ({{Transliteration|grc|potamós}}) {{gloss|river}}, together meaning {{gloss|horse of the river}}.<ref>{{LSJ|i(ppopo/tamos|ἱπποπόταμος}}, {{LSJ|i(/ppos|ἵππος}}, {{LSJ|potamo/s|ποταμός|ref}}.</ref><ref>{{cite encyclopedia|url=https://www.merriam-webster.com/dictionary/hippopotamus|title=Hippopotamus|dictionary= [[Webster's Dictionary|Merriam-Webster's Online Dictionary]]|access-date=18 July 2007}}</ref><ref>{{OEtymD|hippopotamus}}</ref> In English, the [[English plural|plural]] is "hippopotamuses".<ref>{{cite encyclopedia|url=http://www.askoxford.com/asktheexperts/faq/aboutgrammar/plurals?view=uk|title=Plural of hippopotamus|dictionary=[[Oxford English Dictionary]]|access-date=18 July 2007|archive-date=13 October 2008|archive-url=https://web.archive.org/web/20081013041855/http://www.askoxford.com/asktheexperts/faq/aboutgrammar/plurals?view=uk}}</ref>

==Taxonomy and origins==

===Classification===
{{multiple image
 | direction         = vertical
 | image1 = Hipopótamo (Hippopotamus amphibius), parque nacional de Chobe, Botsuana, 2018-07-28, DD 60.jpg
|alt1=Closeup photo, top of head, feeding while partially submerged
 | image2            = Hippopotamus amphibius 3d scan Natural History Museum University of Pisa C 228.stl
|alt2=Interactive 3D partial skull scan
 | image3            = Hippopotamus amphibius (mandible) 3d scan Natural History Museum University of Pisa C228.stl
|alt3=Interactive 3D scan of the remaining mandible
 | footer            = Head, skull and mandible of ''Hippopotamus amphibius''
}}
The modern hippopotamus and the [[pygmy hippopotamus]] are the only living members of the family Hippopotamidae. Some taxonomists place hippos and [[anthracotheres]] in the superfamily Anthracotheroidea. Hippopotamidae are classified along with other [[even-toed ungulates]] in the [[order (biology)|order]] [[Artiodactyla]].<ref name="The Hippos"/>{{rp|39–40}}

Five subspecies of hippos have been described based on [[morphology (biology)|morphological]] differences in their skulls as well as differences in geographical range:<ref name="The Hippos"/>{{rp|3}}<ref>{{cite book|author=Lydekker, R|year=1915|title=Catalogue of the Ungulate Mammals in the British Museum of Natural History, vol. 4|volume=4 |publisher=British Museum|pages=389–392|url=https://www.biodiversitylibrary.org/item/114771#page/417/mode/1up}}</ref><ref name="Okello"/><ref>{{Cite journal|title = Suiform Soundings: The IUCN/SSC Pigs, Peccaries, and Hippos Specialist Group (PPHSG) Newsletter|volume = 5|issue = 1|date=September 2005|url = https://www.scribd.com/document/65917875/Newsletter-5-1 |format=PDF |journal = [[World Conservation Union|IUCN]]|editor = Meijaard, Erik}}</ref>
*''H. a. amphibius'' – (the nominate subspecies) ranges from [[Gambia]] east to [[Ethiopia]] and then south to [[Mozambique]] and historically ranged as far north as Egypt; its skull is distinguished by a moderately reduced preorbital region, a bulging dorsal surface, elongated [[mandibular symphysis]] and larger chewing teeth.
*''H. a. kiboko'' – found in [[Kenya]] and [[Somalia]]; was noted to be smaller and more lightly coloured than other hippos with wider nostrils, somewhat longer snout and more rounded and relatively raised [[Orbit (anatomy)|orbit]]s with the space between them being incurved.
*''H. a. capensis'' – found in [[Zambia]] and [[South Africa]]; distinguished by wider orbits.
*''H. a. tschadensis'' – ranges between [[Chad]] and [[Niger]]; featured a slightly shorter but broader face, and pronounced, forward-facing orbits.
*''H. a. constrictus'' – ranges from the southern [[Democratic Republic of Congo]] to [[Angola]] and [[Namibia]]; skull characterised by a thicker preorbital region, shorter snout, flatter dorsal surface, reduced mandibular symphysis and smaller chewing teeth.
The suggested subspecies above were never widely used or validated by field biologists; the described morphological differences were small enough that they could have resulted from simple variation in nonrepresentative samples.<ref name="The Hippos">{{cite book |last=Eltringham |first=S. K. |title=The Hippos: Natural History and Conservation |year=1999 |publisher=Academic Press |isbn=978-0-85661-131-5 |series=Poyser Natural History Series}}</ref>{{rp|2}} A study examining [[mitochondrial DNA]] from skin biopsies taken from 13 sampling locations found "low, but significant, genetic differentiation" among ''H. a. amphibius'', ''H. a. capensis'', and ''H. a. kiboko''. Neither ''H. a. tschadensis'' nor ''H. a. constrictus'' have been tested.<ref name=Okello>{{Cite journal |author=Okello, J. B. A. |author2=Nyakaana, S. |author3=Masembe, C. |author4=Siegismund, H. R. |author5=Arctander, P. |year=2005 |title=Mitochondrial DNA variation of the common hippopotamus: evidence for a recent population expansion |journal=[[Heredity (journal)|Heredity]] |pmid=16030528 |volume =95 |issue=3 |pages=206–215 |doi=10.1038/sj.hdy.6800711 |doi-access=free|bibcode=2005Hered..95..206O }}</ref>

===Evolution===
[[File:Evolutionary relationships among laurasiatherian mammals as used in molecular evolution analyses.jpg|thumb|Evolutionary relationships among hippo and Cetacea (whales, dolphins)<ref name="TsagkogeorgaMcGowen2015">{{cite journal |last1=Tsagkogeorga |first1=G. |last2=McGowen |first2=M. R. |last3=Davies |first3=K. T. J.|last4=Jarman |first4=S. |last5=Polanowski |first5=A. |last6=Bertelsen |first6=M. F. |last7=Rossiter |first7=S. J. |title=A phylogenomic analysis of the role and timing of molecular adaptation in the aquatic transition of cetartiodactyl mammals |journal=Royal Society Open Science |volume=2 |issue=9 |year=2015 |article-number=150156 |doi=10.1098/rsos.150156 |pmid=26473040 |pmc=4593674 |bibcode=2015RSOS....250156T}}</ref>]]
Until 1909, [[natural history|naturalists]] classified hippos together with pigs based on [[molar (tooth)|molar]] patterns. Several lines of evidence, first from blood proteins, then from [[molecular systematics]],<ref name=Genomes/> [[DNA]]<ref name=DNA>{{Cite journal |title=More DNA support for a Cetacea/Hippopotamidae clade: the blood-clotting protein gene gamma-fibrinogen |author=Gatesy, J. |journal=[[Molecular Biology and Evolution]] |date=1997 |volume=14 |pages=537–543 |pmid=9159931 |issue=5 |doi=10.1093/oxfordjournals.molbev.a025790 |doi-access=free}}</ref><ref name=Nature2009>{{Cite journal |title=Hippopotamus and whale phylogeny |author1=Geisler, J. H. |author2=Theodor, J. M. |journal=[[Nature (journal)|Nature]] |year=2009 |pmid=19295550 |volume=458 |doi=10.1038/nature07776 |bibcode=2009Natur.458....1G |issue=7236 |pages=E1–E4; discussion E5 |s2cid=4320261}}</ref> and the [[fossil record]], show their closest living relatives are [[cetacean]]s ([[whale]]s, [[dolphin]]s, and [[porpoise]]s).<ref name=ScienceNews>{{cite web |first=R. |last=Sanders |title=Scientists find missing link between the dolphin, whale and its closest relative, the hippo |date=2005 |archive-url= https://web.archive.org/web/20150226060713/http://www.innovations-report.com//html/reports/life-sciences/report-39309.html |archive-date= 26 February 2015 |url-status=live |access-date=8 January 2011 |url=https://www.innovations-report.com/html/reports/life_sciences/report-39309.html |work=Science News Daily}}</ref><ref name=Cetartiodactyla/> The common ancestor of hippos and whales branched off from [[Ruminantia]] and the rest of the even-toed ungulates; the cetacean and hippo lineages split soon afterwards.<ref name="DNA"/><ref name=Cetartiodactyla>{{cite journal |author1=Boisserie, J.-R. |author2=Lihoreau, F. |author3=Brunet, M. |year=2005 |title=The position of Hippopotamidae within Cetartiodactyla |journal=[[Proceedings of the National Academy of Sciences]] |volume=102 |issue=5 |pages=1537–1541 |doi=10.1073/pnas.0409518102 |pmid=15677331 |pmc=547867 |bibcode=2005PNAS..102.1537B |doi-access=free}}</ref>

{{Cetartiodactyla Cladogram}}
[[File:Anthracotherium magnum.jpg|thumb|right|''[[Anthracotherium]] magnum'' from the Oligocene of Europe]]
The most recent theory of the origins of Hippopotamidae suggests hippos and whales shared a common semiaquatic ancestor that branched off from other artiodactyls around {{mya|60|million years ago}}.<ref name=DNA/><ref name=ScienceNews/> This hypothesised ancestral group likely split into two branches again around {{mya|54|million years ago}}.<ref name=Genomes>{{Cite journal |title=Analyses of mitochondrial genomes strongly support a hippopotamus-whale clade |volume=265 |issue=1412 |year=1998 |journal=[[Proceedings of the Royal Society]] |pmid=9881471 |author1=Ursing, B. M. |author2=Arnason U. |pmc=1689531 |doi=10.1098/rspb.1998.0567 |pages=2251–2255}}</ref>

One branch would [[Evolution of cetaceans|evolve into cetaceans]], possibly beginning about {{mya|52|million years ago}}, with the protowhale ''[[Pakicetus]]'' and other early whale ancestors collectively known as [[Archaeoceti]]. This group eventually underwent [[aquatic adaptation]] into the completely aquatic [[cetacea]]ns.<ref name=Cetartiodactyla/> The other branch became the [[anthracotheriidae|anthracotheres]], a large family of four-legged beasts, the earliest of which in the late [[Eocene]] would have resembled skinny hippos with comparatively smaller, narrower heads. All branches of the anthracotheres, except that which evolved into [[Hippopotamidae]], became extinct during the [[Pliocene]], leaving no descendants.<ref name=ScienceNews/><ref name=Cetartiodactyla/>

