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Mergus merganser
Mergus merganser merganser, male in Sandwell, England
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Anseriformes
Family: Anatidae
Genus: Mergus
Species: M. merganser
Binomial name
Mergus merganser
Linnaeus, 1758
Range
Synonyms

Merganser americanus Cassin, 1852

The Common Merganser (North American) or Goosander (Eurasian) Mergus merganser is a large duck, of rivers and lakes of forested areas of Europe, northern and central Asia, and North America. It eats fish and nests in holes in trees.

It is 58-72 cm (29.7 in) long with a 78-97 cm (39.8 in) wingspan, and a weight of 0.9–2.1 kg; males average slightly larger than females but with some overlap. Like other species in the genus Mergus, it has a crest of longer head feathers, but these usually lie smoothly rounded behind the head, not normally forming an erect crest. Adult males in breeding plumage are easily distinguished, the body white with a variable salmon-pink tinge, the head black with an iridescent green gloss, the rump and tail grey, and the wings largely white on the inner half, black on the outer half. Females, and males in 'eclipse' (non-breeding plumage, July to October) are largely grey, with a reddish-brown head, white chin, and white secondary feathers on the wing. Juveniles (both sexes) are similar to adult females but also show a short black-edged white stripe between the eye and bill. The bill and legs are red to brownish-red, brightest on adult males, dullest on juveniles.[2][3][4]

Contents

Taxonomy

Male Mergus merganser americanus

There are three subspecies, differing in only minor detail:[2][3]

  • M. m. merganser Linnaeus, 1758. Throughout northern Europe and northern Asia.
  • M. m. orientalis Gould, 1845 (syn. M. m. comatus Salvadori, 1895). Central Asian mountains. Slightly larger than M. m. merganser, with a slenderer bill.
  • M. m. americanus Cassin, 1852. North America. Bill broader-based than in than M. m. merganser, and a black bar crossing the white inner wing (visible in flight) on males.

Behaviour

M. m. merganser, female
Couple and single female on Jona (river) in Switzerland

Like the other mergansers, these fish-feeding ducks have serrated edges to their bills to help them grip their prey; they are therefore often known as "sawbills". In addition to fish, they take a wide range of other aquatic prey, such as molluscs, crustaceans, worms, insect larvae, and amphibians; more rarely, small mammals and birds may be taken.[2][3] As in other birds with the character, the salmon-pink tinge shown variably by males is probably diet-related, obtained from the carotenoid pigments present in some crustaceans and fish.[5] When not diving for food, they are usually seen swimming on the water surface, or resting on rocks in midstream or hidden among riverbank vegetation, or (in winter) on the edge of floating ice.[2][3]

M. m. americanus, female and juveniles

Nesting is normally in a tree cavity, thus it requires matures forest as its breeding habitat; they also readily use large nest boxes where provided, requiring an entrance hole 15 cm diameter.[6] The female lays 6–17 (most often 8–12) white to yellowish eggs, and raises one brood in a season. The ducklings are taken by their mother to rivers or lakes immediately after hatching, where they feed on freshwater invertebrates and small fish fry, fledging when 60–70 days old. The young are sexually mature at two years old.[2][3][4]

The species is a partial migrant, with birds moving away from areas where rivers and major lakes freeze in the winter, but resident where waters remain open. Eastern North American birds move south in small groups to the United States wherever ice free conditions exist on lakes and rivers; on the milder Pacific coast, they are permanent residents. Scandinavian and Russian birds also migrate southwards, but western European birds, and a few in Japan, are largely resident. [2][3] In some populations, the males also show distinct moult migration, leaving the breeding areas as soon as the young hatch to spend the summer (June to September) elsewhere. Notably, most of the western European male population migrates north to estuaries in Finnmark in northern Norway (principally Tanafjord) to moult, leaving the females to care for the ducklings. Much smaller numbers of males also use estuaries in eastern Scotland as a moulting area.[4][7][8]

Status and conservation

Overall, the species is not threatened, though illegal persecution by game fishing interests is a problem in some areas.[9]

Within western Europe, there has been a marked southward spread from Scandinavia in the breeding range since about 1850, colonising Scotland in 1871, England in 1941, and also a strong increase in the population in the Alps.[4]

The Goosander is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.

References

  1. ^ BirdLife International (2004). Mergus merganser. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 11 May 2006. Database entry includes justification for why this species is of least concern
  2. ^ a b c d e f Hoyo, J. del, et al., eds. (1992). Handbook of the Birds of the World, vol. 1. Barcelona: Lynx Edicions. pp. 626. ISBN 84-87334-10-5. 
  3. ^ a b c d e f Madge, S. and Burn, H. (1987). Wildfowl: An Identification Guide to the Ducks, Geese and Swans of the World. A & C Black. ISBN 0-7470-2201-1. 
  4. ^ a b c d Snow, D. W.; & Perrins, C. M. (1998). The Birds of the Western Palearctic (Concise Edition ed.). Oxford: Oxford University Press. ISBN 0-19-854099-X. 
  5. ^ Hudon, J., & Brush, A. H. (1990). Carotenoids produce flush in the Elegant Tern plumage. The Condor 92 (3): 798-801.
  6. ^ du Feu, C. (2005). Nestboxes. British Trust for Ornithology Field Guide Number 23.
  7. ^ Little, B. & Furness, R.W. (1985) Long distance moult migration by British Goosanders Mergus merganser. Ringing & Migration 6: 77–82.
  8. ^ Hatton, P. L., & Marquiss, M. (2004). The origins of moulting Goosanders on the Eden Estuary. Ringing & Migration 22: 70–74.
  9. ^ Crimes against birds. Partnership for Action Against Wildlife Crime in Scotland.

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