Nagi, your picture shows a classic Lesser Scaup, no ambiguity about it. When my
dad hunted scaup on Long Island Sound the Connecticut Fish and Game employee
used the measure of nail width on bills to distinguish the two species, but he
was using calipers. This scaup is alive and well, so its head profile affords a
good ID: somewhat flattish top to head, decided crested look at the nape.
Greater Scaup typically have a smooth curve there at the nape, with possibly a
slight angular break in that curve of the profile nearer the top of the head.
Please correct me if I'm wrong folks, but isn't the default scaup in
shallow fresh water in western Oregon in winter the Lesser? And winter scaup on
salt water in winter are typically Greaters in Oregon. I think the Coos Bay CBC
got one Lesser this year and it was in a pond in a city park. Visitors to the
Philomath Sewage Ponds this winter have occasionally scrounged up one or two
Greaters among the scores of Lesser Scaup. The head shape works to ID female
scaup as well. It is fraught with challenges, as shown in Sibley. Ducks just
before or after diving, when preening, what have you, do all kinds of things
with their head feathers that can change the profile in amazing ways. Scaup go
through a highly uncoordinated molt. I've seen birds throughout the winter that
are way ahead or behind their fellows in the succession from eclipse to full
breeding plumage.
That's why I say your picture shows a classic individual. A soft field
mark for sure, but the others that come to mind are less useful. LarsPOST:
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