A rough evolutionary lineage of the hippo can thus be traced from Eocene and [[Oligocene]] species: from ''[[Anthracotherium]]'' and ''[[Elomeryx]]'' to the [[Miocene]] species ''[[Merycopotamus]]'' and ''[[Libycosaurus]]'' and finally the very latest anthracotheres in the [[Pliocene]].<ref name=Origins>{{cite journal |last=Boisserie |first=J.-R. |author2=Lihoreau, F. |author3=Brunet, M. |year=2005 |title=Origins of Hippopotamidae (Mammalia, Cetartiodactyla): towards resolution |journal=[[Zoologica Scripta]] |volume=34 |issue=2 |pages=119–143 |doi=10.1111/j.1463-6409.2005.00183.x |s2cid=83768668}}</ref> These groups lived across Eurasia and Africa. The discovery of ''Epirigenys'' in East Africa, which was likely a descent of Asian anthracotheres and a [[sister taxon]] to Hippopotamidae, suggests that hippo ancestors entered Africa from Asia around {{Mya|35|million years ago}}.<ref>{{cite journal|author1=Lihoreau, F. |author2=Boisserie, J.-R. |author3=Manthi, F. K. |author4=Ducrocq. S. |year=2015 |title=Hippos stem from the longest sequence of terrestrial cetartiodactyl evolution in Africa |journal=Nature Communications |volume=6 |article-number=6264 |doi=10.1038/ncomms7264 |pmid=25710445 |bibcode=2015NatCo...6.6264L |doi-access=free}}</ref><ref>{{cite web |author=Lihoreau, F. |date=2015 |title=New Fossils from Kenya Precise Hippo Origin |publisher=Serious Science |access-date=5 June 2021|url=http://serious-science.org/new-fossils-from-kenya-precise-hippo-origin-2675}}</ref> An early hippopotamid is the genus ''[[Kenyapotamus]]'', which lived in Africa from 15 to {{mya|9|million years ago}}.<ref name=Origins/> Hippopotamid species would spread across Africa and Eurasia, including the modern pygmy hippo. From 7.5 to {{mya|1.8|million years ago}}, a possible ancestor to the modern hippo, ''[[Archaeopotamus]]'', lived in Africa and the Middle East.<ref name=Linnean>{{cite journal |last=Boisserie |first=J.-R. |year=2005 |title=The phylogeny and taxonomy of Hippopotamidae (Mammalia: Artiodactyla): a review based on morphology and cladistic analysis |journal=[[Zoological Journal of the Linnean Society]] |volume=143 |pages=1–26 |doi=10.1111/j.1096-3642.2004.00138.x |doi-access=free}}</ref> The oldest records of the genus ''[[Hippopotamus (genus)|Hippopotamus]]'' date to the [[Pliocene]] (5.3–2.6 million years ago).<ref name=VanDerMadeEtAl2017/> The oldest unambiguous records of the modern ''H. amphibius'' date to the [[Middle Pleistocene]], though there are possible [[Early Pleistocene]] records.<ref>{{Cite journal |last1=Pandolfi |first1=L. |last2=Martino |first2=R. |last3=Belvedere |first3=M. |last4=Martínez-Navarro |first4=B. |last5=Medin |first5=T. |last6=Libsekal |first6=Y. |last7=Rook |first7=L. |date=2023 |title=The latest Early Pleistocene hippopotami from the human-bearing locality of Buia (Eritrea) |journal=Quaternary Science Reviews |volume=308 |article-number=108039 |doi=10.1016/j.quascirev.2023.108039|bibcode=2023QSRv..30808039P |s2cid=258024770}}</ref>
[[File:Malagasy Hippopotamus.jpg|thumb|right|''Choeropsis madagascariensis'' skeleton with a modern hippopotamus skull]]

===Extinct species===
Three species of [[Malagasy hippopotamus]] became extinct during the [[Holocene]] on [[Madagascar]], the last of them within the past 1,000 years. The Malagasy hippos were smaller than the modern hippo, likely a result of the process of [[insular dwarfism]].<ref name=Stuenes>{{Cite journal |doi=10.1080/02724634.1989.10011761 |author=Stuenes, S. |year=1989 |title=Taxonomy, habits and relationships of the sub-fossil Madagascan hippopotamuses ''Hippopotamus lemerlei'' and ''H. madagascariensis'' |journal=[[Journal of Vertebrate Paleontology]] |volume=9 |pages=241–268 |issue=3}}</ref> Fossil evidence indicates many Malagasy hippos were hunted by humans, a factor in their eventual extinction.<ref name=Stuenes/> Isolated individual Malagasy hippos may have survived in remote pockets; in 1976, villagers described a living animal called the ''kilopilopitsofy'', which may have been a Malagasy hippo.<ref name=Kidoky>{{Cite journal |title=The Kilopilopitsofy, Kidoky, and Bokyboky: Accounts of Strange Animals from Belo-sur-mer, Madagascar, and the Megafaunal "Extinction Window" |journal=[[American Anthropologist]] |year=1998 |author=Burney, D. A. |jstor=681820 |volume=100 |issue=4 |pages=957–966 |author2=Ramilisonina |doi=10.1525/aa.1998.100.4.957}}</ref>

''[[Hippopotamus gorgops]]'' from the Early Pleistocene to the early Middle Pleistocene of Africa and West Asia grew considerably larger than the living hippopotamus, with an estimated body mass of over {{Cvt|4000|kg}}.<ref name=VanDerMadeEtAl2017>van der Made J, Sahnouni M & Boulaghraief K. 2017. [https://www.mncn.csic.es/sites/default/files/inline-files/2017%20Van%20der%20Made%20ea%20-%20Hippopotamus%20-%20El%20Kherba%20-%20ProcIIMeetingAfrPrehist.pdf ''Hippopotamus gorgops'' from El Kherba (Algeria) and the context of its biogeography]. In Proceedings of the II Meeting of African Prehistory: Burgos 15–16 April 2015, Sahnouni M, Semaw S, Rios Garaizar J (eds). CENIEH: Burgos; 135–169.</ref><ref>Chaix L, Faure M, Guérin C, Honegger M. [https://kerma.ch/documents/Publications_PDF/Chaix_Faure_Guerin_Honegger_Kaddanarti_2000.pdf Kaddanarti, a Lower Pleistocene Assemblage from Northern Sudan]. In: Krzyżaniak L, Kroeper K, Kobusiewicz M, editors. Recent Research into the Stone Age of Northeastern Africa. Poznań: Poznań Archaeological Museum; 2000. p. 33–46.</ref><ref>{{Cite journal |last=Hutchinson |first=J. R. |date=2021 |title=The evolutionary biomechanics of locomotor function in giant land animals |journal=Journal of Experimental Biology |volume=224 |issue=11 |article-number=jeb217463 |doi=10.1242/jeb.217463 |issn=0022-0949 |pmc=8214834 |pmid=34100541|bibcode=2021JExpB.224B7463H }}</ref> ''[[Hippopotamus antiquus]]'' ranged throughout Europe, extending as far north as Britain during the [[Early Pleistocene|Early]] and [[Middle Pleistocene]] epochs, before being replaced by the modern ''H. amphibius'' in Europe during the latter part of the Middle Pleistocene.<ref>{{Cite journal |last1=Adams|first1=N. F. |last2=Candy |first2=I. |last3=Schreve |first3=D. C.|title=An Early Pleistocene hippopotamus from Westbury Cave, Somerset, England: support for a previously unrecognized temperate interval in the British Quaternary record |journal=Journal of Quaternary Science |year=2022 |volume=37 |issue=1 |pages=28–41 |doi=10.1002/jqs.3375 |bibcode=2022JQS....37...28A |s2cid=244179438 |doi-access=free}}</ref> The Pleistocene also saw a number of dwarf species evolve on several Mediterranean islands, including [[Crete]] (''[[Hippopotamus creutzburgi]]''), [[Cyprus]] (the [[Cyprus dwarf hippopotamus]], ''Hippopotamus minor''), [[Malta]] (''[[Hippopotamus melitensis]]''), and [[Sicily]] (''[[Hippopotamus pentlandi]]''). Of these, the Cyprus dwarf hippo survived until the end of the Pleistocene or early Holocene. Evidence from the archaeological site [[Aetokremnos]] continues to cause debate on whether or not the species was driven to extinction or even encountered by humans.<ref>{{Cite journal |author=Simmons, A. |year=2000 |title=Faunal extinction in an island society: pygmy hippopotamus hunters of Cyprus |journal=[[Geoarchaeology]] |volume=15 |issue=4 |pages=379–381 |doi=10.1002/(SICI)1520-6548(200004)15:4<379::AID-GEA7>3.0.CO;2-E |bibcode=2000Gearc..15..379G}}</ref><ref name="Taxonomy of Pleistocene">{{cite journal |author=Petronio, C. |year=1995 |title=Note on the taxonomy of Pleistocene hippopotamuses |journal=Ibex |volume=3 |pages=53–55  |url=http://www.mountainecology.org/IBEX3/pdf/Art_Capitolo1/note_taxonomy_pleistocene.pdf |archive-url=https://web.archive.org/web/20080912012236/http://www.mountainecology.org/IBEX3/pdf/Art_Capitolo1/note_taxonomy_pleistocene.pdf|archive-date=12 September 2008}}</ref>

