I've said it for years, and I'll say it again: why, after almost 40 years of birding, studying every possible resource and every possible duck, do I still have trouble with telling Lesser Scaup from Greater Scaup?
Because it's not easy, that's why.
Let me walk that back a bit. I think I've got the scaup thing worked out pretty well, finally, but many times over the years very skilled birders have debated a scaup's identity right in front of me. And it. If only they could talk. The scaup, I mean.
So. I love it when they fly, because then the uncertainty virtually disappears. If the white on the wing pushes strongly out onto the primary feathers, as in the birds above, they are Greater Scaup. If it looks more like a "speculum," they are Lesser Scaup. Or, as Sibley puts it in his second edition field guide, "more white" and "less white." Brilliant. Using this mark requires one to know where the primaries and secondaries of the wing part ways, so study your field guides diagrams on bird topography.
These Greater Scaup flew past the 8th Street jetty in Avalon, NJ yesterday. Click to enlarge.
