White-winged Scoter taxonomy

and vagrancy…

Scoters. Painted by  Henry Thurston for Jonathan Dwight’s 1914 paper. (see below) Back then all 3 Scoters with white wings were split as separate species.

This is the guts of the text from ‘Frontiers in Birding’ on the subjects of Vagrancy and Taxonomy.

Vagrancy:

Velvet Scoter in North America

Velvet Scoter has reached Greenland (Witherby et al. 1944), and thus seems a likely potential vagrant to North America.

White-winged Scoter in Western Europe

Iceland is the only country so far in the Western Palearctic with confirmed records of White-winged Scoter. Since the first, at Arnarfjordur, northwest Iceland, in June 1993, there have been five accepted records, all in the period May to July including one adult male, which paired with a female Northern Eider (Kolbeinsson et al. 2001). There have also been several records of White-winged Scoter (deglandi) in northeast Asia (Dementiev & Gladkov 1967).

Postscript. Hard to tell exact number of individuals involved due to repeat appearances. It is claimed from 2-8 birds have occurred. Iceland is now no longer the only place that White-winged Scoter as occurred in the W. Palearctic (as of last Saturday!).

Stejneger’s Scoter in Western Europe

There have been four extralimital records of Stejneger’s Scoter in Europe, two of which were initially misidentified, perhaps suggesting that others have been overlooked. The records, all of adult males, are as follows: Baie de Somme, northern France, 4th December 1886 (recently re-identified specimen: Jiquet 2007); Kemio, southwest Finland, May to June 1996 (Lindroos 1997); Iceland, April to May 2003 (Garner et al. 2004); Gdansk Bay, Poland, 10th March 2007 (photographed, Dorota Lukasik pers.comm).

Postscript: Adult male Rossbeigh Strand, co. Kerry, Ireland  winter 2010/2011

Short clip of Stejneger’s in Mongolia taken by James Lidster last week.

Stejneger’s Scoters in North America

Until recently there were no records of Stejenger’s Scoter in North America. In early June 2002, while leading a bird tour to Gambell, Alaska, Jon Dunn, Steve Howell and Gary Rosenberg found a ‘White-winged’ Scoter swimming off the northwest tip of St Lawrence Island. They had witnessed a small, but consistent, spring passage of White-winged Scoters in late May and early June in each of the previous twenty-five years they had collectively led tours to Gambell, but this was the first time that a swimming bird had been found there. JD was the first to notice that this male-plumaged bird had ‘black’ flanks, unlike normal deglandi White winged Scoters from the mainland. The bird remained off the point for at least three days (2nd-4th June), and photographs were taken by GR. Shortly thereafter, GR photographed normal deglandi in the interior of Alaska, from which differences in bill colouration and structure were noticed. Further direct comparison of the photographs of the Gambell bird with photographs of stejnegeri in a photographic guide of the birds of Japan confirmed that the Gambell bird was an example of Stejenger’s Scoter.

This record was subsequently pre-dated when a photograph was discovered of an adult male Stejneger’s Scoter taken at Cape Nome, Alaska, by Brad Bergstrom on 30th May 2001 (Garner et al. 2004). Given this overlooked record and the fact that most birds are seen only in flight off Gambell (see above), it seems likely that Stejneger’s Scoter actually occurs more commonly in North America.

Taxonomy

In a paper published back in 1914 Henry Thurston illustrated not 3 but 6 species of Scoter (see Dwight 1914). Under the genus of Oidemia the six recognized species were:

Oidemia americana = Black Scoter

Oidemia nigra = Common Scoter

Oidemia fusca = Velvet Scoter

Oidemia deglandi = (American) White-winged Scoter

Oidemia carbo = Stejneger’s Scoter or Asian White-winged Scoter

Oidemia perspicillata = Surf Scoter

Since then the genus has changed to Melanitta and in the ‘west’ the 6 Species were lumped into 3 Species during the early/ middle part of the 20th Century. With some bird forms there have been genuine discoveries in the last couple of decades about biology, behaviour and characteristics (including molecular data) that have caused an elevation of a former subspecies to species status. Examples such as Taiga Flycatcher, Balearic Shearwater and Hume’s Warbler spring to mind. However some taxonomic changes, and are more of a pendulum swing simply reflecting current trends rather than new information, and this is certainly more the case with the Scoters. Past authors such as Dwight fully recognized the very significant differences in bill structures, feathering around the bill base and some plumage differences that caused them to see specific status for these birds as axiomatic.  More recently the BOURC split Black Scoter and ‘American’ White-winged Scoter (Collinson et.al. 2006), and the criteria used are largely the same as those evident in Dwight (save for difference in courtship call between Common and Black Scoters).

Russians ornithologists have had these species splits in place for many years. Here is how the taxonomic situation looks currently under the BOURC:

Melanitta americana = Black Scoter

Melanitta nigra = Common Scoter

Melanitta fusca = Velvet Scoter

Melanitta deglandi (ssp. deglandi and stejnegeri) = (American) White-winged and Stejneger’s Scoter

Melanitta perspicillata = Surf Scoter

It may sound presumptuous, but by simply applying established criteria (Helbig et al. 2002) it is clear that all 3 forms of ‘white-winged Scoter’ display more than sufficient criteria for them all to be classified as full species. They well-defined biological and evolutionary species. It is anticipated that any DNA/Phylogenetic studies will further establish this taxonomic position.

All three taxa are diagnosable in the field and exhibit differences at all ages and in all plumages (e.g. Dwight 1914, Witherby et al.1944, Cramp & Simmons 1977, Gardarsson 1997, Garner 1999, Garner 2004). They also appear to be reproductively isolated: they have essentially separate breeding and wintering ranges, and there is no evidence of interbreeding or clinal variation. Thus, according to the criteria proposed by Helbig et al. (2002), they can justifiably be classified as three separate species:

Velvet Scoter Melanitta fusca (Linnaeus 1758)

White-winged Scoter M. deglandi (Bonaparte 1850)

Stejneger’s Scoter M. stejnegeri (Ridgway 1887)

References

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Cramp, S. & Simmons K.E.L. Eds. 1977. The Birds of the Western Palearctic. Vol. 1. Oxford.
Dementiev, G.P. & Gladkov, N.A. Eds. 1967. Birds of the Soviet Union. Vol. 4. Jerusalem.
Dwight, J. 1914. The moults and plumages of the Scoters, genus Oidemia (Melanitta). Auk 31: 293-308.
Gardarsson, A. 1997. Korpönd að vestan. Bliki 18: 65-67.
Garner, M. 1999. Identification of White-winged and Velvet Scoters – males, females and immatures. Birding World 12: 319-324.
Garner, M., Lewington, I. & Rosenberg, G. 2004. Stejneger’s Scoter in the Western Palearctic and North America. Birding World 17 (8): 337-347
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