==Characteristics==
[[File:Hippo skull dark.jpg|thumb|Hippopotamus [[skull]], showing the large canines and incisors used for fighting]]
The hippopotamus is a [[megaherbivore]] and is the third largest land mammal after [[elephant]]s and some [[rhinoceros]] species. The mean adult weight is around {{cvt|1480|kg}} for bulls and {{cvt|1365|kg}} for cows. Exceptionally large males have been recorded reaching {{cvt|2660|kg}}.<ref name="Owen-Smith_1992">{{cite book|last1=Owen-Smith|first1=R. N. |title=Megaherbivores: The Influence of Very Large Body Size on Ecology |date=1992 |pages=6–14|publisher=Cambridge University Press|isbn=978-0-521-42637-4}}</ref> Male hippos appear to continue growing throughout their lives, while females reach maximum weight at around age 25.<ref>{{Cite journal |author1=Marshall, P. J. |author2=Sayer, J. A. |title=Population ecology and response to cropping of a hippo population in eastern Zambia |jstor=2401788 |volume=13 |issue=2 |year=1976 |journal=The Journal of Applied Ecology |pages=391–403 |doi=10.2307/2401788}}</ref> It is {{cvt|2.90|to|5.05|m}} long,<ref>{{cite web |url=http://animaldiversity.ummz.umich.edu/site/accounts/information/Hippopotamus_amphibius.html#physical_description|title = Physical Description |access-date=2020-10-22}}</ref> including a tail of about {{cvt|35|to|56|cm}} in length and {{cvt|1.30|to|1.65|m}} tall at the shoulder,<ref>{{cite web|url=http://www.ultimateungulate.com/artiodactyla/hippopotamus_amphibius.html|title = ''Hippopotamus amphibius''|access-date=2020-10-22}}</ref><ref name="Hippopotamus">{{cite web|url=http://sarkive.com/mammals/hippopotamus-amphibius/|title=Hippopotamus|access-date=2020-10-22|archive-date=8 August 2020|archive-url=https://web.archive.org/web/20200808175302/http://sarkive.com/mammals/hippopotamus-amphibius/}}</ref> with males and females ranging {{cvt|1.40|to|1.65|m}} and {{cvt|1.30|to|1.45|m}} tall at the shoulder respectively.<ref name="Hippopotamus"/> The species has a typical head–body length of {{cvt|3.3|–|3.45|m}} and an average standing height of {{cvt|1.4|m}} at the shoulder.<ref>{{Cite book|title=The Encyclopedia of Mammals|publisher=[[Oxford University Press]]|year=2001|isbn=978-0-7607-1969-5 |edition=2nd |page=491 |author=Eltringham, S. K.|contribution=Hippopotamuses|editor=MacDonald, D.}}</ref>

Hippos have barrel-shaped bodies with short tails and legs, and an hourglass-shaped skull with a long snout.<ref name=estes/><ref name="The Hippos"/>{{rp|3, 19}} Their skeletal structures are [[wikt:graviportal|graviportal]], adapted to carrying their enormous weight,<ref name="The Hippos"/>{{rp|8}} and their dense bones and low [[centre of gravity]] allows them to sink and move along the bottom of the water.<ref>{{cite journal|author1=Coughlin, B. L.|author2=Fish, F. E.|year=2009 |title=Hippopotamus underwater locomotion: Reduced-gravity movements for a massive mammal |journal=Journal of Mammalogy|volume=90|issue=3|pages=675–679|doi=10.1644/08-MAMM-A-279R.1 |s2cid=51686926 |doi-access=free}}</ref> Hippopotamuses have small legs (relative to other [[megafauna]]) because the water in which they live reduces the weight burden.<ref>{{cite book|title=Exploring Mammals|publisher=Marshall Cavendish Corporation |page=616 |url=https://books.google.com/books?id=k8o0HTqvwH0C&q=hippo+legs+water&pg=PA616 |isbn=978-0-7614-7728-0 |year=2008}}</ref> The toes are webbed and the [[pelvis]] rests at an angle of 45 degrees.<ref name="The Hippos"/>{{rp|3, 9}} Though chubby-looking, hippos have little fat.<ref name="The Hippos"/>{{rp|3}} The eyes, ears, and nostrils of hippos are placed high on the roof of their skulls. This allows these organs to remain above the surface while the rest of the body is submerged.<ref name=kingdon/>{{rp|259}} The nostrils and ears can close when underwater while [[nictitating membrane]]s cover the eyes.<ref name="The Hippos"/>{{rp|4, 116}} The [[vocal fold]]s of the hippo are more horizontally positioned, much like baleen whales. Underneath are throat tissues, where vibrations are transmitted to produce underwater calls.<ref>{{cite journal|last1=Reidenberg|first1=J. S. |year=2017|title=Terrestrial, semiaquatic, and fully aquatic mammal sound production mechanisms |journal=Acoustics Today |volume=13|issue=2|pages=35–43 |url=https://acousticstoday.org/wp-content/uploads/2017/05/Reidenberg.pdf}}</ref>

[[File:Hipopótamos (Hippopotamus amphibius), parque nacional de Chobe, Botsuana, 2018-07-28, DD 79.jpg|thumb|Characteristic "yawn" of a hippo]]
The hippo's jaw powered by huge [[masseter muscle|masseter]] and [[digastric muscle]]s,<ref name=kingdon>{{Cite book|author=Kingdon, J. |year=1988|title=East African Mammals: An Atlas of Evolution in Africa |volume=((3, Part B: Large Mammals)) |pages=256–277|publisher=University Of Chicago Press |isbn=978-0-226-43722-4}}</ref>{{rp|259}} and the hinge is located far back enough so that they can open their mouths at 100–110 degrees.<ref name="The Hippos"/>{{rp|17}}<ref name=Herring+Herring1975/> Extensions at the back of the jaw create more surface area for muscle attachment, which gives them large, droopy cheeks<ref name="The Hippos"/>{{rp|19}} This allows them to achieve their gape without tearing any tissue.<ref>{{cite journal|author=Herring, S. W.|year=1975|title=Adaptations for gape in the hippopotamus and its relatives |journal=Forma et Functio |volume=8 |pages=85–100}}</ref><ref name=Herring+Herring1975>{{cite journal|last1=Herring|first1=S. W.|last2=Herring|first2=S. E.|year=1975|title=The superficial masseter and gape in mammals|journal=The American Naturalist|volume=108|issue=962|pages=561–576|doi=10.1086/282934 |jstor=2459686}}</ref> On the lower jaw, the [[incisor]]s and [[Canine tooth|canines]] grow continuously, the former reaching {{cvt|40|cm}}, while the latter can grow to up to {{cvt|50|cm}}. The lower canines are sharpened through contact with the smaller upper canines.<ref name=estes>{{Cite book |title=The Behavior Guide to African Mammals: including hoofed mammals, carnivores, primates |author=Estes, R. |publisher=University of California Press |pages=222–226 |year=1992 |isbn=978-0-520-08085-0 |url=https://archive.org/details/isbn_0520080858/page/222}}</ref> The canines and incisors are used mainly for combat instead of feeding,<ref name=kingdon/>{{rp|259}} and the jaws are too rigid for side to side motion, making them less efficient for chewing.<ref name=Avedik2023>{{cite journal|last1=Avedik|first1=A|last2=Clauss|first2=M|year=2023|title=Chewing, dentition and tooth wear in Hippopotamidae (''Hippopotamus amphibius'' and ''Choeropsis liberiensis'')|journal=PLOS ONE|volume=18|issue=10|article-number=e0291825|doi=10.1371/journal.pone.0291825|doi-access=free|pmid=37792716|pmc=10550173|bibcode=2023PLoSO..1891825A}}</ref> Hippos rely on their flattened, horny lips to grasp and pull grasses which are then passed to the [[Molar (tooth)|molars]],<ref name=kingdon/>{{rp|263}} which have complex [[Tooth enamel|enamel]] folds on their chewing surface.<ref name=Avedik2023/> The hippo is considered to be a [[pseudoruminant]]; it has a complex three-chambered stomach, but does not "chew [[cud]]".<ref name="The Hippos"/>{{rp|22}}
[[File:Hippopotamus in San Diego Zoo.jpg|thumb|Completely submerged hippo ([[San Diego Zoo]])]]

Hippo skin is {{cvt|6|cm}} thick across much of its body with little hair.<ref name=estes/><ref name=kingdon/>{{rp|260}} The animal is mostly purplish-grey or blue-black, but brownish-pink on the underside and around the eyes and ears.<ref name=kingdon/>{{rp|260}} Their skin secretes a natural, red-coloured [[sunscreen]] substance that is sometimes referred to as "blood sweat" but is neither blood nor sweat. This secretion is initially colourless and turns red-orange within minutes, eventually becoming brown. Two highly acidic pigments have been identified in the secretions; one red [[hipposudoric acid]] and one orange norhipposudoric acid, which inhibit the growth of disease-causing bacteria and their light-absorption profile peaks in the [[ultraviolet]] range, creating a sunscreen effect.<ref name="Distillations">{{cite journal |last1=Kean |first1=Sam |title=Sweating blood |url=https://www.sciencehistory.org/distillations/magazine/sweating-blood |journal=Distillations |date=2018|volume=4 |issue=2 |page=5 |access-date=20 August 2018}}</ref><ref name="Saikawa"/> Regardless of diet, all hippos secrete these pigments so food does not appear to be their source; rather, they may be synthesised from [[Protein precursor|precursors]] such as the [[amino acid]] [[tyrosine]].<ref name="Saikawa">{{cite journal|author=Saikawa, Y.|author2= Hashimoto, K.|author3= Nakata, M.|author4= Yoshihara, M.|author5= Nagai, K.|author6= Ida, M.|author7= Komiya, T. |title=Pigment chemistry: the red sweat of the hippopotamus|journal=[[Nature (journal)|Nature]] |volume=429 |issue=6990 |year=2004 |page=363 |pmid=15164051 |doi=10.1038/429363a |bibcode=2004Natur.429..363S |s2cid=4404922 |doi-access=free}}</ref> This natural sunscreen cannot prevent the animal's skin from cracking if it stays out of water too long.<ref>{{cite book|author=Jablonski, N. G.|year=2013 |title=Skin: A Natural History|publisher=University of California Press |page=34 |isbn=978-0-520-24281-4 |url=https://archive.org/details/skinnaturalhisto00jabl/page/34}}</ref>

The testes of the males do not fully descend and a scrotum is not present. In addition, the penis retracts into the body when not [[erection|erect]]. The genitals of the female hippos are unusual in that the vagina is ridged and the [[vulval vestibule]] has two large, protruding [[diverticula]]. Both of these have an unknown function.<ref name="The Hippos"/>{{rp|28–29}}

