mandag den 2. april 2012

Presumed Northern Eider (S. m. borealis), 1.4.2012, Hanstholm Havn

This ‘presumed to be’ of the form borealis also known as ‘Northern Eider’ was found feeding in Hanstholm Harbour by Jeppe Bundgaard, Peter Bundgaard, Henrik Læssøe and me on 1st April 2012. It could become the first Danish record and it feels great finally to find one with white sails following my 2009 attempt.

It was really a stunning Eider and was quite easily recognised in comparison with the two Common Eiders occasionally swimming next to it. Superficially it is very similar to the dapper black and white plumage of Common Eider but it is the small ‘scapular sails’ and also the bright yellow tones of the bill that really set them apart.

The ‘Northern’ form also known as ‘Borealis’, (which is also the Latin name Somateria mollissima borealis) is basically the name given to the subspecies in the Arctic regions of the North Atlantic, from North East Canada, Greenland, Iceland and Svalbard. There are several subspecies in the ‘Common Eider’ group; besides the Common Eiders (S. m. mollissima) there are three of which we should be (and many are) on the lookout for as they could potentially turn up as vagrants.

Livezey (1995) suggests that the Common Eider is actually four species: S. v-nigrum (Pacific Eider), S. borealis (Northern Eider), S. dresseri (Canada/American Eider) and S. mollissima (European Eider). ‘Northern’ Eider is by far the most likely target and it is possible and indeed quite likely that birds have been over looked in Denmark in the past.

According to Garner (2008), Garner & Millington (2010) and Van Duivendijk (2010) the key features of adult male Northern Eider in relation to European Eider are:

  • Two stiffer modified long scapulars creates presence of white sails on the back
  • Colour on the bill base, many have orange tones over the bill base
  • Legs and feet colour match the bright yellowish orange tones of the bill base
  • The feathered black stripe running down the side of the bill lobe is very narrow
  • The feathered white area on the side of the bill is more pointed and lack the rounded tip
  • The lobes differ in shape being more pointed
  • Bill shape differ structurally tending to be more elongated and drooping towards tip
  • Black cap often has a straight lower edge
  • Head shape tend to be squarer with steeper forehead
  • Breast can be richer, deeper salmon colour

The Northern Eider appears to occur annually off the northern coasts of Britain and Ireland. The origin of these birds remains uncertain but, in terms of movement and migration, birds from Canada, Greenland, and maybe Spitsbergen, could all occur within our area.

This image shows how in really good contenders for borealis Eider, the leg and feet colour should match the bright yellowish orange tones of the bill.

See this photo indication of positive borealis characters.

Nice rich yellowy bill, extra wings/nipples/spurs/sails/fins (whatever you want to call them) protruding from its back, “English Mustard” coloured legs and feet and narrow black running down the sides of the bill lobes. The lobes too differed in shape from the other “Common” Eiders, so it ticked the boxes in terms of sub ‘specific identification.




There is a cline in bill colour and frontal lobe shape from east to west, birds in east (Svalbard and some in Iceland) with olive-grey bills and fine and pointed frontal lobe, and birds in west Greenland and northeast Canada) with increasingly bright and orangey bills and slightly broader and round-ended lobe. Leg and foot colour usually mirror bill colour in that birds with dull olive bills have dull yellowy-olive legs while birds with the brightest yellow or yellow-orange bills tend to have the brightest yellow-coloured legs and feet.

All male eiders have two stiffer modified long scapulars. They are the same feathers that give male King Eider their permanently erect black sails. So far it seems that only vagrants to Western Europe from further north and west have obvious white sails and they are presently considered to be a guarantee of Arctic or Nearctic origin.

This image shows how the bill shape tends to differ structurally as well as by colour, tending to be more elongated and drooping towards tip.

The difference in bill colour to the accompanying Common Eiders is quite distinct. The shape of the lobes (the extremity of bill that runs up towards forehead) tends to be different as does the black that borders it...










References

Garner, M. 2008: Frontiers in Birding. BirdGuides Lft., Sheffield.
Garner, M. & Millington, R. 2010: The forms of Common Eider: their identification, taxonomy and vagrancy. Birding World 23(2): 65-82.
Livezey, B.C. 1995: Phylogeny and evolutionary ecology of modern seaducks (Anatidae: Mergini). Condor 97: 233-255.
Van Duivendijk, N. 2010: The Advanced Bird Guide: ID of Every Plumage of Every Western Palearctic Species. New Holland, London.

1 kommentar:

Henrik Læssøe sagde ...

fine billeder Kent
vh Henrik Læssøe