Dutch Birding volume 24 (2002) no 2

Female mystery eider at IJmuiden in January 1987

The identification of an adult female Common Eider Somateria mollissima photographed at IJmuiden, Noord-Holland, the Netherlands, on 20 January 1987 is discussed. The bird showed a number of King Eider S spectabilis features like a rounded point to the feathering on the lores, frontal processes not coming close to the eyes (possibly explaining a rather hooked forehead profile) and possibly a dark bill-tip. However, unlike a typical female King Eider, the bird did not show an upturned gape, lacked a contrasting pale loral area and eye-ring, and had a closely barred plumage pattern without King Eider's open U-shaped flank-barring. Nevertheless, the bird seemed to be at variance with European Eider S m mollissima (the only subspecies recorded in the Netherlands). Some features, like the round loral feathering shape, apparent short frontal processes, pale plumage and possibly dark bill colour, may suggest Pacific Eider S m v-nigra which breeds, isolated from other subspecies, from north-eastern Siberia east to north-western Canada, and winters in the Bering Sea. Vagrancy records of Pacific are from as far afield as Greenland and Newfoundland, Canada, but there is no European record. Boreal ('East Arctic') Eider S m borealis seems to be a more likely candidate to occur as a vagrant in the Netherlands (there is one record for Britain) but, on average, that taxon should have a less rounded, deeper loral feathering and darker plumage. Unfortunately, the shape of the frontal processes (narrow and pointed in Pacific) is hard to judge from the photographs. Because of bill shape and general colour, a hybrid Eider x King Eider has also been considered. In Iceland, for instance, such hybrids are known for males (37 records) but there are no records for females (although occasionally female birds are seen that are suspected to be hybrids). It is concluded that, at least for the time being, it remains uncertain whether the IJmuiden bird was a European Eider with an aberrant bill, a vagrant subspecies or a hybrid Eider x King Eider.

Arnoud B van den Berg, Duinlustparkweg 98, 2082 EG Santpoort-Zuid, Nederland
arnoud.vandenberginter.nl.net