A hippo's lifespan is typically 40 to 50 years.<ref name=kingdon/>{{rp|277}} Donna the Hippo was one of the oldest living hippos in captivity. She lived at the [[Mesker Park Zoo]] in [[Evansville, Indiana]], in the US<ref>{{cite web |title=Oldest Hippo Turns 55! |url=http://www.evansvillecvb.org/media/index.tpl?ID=39&Display=Detail |publisher=[[Mesker Park Zoo]] |date=2006 |access-date=21 June 2007 |archive-url=https://web.archive.org/web/20070927120505/http://www.evansvillecvb.org/media/index.tpl?ID=39&Display=Detail |archive-date=27 September 2007}}</ref><ref>{{Cite news |url=http://www.courierpress.com/news/2007/jul/12/celebrate-with-donna |title=Celebrate with Donna |work=[[Evansville Courier & Press]] |access-date=15 July 2007 |date=2007 |archive-date=16 January 2014 |archive-url=https://web.archive.org/web/20140116201843/http://www.courierpress.com/news/2007/jul/12/celebrate-with-donna/ }}</ref> until her death in 2012 at the age of 61.<ref>{{cite web |author=Fears, D. |date=2012 |title=Goodbye, Donna: World's oldest hippo in captivity dies at 61 |publisher=Today.com|access-date=12 September 2013|url=http://www.today.com/pets/goodbye-donna-worlds-oldest-hippo-captivity-dies-61-922081 |archive-url=https://web.archive.org/web/20130604043252/http://www.today.com/pets/goodbye-donna-worlds-oldest-hippo-captivity-dies-61-922081 |archive-date=4 June 2013}}</ref> Two hippos share the record for the oldest hippo ever recorded at 65 years. Bertha, a female Hippo, who lived in the [[Manila Zoo]] in the Philippines since it first opened in 1959 until her death in July 2017, and <ref>{{Cite news |title=Bertha, the world's 'oldest' hippo, dies at 65 |url=https://www.bbc.com/news/world-asia-40558057 |work=BBC News |date=2017 |access-date=29 November 2020}}</ref> male Hippo Lu, from the Ellie Schiller [[Homosassa Springs Wildlife State Park]], who was born at the San Diego Zoo on January 26th, 1960, and died at Homosassa, where he died in June 2025, also at the age of 65.<ref>{{Cite web |last=<!-- not stated --> |date=2025-06-08 |title=Lu, Citrus County's celebrity hippo, dies at 65 |url=https://www.chronicleonline.com/news/local/lu-citrus-county-s-celebrity-hippo-dies-at-65/article_38cbe57c-5def-53ff-a563-d589cdd235d5.html |access-date=2025-06-09 |website=Chronicle Online 
|language=en}}</ref> Two other notably long-lived hippos were the female Tanga (1934{{ndash}}1995) at the [[Hellabrunn Zoo]] in [[Munich, Germany]] and male Blackie at the [[Cleveland Metroparks Zoo]] (1953{{ndash}}2014). Currently, the oldest hippo in captivity is believed to be [[Mae Mali]] at the [[Khao Kheow Open Zoo]] in Thailand, who will turn 60 in September 2025.

==Distribution and status==
[[File:Hippovictora.png|thumb|right|Ugandan tribespeople with hippo slain for food (early 20th century)]]
[[File:Incised hippopotamus ivory tusk, upper canine. Four holes around top. From Naqada Tomb 1419, Egypt. Naqada period. The Petrie Museum of Egyptian Archaeology, London.jpg|thumb|Incised hippopotamus ivory tusk (upper canine) with four holes around top (Naqada Tomb 1419, Egypt; Naqada period)]]
''Hippopotamus amphibius'' arrived in Europe around 560–460,000 years ago, during the Middle Pleistocene.<ref>{{Cite journal |last1=Mecozzi |first1=Beniamino |last2=Iannucci |first2=Alessio |last3=Mancini |first3=Marco |last4=Tentori |first4=Daniel |last5=Cavasinni |first5=Chiara |last6=Conti |first6=Jacopo |last7=Messina |first7=Mattia Yuri |last8=Sarra |first8=Alex |last9=Sardella |first9=Raffaele |date=2023-11-22 |editor-last=Carnevale |editor-first=Giorgio |title=Reinforcing the idea of an early dispersal of Hippopotamus amphibius in Europe: Restoration and multidisciplinary study of the skull from the Middle Pleistocene of Cava Montanari (Rome, central Italy) |journal=PLOS ONE |language=en |volume=18 |issue=11 |article-number=e0293405 |doi=10.1371/journal.pone.0293405 |issn=1932-6203 |pmc=10664965 |pmid=37992018 |doi-access=free|bibcode=2023PLoSO..1893405M }}</ref> The distribution of ''Hippopotamus amphibius'' in Europe during the Pleistocene was largely confined to Southern Europe, including the Iberian Peninsula,<ref name=":0">{{Cite journal |last1=Fidalgo |first1=Darío |last2=Madurell-Malapeira |first2=Joan |last3=Martino |first3=Roberta |last4=Pandolfi |first4=Luca |last5=Rosas |first5=Antonio |date=2024-01-10 |title=An Updated Review of The Quaternary Hippopotamus Fossil Records from the Iberian Peninsula |journal=Quaternary |language=en |volume=7 |issue=1 |page=4 |doi=10.3390/quat7010004 |doi-access=free |bibcode=2024Quat....7....4F |issn=2571-550X|hdl=10261/345195 |hdl-access=free }}</ref> Italy,<ref>{{Cite journal |last1=Briatico |first1=Giuseppe |last2=Gioia |first2=Patrizia |last3=Bocherens |first3=Hervé |date=10 December 2023 |title=Diet and habitat of the late Middle Pleistocene mammals from the Casal de' Pazzi site (Rome, Italy) using stable carbon and oxygen isotope ratios |url=https://linkinghub.elsevier.com/retrieve/pii/S1040618223003336 |journal=[[Quaternary International]] |language=en |volume=676 |pages=53–62 |doi=10.1016/j.quaint.2023.11.002 |bibcode=2023QuInt.676...53B |access-date=27 April 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref><ref name=":02">{{Cite journal |last1=Martino |first1=R. |last2=Pandolfi |first2=L. |date=2022-07-03 |title=The Quaternary Hippopotamus records from Italy |url=https://www.tandfonline.com/doi/full/10.1080/08912963.2021.1965138 |journal=Historical Biology |language=en |volume=34 |issue=7 |pages=1146–1156 |doi=10.1080/08912963.2021.1965138 |bibcode=2022HBio...34.1146M |issn=0891-2963 |s2cid=239713930|url-access=subscription }}</ref> and Greece,<ref name=":1">{{Citation |last=Athanassiou |first=Athanassios |title=The Fossil Record of Continental Hippopotamids (Mammalia: Artiodactyla: Hippopotamidae) in Greece |date=2022 |work=Fossil Vertebrates of Greece Vol. 2 |pages=281–299 |editor-last=Vlachos |editor-first=Evangelos |url=https://link.springer.com/10.1007/978-3-030-68442-6_9 |access-date=2024-01-26 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-68442-6_9 |isbn=978-3-030-68441-9|s2cid=239839913 |url-access=subscription }}</ref> but extended into northwestern Europe, including Great Britain (as far north as [[North Yorkshire]]), the Netherlands, and western Germany during [[interglacial]] periods, such as the [[Last Interglacial]] (130–115,000 years ago).<ref>{{Cite journal |last=Pushkina |first=Diana |date=July 2007 |title=The Pleistocene easternmost distribution in Eurasia of the species associated with the Eemian Palaeoloxodon antiquus assemblage |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2907.2007.00109.x |journal=Mammal Review |language=en |volume=37 |issue=3 |pages=224–245 |doi=10.1111/j.1365-2907.2007.00109.x |bibcode=2007MamRv..37..224P |issn=0305-1838 |url-access=subscription }}</ref><ref>{{Cite journal |last=van Kolfschoten |first=Th. |date=August 2000 |title=The Eemian mammal fauna of central Europe |url=https://www.cambridge.org/core/product/identifier/S0016774600021752/type/journal_article |journal=Netherlands Journal of Geosciences |language=en |volume=79 |issue=2–3 |pages=269–281 |doi=10.1017/S0016774600021752 |bibcode=2000NJGeo..79..269V |issn=0016-7746}}</ref><ref>{{Cite journal |last=Schreve |first=Danielle C. |date=January 2009 |title=A new record of Pleistocene hippopotamus from River Severn terrace deposits, Gloucester, UK—palaeoenvironmental setting and stratigraphical significance |url=https://linkinghub.elsevier.com/retrieve/pii/S0016787809000054 |journal=Proceedings of the Geologists' Association |language=en |volume=120 |issue=1 |pages=58–64 |bibcode=2009PrGA..120...58S |doi=10.1016/j.pgeola.2009.03.003|url-access=subscription }}</ref> Analysis of [[ancient DNA]] indicates that Late Pleistocene European hippopotamuses are closely related to and nested within the genetic diversity of living African hippopotamuses.<ref name=":2">{{Cite journal |last=Arnold |first=Patrick |last2=Döppes |first2=Doris |last3=Alberti |first3=Federica |last4=Füglistaler |first4=Andreas |last5=Lindauer |first5=Susanne |last6=Hoselmann |first6=Christian |last7=Friedrich |first7=Ronny |last8=Hajdas |first8=Irka |last9=Dickinson |first9=Marc |last10=Menger |first10=Frank |last11=Paijmans |first11=Johanna L.A. |last12=Dalén |first12=Love |last13=Wegmann |first13=Daniel |last14=Penkman |first14=Kirsty E.H. |last15=Barlow |first15=Axel |date=October 2025 |title=Ancient DNA and dating evidence for the dispersal of hippos into central Europe during the last glacial |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982225012059 |journal=Current Biology |language=en |doi=10.1016/j.cub.2025.09.035|doi-access=free }}</ref> The youngest records of the species in Europe are from the Late Pleistocene of Greece, and the [[Rhine Graben]] of southwest Germany, dating to around 40–30,000 years ago.<ref name=":1" /><ref name=":0" /><ref name=":2" />

