Red-breasted merganser

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The red-breasted merganser (Mergus serrator) is a duck species that is native to much of the temperate to subarctic Northern Hemisphere. The red breast that gives the species its common name is only displayed by males in breeding plumage. Individuals fly rapidly, and feed by diving from the surface to pursue aquatic animals underwater, using serrated bills to capture slippery fish. They migrate each year from breeding sites on lakes and rivers to their mostly coastal wintering areas, making them the most frequent species in the genus Mergus to frequent saltwater regularly. The worldwide population of this species is stable, though it is threatened in some areas by habitat loss and other factors.

Taxonomy

The red-breasted merganser was formally described in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae under the current binomial name Mergus serrator.<ref>Template:Cite book</ref><ref>Template:Cite book</ref> The species is monotypic; no subspecies are recognised.<ref name=ioc>Template:Cite web</ref> Birds breeding in Greenland were sometimes distinguised as a subspecies M. s. schioleri in the past on the basis of averaging very marginally larger, but this is no longer accepted as distinct.<ref name="BWP">Template:Cite book</ref><ref name="Madge">Template:Cite book</ref><ref name=ioc/>

Etymology

The genus name Mergus is a Latin word used by Pliny and other Roman authors to refer to an unspecified water bird. The specific epithet serrator is Latin for sawyer and is ultimately from serra, meaning saw. It refers to the saw-like projections on the bird's bill, which enable it to hold on to slippery fish, its most frequent prey.<ref name= job90>Template:Cite book</ref>

Description

The adult red-breasted merganser is Template:Convert long, has a wingspan of Template:Convert. Males average slightly larger, weighing Template:Convert, compared to female weight of Template:Convert.<ref name="BWP"/><ref>Template:Cite web</ref>

It has a spiky crest and long thin red bill with serrated edges. The male has a dark head with a green sheen, a white neck with a rusty breast, a black back, and white underparts. Adult females have a rusty head and a greyish-brown body. Juveniles look similar to females, but have a shorter crest, and marginally smaller white wing patches.<ref name="Madge"/>

The range of the red-breasted merganser broadly overlaps with that of the similar and closely related common merganser. The two species can therefore occur in the same place at the same time, though the species often choose different habitats (red-breasted prefers saltwater, common prefers freshwater, but overlap is frequent).<ref name="Madge"/> Breeding male plumages are fairly distinctive, but other plumages such as those born by females, immatures, and non-breeding males can make the two species hard to distinguish. Female common merganser has more contrast between the darker head and lighter breast, and has a light chin patch not seen on the red-breasted.<ref name="VsCommon">Template:Cite web</ref>

Voice

During courtship, the female gives a rasping prrak prrak, while the male gives a catlike meow. In flight, the female makes a harsh gruk. At other times this species is largely silent.<ref name="Sounds">Template:Cite web</ref>

Behaviour

Display

Male red-breasted mergansers show a highly stereotypic metronomic courtship display, in which they stretch, bend and contract their necks, often in synchrony by several males together, showing their crests alternately fanned and staight; females watch from nearby to select their preferred mate, and often chase or even attack the males. Display, which takes place while swimming, starts in mid November, and continues until June or rarely July.<ref name="BWP"/>

Food and feeding

Red-breasted mergansers dive and swim underwater. They mainly eat small fish, but also consume aquatic insects, worms, crustaceans, and amphibians.<ref name="AnimalDiversity" />

Breeding

Its breeding habitat is freshwater lakes and rivers across northern North America, Greenland, Europe, and the Palearctic. It nests in sheltered locations on the ground near water, often, but far from always, close to estuaries or sea coasts.<ref name="Madge"/>

Migration

It is mostly migratory and northern breeders winter in coastal waters further south. Populations in parts of northwestern Europe with oceanic climates (Iceland, Ireland, Britain, Norway, and Baltic Sea islands) are largely resident or disperse only short distances.<ref name="BWP"/> Outside of the breeding season, it forms flocks, which tend to be smaller during spring migration than they are in autumn migration and in winter. <ref name="BirdLife" />

Conservation

The red-breasted merganser is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies. The species is also considered a game bird under the Migratory Bird Treaty between the United States and Canada.<ref name="FWSSpeciesList">Template:Cite web</ref> This means that the species gets some protection, though hunting it is legal in North America in certain seasons and places determined by local hunting regulations. However, few hunters are interested in the species and relatively few birds are harvested.<ref name=AnimalDiversity>Template:Cite web</ref>

The species is widespread and common enough to be given conservation status of least concern by the IUCN, though populations in some areas may be declining. Threats include habitat loss through wetland destruction, exposure to toxins such as pesticides and lead, and becoming bycatch of commercial fishing operations.<ref name="AnimalDiversity" /> Anglers and fish farmers have also persecuted the species, which they regard as a competitor, though the impact of this on the species' population overall is not known;<ref name="BirdLife">Template:Cite web</ref> illegal persecution by fisheries interests is however significant in Britain, particularly Scotland.<ref>Template:Cite book</ref>