Archaeological evidence exists of its presence in the [[Levant]], dating to less than 3,000 years ago.<ref>{{cite journal|last=Horwitz|first=Liora Kolska|author2= Tchernov, Eitan|title=Cultural and Environmental Implications of Hippopotamus Bone Remains in Archaeological Contexts in the Levant|journal=Bulletin of the American Schools of Oriental Research|year=1990|volume=280|issue=280|pages=67–76|doi=10.2307/1357310|jstor=1357310|s2cid=163871070}}</ref><ref>{{cite journal|last=Haas|first=Georg|title=On the Occurrence of Hippopotamus in the Iron Age of the Coastal Area of Israel|url=https://archive.org/details/sim_bulletin-of-the-american-schools-of-oriental-research_1953-12_132/page/30|journal=Bulletin of the American Schools of Oriental Research|year=1953|volume=132|issue=132|pages=30–34|doi=10.2307/1355798|jstor=1355798|s2cid=163758714}}</ref> The species was common in [[Egypt]]'s [[Nile]] region during [[Classical antiquity|antiquity]], but it has since been driven out. According to [[Pliny the Elder]], in his time, the best location in Egypt for capturing this animal was in the [[Sais, Egypt|Saite nome]];<ref name="Pliny">{{Cite book|title = Naturalis Historia|author = Pliny the Elder|author-link = Pliny the Elder|chapter = Chapter 15, Book VIII|language=en |isbn = 978-3-519-01652-6|title-link = Naturalis Historia|date = 1 January 1987| publisher=Vieweg+Teubner Verlag }} ([https://penelope.uchicago.edu/holland/pliny8.html English translation]; [https://penelope.uchicago.edu/Thayer/L/Roman/Texts/Pliny_the_Elder/8*.html Latin original])</ref> the animal could still be found along the [[Damietta]] branch of the Nile after the [[Arab conquest of Egypt|Arab conquest]] in 639. Reports of the slaughter of the last hippo in [[Natal Province]] were made at the end of the 19th century.<ref>{{Cite news|url=https://nla.gov.au/nla.news-article14137838|title=The Hippopotamus Going - Extinction of the huge species at hand|date=7 October 1898|work=The Sydney Morning Herald|access-date=14 July 2017}}</ref> Hippos are still found in the rivers and lakes of the northern [[Democratic Republic of the Congo]], [[Uganda]], [[Tanzania]], and [[Kenya]], north through to [[Ethiopia]], [[Somalia]], and [[Sudan]], west to [[The Gambia]], and south to [[South Africa]].<ref name="iucn" />

Genetic evidence suggests common hippos in Africa experienced a marked population expansion during or after the [[Pleistocene]], attributed to an increase in water bodies at the end of the era. These findings have important conservation implications, as hippo populations across the continent are currently threatened by loss of access to fresh water.<ref name="Okello"/> Hippos are also subject to unregulated hunting and [[poaching]]. The species is included in Appendix II of the [[Convention on International Trade in Endangered Species]] (CITES) meaning international export/import (including in parts and derivatives) requires CITES documentation to be obtained and presented to border authorities.<ref name=iucn/><ref name="Appendices {{!}} CITES">{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/index.php|access-date=2022-11-13|website=cites.org}}</ref>

As of 2017, the [[IUCN Red List]] drawn up by the [[International Union for Conservation of Nature]] (IUCN) lists the species as [[vulnerable species|vulnerable]], with a stable population estimated between 115,000 and 130,000 animals.<ref name=iucn/> The hippo population has declined most dramatically in the Democratic Republic of the Congo.<ref name="HippoHaven">{{cite news |url = http://www.smithsonianmagazine.com/issues/2006/january/hippos.php |title = Hippo Haven |work = [[Smithsonian Magazine]] |date = 1 January 2006 |access-date = 23 January 2007}}</ref> By 2005, the population in [[Virunga National Park]] had dropped to 800 or 900 from around 29,000 in the mid-1970s.<ref name="BBC"/> This decline is attributed to the disruptions caused by the [[Second Congo War]].<ref name="BBC">{{Cite news| title = DR Congo's hippos face extinction.|url = http://news.bbc.co.uk/2/hi/africa/4240420.stm|date = 13 September 2005|access-date = 14 November 2005|work = [[BBC]]}}</ref> The poachers are believed to be [[Mai-Mai]] rebels, underpaid Congolese soldiers, and local militia groups.<ref name="BBC"/><ref name=natgeo>{{cite web|author=Owen, James|date=24 October 2006|title=Hippos Butchered by the Hundreds in Congo Wildlife Park|publisher=National Geographic News|access-date=11 September 2013|url=http://news.nationalgeographic.com/news/2006/10/061024-hippo-congo.html| archive-url=https://web.archive.org/web/20140220005151/https://news.nationalgeographic.com/news/2006/10/061024-hippo-congo.html|archive-date=20 February 2014}}</ref> Reasons for poaching include the belief hippos are harmful to society, as well as financial gain.<ref name="Star"/> As of 2016, the Virunga hippo population appears to have increased again, possibly due to better protection from park rangers, who have worked with local fishermen.<ref>{{cite web|author1=Delaney, J. |author2=Sautner, S. |title=After a Long Demise Due to Poaching, Virunga's Hippos Climbing Back|publisher=Wildlife Conservation Society|access-date=25 November 2016|date=3 November 2016|url=https://newsroom.wcs.org/News-Releases/articleType/ArticleView/articleId/9373/After-a-Long-Demise-Due-to-Poaching,-Virunga%E2%80%99s-Hippos-Climbing-Back.aspx}}</ref> The sale of hippo meat is illegal, but black-market sales are difficult for Virunga National Park officers to track.<ref name=natgeo/><ref name="Star">{{Cite news |last=Sundaram |first=Anjan |title = Congo's Hippos Fast Disappearing |newspaper=[[Toronto Star]] |date=12 September 2005}}</ref> Hippo meat is highly valued in some areas of central Africa and the teeth may be used as a replacement for elephant ivory.<ref name="newscientist2003">{{cite journal | first= Fred | last = Pearce | title = Poaching causes hippo population crash | journal = New Scientist | year = 2003 | url = https://www.newscientist.com/article/dn4109-poaching-causes-hippo-population-crash.html#.U1vYUPldWz4 | access-date = 26 April 2014}}</ref>

A population of hippos [[Hippopotamuses in Colombia|exists in Colombia]], descended from captive individuals that escaped from [[Pablo Escobar]]'s estate after his death in 1993. Their numbers grew to 100 by the 2020s and ecologists believe the population should be eradicated, as they are breeding rapidly and are an increasing menace to humans and the environment. Attempts to control them include sterilisation and [[culling]].<ref>{{cite news |last1=Charles |first1=Matthew |title=Colombia's rapidly breeding 'cocaine hippos' must be stopped, scientists say |url=https://www.yahoo.com/news/colombias-rapidly-breeding-cocaine-hippos-153839192.html |access-date=January 18, 2021 |work=news.yahoo.com |publisher=The Telegraph |date=January 17, 2021}}</ref>

==Behaviour and ecology==
[[File:Hippo.ogv|thumb|right|Video of hippos in the wild]]
Hippos are [[semiaquatic]] and require enough water to immerse in, while being close to grass.<ref name=estes/> They mostly live in freshwater habitat, but can be found in [[estuaries]].<ref name=iucn/> They prefer relatively still waters with gently sloping shores, though male hippos may also be found in very small numbers in more [[Rapids|rapid]] waters with rocky slopes.<ref name=kingdon/>{{rp|264}} Like most herbivores, hippos will consume a variety of plants if presented with them in captivity, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants.<ref name="Grey"/> Hippos spend most of the day in water to stay cool and hydrated. Just before night begins, they leave the water to forage on land. A hippo will travel {{cvt|3|–|5|km}} per night, eating around {{cvt|40|kg}} of grass. By dawn, they are back in the water.<ref name=estes/>

Despite being semiaquatic, an adult hippo is not a particularly good swimmer, nor can it float. It rarely enters deep water; when it does, the animal moves by bouncing off the bottom. An adult hippo surfaces every four to six minutes, while young need to breathe every two to three minutes.<ref name="The Hippos"/>{{rp|3–4}} Hippos move on land by [[trot]]ting, and limb movements do not change between speeds. They can reach an airborne stage (a stage when all limb are off the ground) when they move fast enough. Hippos are reported to reach {{cvt|30|km/h}} but this has not been confirmed.<ref>{{cite journal|last1=Hutchinson|first1=J. R.|last2=Pringle|first2=E. V.|year=2024|title=Footfall patterns and stride parameters of Common hippopotamus (''Hippopotamus amphibius'') on land|journal=PeerJ|volume=12|article-number=e17675|doi=10.7717/peerj.17675|doi-access=free |pmid=38974416 |pmc=11227274}}</ref> They are incapable of jumping but can walk up steep banks.<ref name=estes/> The hippopotamus sleeps with both hemispheres of the brain resting, as in all land mammals, and usually sleeps on land or in water with the nostrils exposed. Despite this, it can sleep while submerged, intermittently surfacing to breathe seemingly without waking. They appear to transition between different phases of sleep more quickly than other mammals.<ref>{{cite journal|author1=Dell, Leigh-Anne|author2=Patzke, Nina|author3=Spocter, Muhammad A.|author4=Bertelsen, Mads F.|author5=Siegel, Jerome M.|author6=Manger, Paul R.|year=2016|title=Organization of the sleep-related neural systems in the brain of the river hippopotamus (''Hippopotamus amphibius''): A most unusual cetartiodactyl species|journal=Journal of Comparative Neurology|volume=524|issue=10|pages=2036–2058|doi=10.1002/cne.23930|pmid=26588600 |pmc=8716328 }}</ref>

Because of their size and their habit of taking the same paths to feed, hippos can have a significant impact on the land across which they walk, keeping the land clear of vegetation and depressing the ground. Over prolonged periods, hippos can divert the paths of swamps and channels.<ref name="Botswana">{{Cite journal|journal = African Journal of Ecology|volume = 36|issue = 1|pages = 44–56|year = 1998|author1=McCarthy, T. S. |author2=Ellery, W. N. |author3=Bloem, A |title = Some observations on the geomorphological impact of hippopotamus (''Hippopotamus amphibius'' L.) in the Okavango Delta, Botswana|doi = 10.1046/j.1365-2028.1998.89-89089.x| bibcode=1998AfJEc..36...44M }}</ref> By defecating in the water, the animals also appear to pass on microbes from their gut, affecting the [[biogeochemical cycle]].<ref>{{cite journal|author1=Dutton, C. L.|author2=Subalusky, A. L.|author3=Sanchez, A.|author4=Estrela, S.|author5=Lu, N.|author6=Hamilton, S. K.|author7=Njoroge, L.|author8=Rosi, E. J.|author9=Post, D. M.|year=2021|title=The meta-gut: community coalescence of animal gut and environmental microbiomes|journal=Scientific Reports|volume=11|issue=1|page=23117|doi=10.1038/s41598-021-02349-1|pmid=34848778 |pmc=8633035 |bibcode=2021NatSR..1123117D }}</ref> On occasion, hippos have been filmed eating [[carrion]], usually near the water. There are other reports of meat-eating and even [[cannibalism]] and [[predation]].<ref>{{Cite journal|title = Reports of carnivory by the common hippo ''Hippopotamus amphibius''|author = Dudley, J. P.|journal = South African Journal of Wildlife Research| date=January 1998 |volume = 28|issue = 2|pages = 58–59|url = https://journals.co.za/content/wild/28/2/EJC117046}}</ref> Hippos' stomach anatomy lacks adaptions to carnivory, and meat-eating is likely caused by lack of nutrients or represents an abnormal behaviour.<ref name="The Hippos"/>{{rp|82–84}}

===Social life===
[[File:Hippo pod edit.jpg|thumb|right|Hippopotamus pod]]
It is challenging to study the interaction of bulls and cows because hippos are not [[Sexual dimorphism|sexually dimorphic]], so cows and young bulls are almost indistinguishable in the field.<ref>{{Cite journal |journal=[[African Zoology]] |volume=37 |issue=2 |author1=Beckwitt, R. |author2=Shea, J. |author3=Osborne, D. |author4=Krueger, S. |author5=Barklow, W. |year=2002 |title=A PCR-based method for sex identification in ''Hippopotamus amphibius'' |pages=127–130 |url=http://www.framingham.edu/~rbeckwitt/hippo2002.pdf |archive-url=https://web.archive.org/web/20100617172906/http://www.framingham.edu/~rbeckwitt/hippo2002.pdf |archive-date=17 June 2010 |doi=10.1080/15627020.2002.11657167 |s2cid=88102117 }}</ref> Hippo pods fluctuate but can contain over 100 hippos. Although they lie close together, adults develop almost no social bonds. Males establish [[Territory (animal)|territories]] in water but not land, and these may range {{cvt|250|–|500|m}} in lakes and {{cvt|50|–|100|m}} in rivers. Territories are abandoned when the water dries up. The bull has breeding access to all the cows in his territory. Younger bachelors are allowed to stay as long as they defer to him. A younger male may challenge the old bull for control of the territory. Within the pods, the hippos tend to segregate by sex and status. Bachelor males lounge near other bachelors, females with other females, and the territorial male is on his own. When hippos emerge from the water to graze, they do so individually.<ref name="The Hippos"/>{{rp|4–5, 49–50}}

[[File:Hippo fight.jpg|thumb|left|Male hippos fighting]]
Hippos engage in "muck-spreading" which involves defecating while spinning their tails to distribute the faeces over a greater area. Muck-spreading occurs both on land and in water and its function is not well understood. It is unlikely to serve a territorial function, as the animals only establish territories in the water. They may be used as trails between the water and grazing areas.<ref name="The Hippos"/>{{rp|5, 51–52}} "Yawning" serves as a threat display.<ref name=estes/> When fighting, bulls use their incisors to block each other's attacks and their large canines as offensive weapons.<ref name=kingdon/>{{rp|259–260}} When hippos become over-populated or a habitat shrinks, bulls sometimes attempt [[Infanticide (zoology)|infanticide]], but this behaviour is not common under normal conditions.<ref name="Infanticide"/>

The most common hippo vocalisation is the "wheeze honk", which can travel over long distances in air.<ref name=wheeze-honk/> This call starts as a high-pitched squeal followed by a deeper, resonant call.<ref name="The Hippos"/>{{rp|5}} The animals can recognise the calls of other individuals. Hippos are more likely to react to the wheeze honks of strangers than to those they are more familiar with ([[dear enemy effect]]).<ref name=wheeze-honk>{{cite journal|last1=Thévenet|first1=J.|last2=Grimault|first2=N.|last3=Fonseca|first3=P.|last4=Mathevon|first4=N.|year=2022|title=Voice-mediated interactions in a megaherbivore|journal=Current Biology|volume=32|issue=2|pages=R70–R71|doi=10.1016/j.cub.2021.12.017|pmid=35077689 |bibcode=2022CBio...32..R70T |s2cid=246242737 |url=https://hal.archives-ouvertes.fr/hal-03543609/file/Pre-Print-CURRENT-BIOLOGY.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://hal.archives-ouvertes.fr/hal-03543609/file/Pre-Print-CURRENT-BIOLOGY.pdf |archive-date=2022-10-09 |url-status=live }}</ref> When threatened or alarmed, they produce exhalations,<ref name=estes/> and fighting bulls will bellow loudly.<ref name="The Hippos"/>{{rp|5}} Hippos are recorded to produce clicks underwater which may have [[Animal echolocation|echolocative]] properties.<ref>{{cite journal|last1=Maust-Mohl|first1=M|last2=Soltis|first2=J|last3= Reiss|first3=D|year=2018|title=Underwater click train production by the hippopotamus (''Hippopotamus amphibius'') suggests an echo-ranging function|journal=Behaviour|volume=155|issue=2–3|pages=231–251|doi=10.1163/1568539X-00003484|jstor=26488527}}</ref> They have the unique ability to hold their heads partially above the water and send out a cry that travels through both water and air; individuals respond both above and below water.<ref>{{Cite journal|title = Low-frequency sounds and amphibious communication in ''Hippopotamus amphibious''|url = http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JASMAN000115000005002555000001&idtype=cvips&gifs=yes|journal = The Journal of the Acoustical Society of America|author = Barklow, William E.|year = 2004|volume = 115|issue = 5|page = 2555|doi=10.1121/1.4783854|bibcode = 2004ASAJ..115.2555B|url-access = subscription}}</ref>

===Reproduction===
[[File:Mother and Young Hippo, Uganda (15397037561).jpg|thumb|right|Cow and calf]]
Cows reach sexual maturity at five to six years of age and have a [[pregnancy (mammals)|gestation period]] of eight months.<ref>{{cite journal|last1=Brown|first1=C. Emerson|title=Rearing Hippopotamuses in Captivity|url=https://archive.org/details/sim_journal-of-mammalogy_1924-11_5_4/page/n33|journal=Journal of Mammalogy|date=November 1924|volume=5|issue=4|pages=243–246|doi=10.2307/1373731|jstor=1373731}}</ref> A study of [[endocrine system]]s revealed cows may begin puberty at as early as three or four years.<ref name="Endocrine">{{Cite journal|title = Endocrine patterns associated with reproduction in the Nile hippopotamus (''Hippopotamus amphibius'') as assessed by fecal progestagen analysis|journal=General and Comparative Endocrinology|volume=128|issue=1|year=2002|pages=74–81|author1=Graham, L. H.|author2= Reid, K. |author3=Webster, T. |author4=Richards, M. |author5=Joseph, S. |doi=10.1016/S0016-6480(02)00066-7|pmid = 12270790}}</ref> Bulls reach maturity at around 7.5 years. Both conceptions and births are highest during the [[wet season]]. Male hippos always have mobile [[spermatozoa]] and can breed year-round.<ref name="The Hippos"/>{{rp|59–61, 66}} After becoming pregnant, a female hippo will typically not begin ovulation again for 17 months.<ref name="Endocrine"/> Hippos mate in the water, with the cow remaining under the surface,<ref name="The Hippos"/>{{rp|63}} her head emerging periodically to draw breath. Cows  give birth in seclusion and return within 10 to 14 days. Calves are born on land or shallow water<ref name=estes/> weighing on average {{cvt|50|kg}} and at an average length of around {{cvt|127|cm}}. The female lies on her side when nursing, which can occur underwater or on land. The young are carried on their mothers' backs in deep water.<ref name="The Hippos"/>{{rp|4, 64}}

Mother hippos are very protective of their young, not allowing others to get too close.<ref name=estes/> One cow was recorded protecting a calf's carcass after it had died.<ref>{{cite journal|author1=Inman, V. L.|author2=Leggett, K. E. A.|year=2020|title=Observations on the response of a pod of hippos to a dead juvenile hippo (''Hippopotamus amphibius'', Linnaeus 1758)|journal=African Journal of Ecology|volume=58|issue=1|pages=123–125|doi=10.1111/aje.12644|bibcode=2020AfJEc..58..123I |s2cid=191169281 }}</ref> Calves may be temporarily kept in [[Crèche (zoology)|nurseries]], guarded by one or more adults, and will play amongst themselves.<ref name=estes/> Like many other large mammals, hippos are described as [[k-selection|K-strategists]], in this case typically producing just one large, well-developed infant every couple of years (rather than many small, poorly developed young several times per year, as is common among small mammals such as rodents).<ref name="Endocrine"/><ref name="Infanticide">{{Cite journal|doi = 10.1080/08927014.1998.9522857|title = Infanticide in the hippopotamus: evidence for polygynous ungulates|author = Lewison, R.|journal = Ethology, Ecology & Evolution|volume = 10|issue = 3|pages = 277–286|year = 1998| bibcode=1998EtEcE..10..277L |url = http://www.fupress.net/index.php/eee/article/viewFile/805/751|access-date = 11 July 2010|archive-date = 6 March 2011|archive-url = https://web.archive.org/web/20110306033554/http://www.fupress.net/index.php/eee/article/viewFile/805/751|url-access = subscription}}</ref> Calves no longer need to suckle when they are a year old.<ref name="The Hippos"/>{{rp|64}}

===Interspecies interactions===
[[File:Kruger-Park-Hippo-And-Crocodile.jpg|thumb|right|A hippopotamus and Nile crocodile side by side in Kruger National Park]]
Hippos coexist alongside a variety of large predators in their habitats. [[Nile crocodile]]s, [[lion]]s, and [[spotted hyena]]s are known to prey on young hippos.<ref name=estes/> Beyond these, adult hippos are not usually preyed upon by other animals due to their aggression and size. Cases where large lion prides have successfully preyed on adult hippos have been reported, but it is generally rare.<ref>{{cite book|last = Hunter|first = Luke|title = Carnivores of the World|publisher = [[Princeton University Press]]|year = 2011|isbn = 978-0-691-15228-8}}</ref> Lions occasionally prey on adults at [[Gorongosa National Park]] and calves are sometimes taken at Virunga.<ref>{{Cite book | last= Schaller |first= George B. |year= 1972 |title= The Serengeti lion: A study of predator–prey relations|publisher= University of Chicago Press|pages=208–209|isbn = 978-0-226-73639-6 }}</ref> [[Crocodile]]s are frequent targets of hippo aggression, probably because they often inhabit the same [[riparian]] habitats; crocodiles may be either aggressively displaced or killed by hippos,<ref>{{cite book|last1 = Ross|first1 = Charles A.|last2 = Garnett|first2 = Stephen|title = Crocodiles and Alligators|publisher = Checkmark Books|year = 1989|isbn = 978-0-8160-2174-1}}</ref> although they will avoid crocodiles larger than {{cvt|3.5|m}}.<ref name="Kofron 1993">{{cite journal |last=Kofron |first=Christopher |title= Behavior of Nile Crocodiles in a Seasonal River in Zimbabwe |journal= American Society of Ichthyologists and Herpetologists |date=May 3, 1993 |volume=1993 |issue=2 |pages=463–469 |doi=10.2307/1447146 |jstor= 1447146}}</ref> In turn, very large Nile crocodiles have been observed preying occasionally on calves, "half-grown" hippos, and possibly also adult female hippos. Groups of crocodiles have also been observed finishing off still-living male hippos that were previously injured in mating battles with other males.<ref name="Cott">{{cite journal|author=Cott, H. B. |title=Scientific results of an inquiry into the ecology and economic status of the Nile crocodile (''Crocodilus niloticus'') in Uganda and Northern Rhodesia|journal=The Transactions of the Zoological Society of London|volume=29|issue=4|pages=211–356|doi=10.1111/j.1096-3642.1961.tb00220.x|year=2010}}</ref><ref name="Guggisberg">{{cite book | author = Guggisberg, C. A. W. | title = Crocodiles: Their Natural History, Folklore, and Conservation| year = 1972 | isbn = 978-0-7153-5272-4 | page = 195| publisher = David & Charles}}</ref>

Hippos occasionally visit [[cleaning stations]] in order to be cleaned of parasites by certain species of fishes. They signal their readiness for this service by opening their mouths wide. This is an example of [[Mutualism (biology)|mutualism]], in which the hippo benefits from the cleaning while the fish receive food.<ref>{{cite book|author1 =Balcombe, Jonathan|year=2006|title=Pleasurable Kingdom: Animals and the Nature of Feeling Good|url =https://archive.org/details/pleasurablekingd00balc_653|url-access =limited|publisher=Palgrave Macmillan|pages=[https://archive.org/details/pleasurablekingd00balc_653/page/n140 132]–133|isbn=978-1-4039-8602-3}}</ref> Hippo defecation creates [[allochthonous]] deposits of organic matter along the river beds. These deposits have an unclear ecological function.<ref name="Grey">{{Cite journal|title = Using Stable Isotope Analyses To Identify Allochthonous Inputs to Lake Naivasha Mediated Via the Hippopotamus Gut| author = Grey, J.| author2 = Harper, D. M.|journal = Isotopes in Environmental Health Studies|volume = 38|issue = 4|year = 2002|pages = 245–250|doi = 10.1080/10256010208033269| pmid = 12725427| bibcode = 2002IEHS...38..245G| s2cid = 216152807}}</ref> A 2015 study concluded hippo dung provides nutrients from terrestrial material for fish and aquatic invertebrates,<ref>{{cite journal|author=McCauley, D. J.|year=2015|title=Carbon stable isotopes suggest that hippopotamus-vectored nutrients subsidize aquatic consumers in an East African river|journal=Ecosphere|volume=6|issue=4|pages=1–11|doi=10.1890/ES14-00514.1|display-authors=etal|doi-access=free}}</ref> while a 2018 study found that their dung can be toxic to aquatic life in large quantities, due to absorption of dissolved oxygen in water bodies.<ref>{{cite journal|author1=Dutton, C. L. |author2=Subalusky, A. L. |author3=Hamilton, S. K. |author4=Rosi, E. J. |author5=Post, D. M. |year=2018|title=Organic matter loading by hippopotami causes subsidy overload resulting in downstream hypoxia and fish kills|journal=Nature Communications|volume=9|issue=1951|page=1951 |doi=10.1038/s41467-018-04391-6|pmid=29769538 |pmc=5956076|bibcode=2018NatCo...9.1951D }}</ref><ref>{{cite web |url=https://www.theatlantic.com/science/archive/2018/05/hippos-poop-so-much-that-sometimes-all-the-fish-die/560486/ |title=Hippos Poop So Much That Sometimes All the Fish Die |last=Yong |first=Ed |work=The Atlantic |date=16 May 2018 |access-date=23 June 2021 }}</ref>

The parasitic [[monogenea]]n [[flatworm]]'' Oculotrema hippopotami'' infests hippopotamus eyes, mainly the nictitating membrane. It is the only monogenean species (which normally live on fish) documented to live on a mammal.<ref>{{cite journal|author1=Rubtsova, N. Y.|author2=Heckmann, R. A.|author3=Smit, W. J.|author4=Luus-Powell, W. J.|author5=Halajian, A.|author6=Roux, F.|year=2018|title=Morphological studies of developmental stages of ''Oculotrema hippopotami'' (Monogenea: Polystomatidae) infecting the eye of ''Hippopotamus amphibius'' (Mammalia: Hippopotamidae) ssing SEM and EDXA with notes on histopathology|journal=The Korean Journal of Parasitology|volume=56|issue=5|pages=463–475|doi=10.3347/kjp.2018.56.5.463|pmid=30419732 |pmc=6243182 |s2cid=53289954 }}</ref>

==Relationship with humans==
[[File:Standing Hippopotamus MET DP248993.jpg|thumb|Hippopotamus ([[William the Faience Hippopotamus|"William"]]), [[Middle Kingdom of Egypt]], {{circa}} 1961–1878 BC]]
Cut marks on bones of ''H. amphibius'' found at [[Bolomor Cave]], a site in Spain preserving fossils dating from 230,000 to 120,000 years ago, provides evidence for [[Neanderthal]] butchery of hippopotamuses.<ref>{{Cite journal |last=Pawłowska |first=K. |date=2017 |title=Large mammals affected by hominins: Paleogeography of butchering for the European Early and Middle Pleistocene |journal=[[Quaternary International]] |volume=438 |pages=104–115 |doi=10.1016/j.quaint.2017.03.043|bibcode=2017QuInt.438..104P }}</ref><ref>{{Cite journal |last1=Blasco |first1=Ruth |last2=Rosell |first2=Jordi |last3=Fernández Peris |first3=Josep |last4=Arsuaga |first4=Juan Luis |last5=Bermúdez de Castro |first5=José María |last6=Carbonell |first6=Eudald |date=June 2013 |title=Environmental availability, behavioural diversity and diet: a zooarchaeological approach from the TD10-1 sublevel of Gran Dolina (Sierra de Atapuerca, Burgos, Spain) and Bolomor Cave (Valencia, Spain) |url=https://linkinghub.elsevier.com/retrieve/pii/S0277379113001133 |journal=Quaternary Science Reviews |language=en |volume=70 |pages=124–144 |doi=10.1016/j.quascirev.2013.03.008|bibcode=2013QSRv...70..124B |url-access=subscription }}</ref> The earliest evidence of modern human interaction with hippos comes from butchery cut marks on hippo bones found at the [[Bouri Formation]] and dated to around 160,000 years ago.<ref name=Clark>{{cite journal |doi=10.1038/nature01670 |last1=Clark |first1=J. D. |last2=Beyene |first2=Y. |last3=WoldeGabriel |first3=G. |last4=Hart |first4=W. K. |last5=Renne |first5=P. R. |last6=Gilbert |first6=H. |last7=Defleur |first7=A. |last8=Suwa |first8=G. |last9=Katoh |first9=S. |last10=Ludwig |first10=K. R. |last11=Boisserie |first11=J.-R. |last12=Asfaw |first12=Berhane |last13=White |first13=T. D. |year=2003 |title=Stratigraphic, chronological and behavioural contexts of Pleistocene Homo sapiens from Middle Awash, Ethiopia |journal=Nature |volume=423 |issue=6941 |pages=747–752 |pmid=12802333 |bibcode=2003Natur.423..747C |s2cid=4312418}}</ref> 4,000–5,000 year art showing hippos being hunted have been found in the [[Tassili n'Ajjer|Tassili n'Ajjer Mountains]] of the central [[Sahara]] near [[Djanet]].<ref name="The Hippos"/>{{rp|1}} The [[ancient Egypt]]ians recognised the hippo as ferocious, and representations on the tombs of nobles show humans hunting them.<ref>{{cite book |author=Atiya, F. |year=2008 |title=Ancient Egypt |publisher=The American University in Cairo Press |page=164|isbn=978-977-17-4439-9}}</ref>

The hippo was also known to the [[Ancient Greece|Greeks]] and [[Ancient Rome|Romans]]. The Greek historian [[Herodotus]] described the hippo in ''[[Histories (Herodotus)|The Histories]]'' (written ''[[Wiktionary:circa|circa]]'' 440 BC) and the Roman naturalist [[Pliny the Elder]] wrote about the hippo in his encyclopedia ''[[Naturalis Historia]]'' (written ''circa'' 77 AD).<ref name="Pliny"/><ref>{{Cite book |title= The Histories |author=Herodotus|author-link=Herodotus |chapter=Chapter 71, Book II |isbn = 978-0-19-521974-6|title-link = Histories (Herodotus)|date =2003| publisher=Oxford University Press, Incorporated |chapter-url=https://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus%3Aabo%3Atlg%2C0016%2C001&query=2%3A71%3A1}}</ref> The [[Yoruba people]] called the hippo ''erinmi'', which means "elephant of the water".<ref>{{cite book |author=Drewal, M. T. |year=1992|title=Yoruba Ritual: Performers, Play, Agency |publisher=Indiana University Press|page=74|isbn=978-0-253-11273-6}}</ref> Some individual hippos have achieved international fame. [[Huberta (hippopotamus)|Huberta]] became a celebrity during the Great Depression for trekking a great distance across [[South Africa]].<ref>{{Cite book |title=Huberta Goes South, a Record of the Lone Trek of the Celebrated Zululand Hippopotamus |author=Chilvers, H. A. |year=1931 |publisher=Gordon & Gotch|location=London}}</ref><ref name=reaktion/>{{rp|111–112}}

===Attacks on humans===
The hippo is considered to be extremely aggressive and has frequently been reported charging and attacking boats.<ref>{{cite web |url=http://www.petethomasoutdoors.com/2015/01/massive-hippo-charges-safari-boat-in-malawi-africa-.html|title=Massive hippo charges safari boat in Malawi, Africa|last=Thomas|first=Pete|publisher=Pete Thomas Outdoor|date=14 January 2015}}</ref> Hippos can easily capsize small boats and injure or kill passengers. In one 2014 case in [[Niger]], a boat was capsized by a hippo and 13 people were killed.<ref>{{cite news|url=https://www.abc.net.au/news/2014-11-20/hippopotamus-attack-kills-13-in-boat-in-niger/5904646|title=Hippopotamus attack kills 13 people, including 12 children, in boat near Niger's capital Niamey|publisher=Australian Broadcasting Corporation|date=20 November 2014}}</ref> Hippos will often raid farm crops if the opportunity arises, and humans may come into conflict with them on these occasions. These encounters can be fatal to either humans or hippos.<ref>{{Cite journal |author=Kendall, C. J. |year=2011 |title=The spatial and agricultural basis of crop raiding by the Vulnerable common hippopotamus ''Hippopotamus amphibius'' around Ruaha National Park, Tanzania |journal=Oryx |volume=45 |issue=1 |pages=28–34 |doi=10.1017/S0030605310000359 |doi-access=free}}</ref>

According to the [[Ptolemaic kingdom|Ptolemaic]] historian [[Manetho]], the [[pharaoh]] [[Menes]] was carried off and then killed by a hippopotamus.<ref>{{Cite book |last=Elder |first=E. |year=1849 |title=Dictionary of Greek and Roman biography and mythology |editor-last=Smith |editor-first=W. |volume=2 |place=Boston |publisher=[[Little, Brown and Company|Charles C. Little & James Brown]] |url=https://books.google.com/books?id=HP4rAAAAYAAJ}}</ref>

===In zoos===
[[File:Obaysch 1852.jpg|thumb|right|[[Obaysch]] lounging at the [[London Zoo]] in 1852]]
Hippos have long been popular zoo animals. The first record of hippos taken into captivity for display is dated to 3500 BC in Hierakonpolis, Egypt.<ref>{{cite journal |author=Rose, M. |year=2010|title=World's first Zoo-Hierakonpolis, Egypt. |journal=Archaeology |volume=63 |issue=1 |pages=25–32}}</ref> The first zoo hippo in modern history was [[Obaysch]], who arrived at the [[London Zoo]] on 25 May 1850, where he attracted up to 10,000 visitors a day and inspired a popular song, the "Hippopotamus Polka".<ref name=Mania>{{Cite journal |author=Root, N. J. |title=Victorian England's Hippomania |journal=[[Natural History (magazine)|Natural History]] |volume=103 |year=1993 |pages=34–39}}</ref>

Hippos generally breed well in captivity; birth rates are lower than in the wild, but this can be attributed to zoos' desire to limit births, since hippos are relatively expensive to maintain.<ref name=Mania/><ref>{{cite journal|last1=Snyder|first1=K. D. |title=The common Hippopotamus in the wild and in captivity: Conservation for less charismatic species |journal=Journal of International Wildlife Law & Policy |date=2015 |volume=18 |issue=4 |pages=337–354 |doi=10.1080/13880292.2015.1096162 |s2cid=86295612}}</ref> Starting in 2015, the [[Cincinnati Zoo]] built a US$73 million exhibit to house three adult hippos, featuring a {{cvt|250,000|L}} tank. Modern hippo enclosures also have a complex filtration system for waste, an underwater viewing area for the visitors, and glass that may be up to {{cvt|9|cm}} thick and capable of holding water under pressures of {{cvt|31|kPa}}.<ref name=reaktion/>{{rp|158–159}}

===Cultural significance===
{{See also|List of fictional pachyderms}}
[[File:Kalabari masks BM.jpg|thumb|left|upright|Ijaw hippopotamus masks]]
In [[Egyptian mythology]], the god [[Set (deity)|Set]] takes the form of a red hippopotamus and fights [[Horus]] for control of the land, but is defeated. The goddess [[Tawaret]] is depicted as a pregnant woman with a hippo head, representing fierce maternal love.<ref>{{cite book |last=Sax |first=B. |year=2001 |title=The Mythical Zoo: An Encyclopedia of Animals in World Myth, Legend, and Literature |publisher=ABC-CLIO |page=156 |isbn=978-1-57607-612-5}}</ref> The [[Ijaw people]] of the [[Niger Delta]] wore masks of aquatic animals like the hippo when practising their [[water spirit]] cults,<ref>{{cite book |author=Segy, L. |year=1976|title=Masks of Black Africa |publisher=Courier Corporation |page=128 |isbn=978-0-486-23181-5}}</ref> and hippo ivory was used in the [[divination]] rituals of the Yoruba.<ref>{{cite book |author=Blier, S. P. |year=2015|title=Art and Risk in Ancient Yoruba: Ife History, Power, and Identity, ca. 1300|publisher=Cambridge University Press |page=328 |isbn=978-1-107-02166-2}}</ref> Hippo masks were also used in [[Nyau]] funerary rituals of the [[Chewa people|Chewa]] of Southern Africa.<ref name=reaktion/>{{rp|120}} According to [[Robert Baden-Powell, 1st Baron Baden-Powell|Robert Baden-Powell]], [[Zulu people|Zulu]] warriors referred to hippos in war chants.<ref>{{cite web|last=Orans |first=L. P. |title=Scouting in South Africa 1884–1890 |url=http://www.pinetreeweb.com/bp-dinizulu.htm |publisher=Pinetreeweb |date=1997 |archive-url=https://web.archive.org/web/20140728235654/http://pinetreeweb.com/bp-dinizulu.htm |archive-date=28 July 2014 |access-date=29 March 2011}}</ref> The [[Behemoth]] from the [[Book of Job]], 40:15–24 is thought to be based on the hippo.<ref>{{cite book |editor1=Metzger, B. M. |editor2=Coogan, M. D. |title=The Oxford Companion to the Bible |publisher=Oxford University Press |year=1993 |location=Oxford, UK |page=76 |isbn=978-0-19-504645-8 |url=https://archive.org/details/isbn_9780195046458/page/76}}</ref>

Hippos have been the subjects of various [[African folklore|African folktales]]. According to a [[San people|San]] story, when the [[Creator deity|Creator]] assigned each animal its place in nature, the hippos wanted to live in the water, but were refused out of fear they might eat all the fish. After begging and pleading, the hippos were finally allowed to live in the water on the condition they would eat grass instead of fish, and fling their dung so it can be inspected for fish bones. In a Ndebele tale, the hippo originally had long, beautiful hair, but it was set on fire by a jealous hare and the hippo had to jump into a nearby pool. The hippo lost most of his hair and was too embarrassed to leave the water.<ref name=folktale>{{cite book |author1=Greaves, N. |author2=Clement, R. |year=2000|title=When Hippo Was Hairy: And Other Tales from Africa |publisher=Struik|pages=67–71|isbn=978-1-86872-456-7}}</ref>

[[File:Hippopotamus-polka-early1850s.jpg|thumb|upright|right|The "Hippopotamus Polka"]]
Hippopotamuses were rarely depicted in European art during the [[Renaissance]] and [[Baroque]] periods, due to less access to specimens by Europeans. One notable exception is [[Peter Paul Rubens]]' ''[[The Hippopotamus and Crocodile Hunt]]'' (1615–1616).<ref name=reaktion/>{{rp|122–123}} Ever since [[Obaysch]] inspired the "Hippopotamus Polka", hippos have been popular animals in [[Western culture]] for their rotund appearance, which many consider comical.<ref name="Mania"/> The [[The Walt Disney Company|Disney]] film ''[[Fantasia (1940 film)|Fantasia]]'' featured a ballerina hippo dancing to the opera ''[[La Gioconda (opera)|La Gioconda]]''. The film ''[[Hugo the Hippo]]'' is set in Tanzania and involves the title character trying to escape being slaughtered with the help of local children. The ''[[Madagascar (franchise)|Madagascar]]'' films feature a hippo named [[List of Madagascar (franchise) characters#Gloria|Gloria]].<ref name=reaktion>{{Cite book |last1=Willams|first1=E.|year=2017 |title=Hippopotamus |publisher=[[Reaktion Books]] |isbn=978-1-78023-779-4 |url=https://books.google.com/books?id=sN5BDwAAQBAJ&pg=PA129}}</ref>{{rp|128–129}} Hippos even inspired a popular board game, [[Hungry Hungry Hippos]].<ref>{{cite book |last1=Robinson|first1=P. T.|last2=Flacke|first2=G. L. |last3=Hentschel |first3=K. M. |year=2017|title=The Pygmy Hippo Story: West Africa's Enigma of the Rainforest |publisher=Oxford University Press |isbn=978-0-19-061185-9}}</ref>

Among the most famous poems about the hippo is "The Hippopotamus" by [[T. S. Eliot]], where he uses a hippo to represent the Catholic Church. Hippos are mentioned in the novelty Christmas song "[[I Want a Hippopotamus for Christmas]]" that became a hit for child star [[Gayla Peevey]] in 1953. They also featured in the popular "The Hippopotamous Song" by [[Flanders and Swann]].<ref name=reaktion/>{{rp|128, 136}}

==See also==
{{Portal|Mammals}}
* [[American Hippo bill]] - 1910 bill that proposed the introduction of hippos into Louisiana 
* [[List of individual hippos]]

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Hippopotamus amphibius}}
{{Wikiquote}}
*{{cite web |url=http://awf.org/content/wildlife/detail/hippopotamus |archive-url=https://web.archive.org/web/20101119172410/http://awf.org/content/wildlife/detail/hippopotamus |archive-date=19 November 2010 |title=Hippos: Wildlife summary |publisher=[[African Wildlife Foundation]]}}
*{{cite web |url=http://www.ml.duke.edu/projects/hippos/ |title=Hippo Specialist Group of the World Conservation Union |publisher=[[International Union for Conservation of Nature]] |archive-url=https://web.archive.org/web/20141122203937/http://www.ml.duke.edu/projects/hippos/ |archive-date=22 November 2014 |access-date=4 November 2008 }} 
*{{cite web |url= http://www.history.com/news/history-lists/11-things-you-may-not-know-about-ancient-egypt|title= 11 Things You May Not Know About Ancient Egypt: King Tut may have been killed by a hippopotamus|date= 12 November 2012|publisher= [[History (U.S. TV channel)|History]]|archive-url= https://web.archive.org/web/20141217213422/http://www.history.com/news/history-lists/11-things-you-may-not-know-about-ancient-egypt|archive-date= 17 December 2014|url-status= live}}

{{Artiodactyla|C.}}
{{Taxonbar|from=Q34505}}
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[[Category:Hippopotamuses| ]]
[[Category:Mammals of Africa]]
[[Category:Fauna of Sub-Saharan Africa]]
[[Category:Herbivorous mammals]]
[[Category:Vulnerable animals]]
[[Category:Vulnerable biota of Africa]]
[[Category:Mammals described in 1758]]
[[Category:Articles containing video clips]]
[[Category:Animal taxa named by Carl Linnaeus]]
[[Category:Semiaquatic mammals]]