A very troublesome scaup - Ohio, March 5, 2023 (1 Viewer)

[qwerty5]

Hello, I saw this scaup diving about 30 ft away the other day. I originally ID'd it as a Lesser, because when relaxed the head looked too tall for a Greater. However, after reviewing my digiscope pics, I've been flipping back and forth between which species I think it is. I've read all the info online and in books that I can get my hands on but I still cant decide. The photos can be found here. This bird was actively diving, so it obviously flattened its head feathers down, as can be seen in the later photos. However, what I noticed in the photos is that even when the head feathers are obviously raised, there still is no peak at the rear of the head as one would expect for Lesser. Unfortunately, in the picture of the bird with the feathers raised farthest, the bird is looking away. As I said the reason I initially ID'd it as a Lesser is because the head looked too tall for Greater, I never saw a peak at any point during my observation. Also the head looks like it might be too thin for Greater. Anyways, the best points are probably bill size and shape, which I do not feel experienced enough to judge. Any help is appreciated.

P.S. I measured and the eye is positioned very close to the middle of the head with the feathers raised. According to Tony Leukering this is indicative of Lesser, but I still can't escape the lack of a peak.

 

[THE_FERN]

It's "clearly" (!?!) a greater for me. Head shape very different to what I'd expect for lesser

 

[nartreb]

If I had to guess, I'd say Greater: back of head smoothly rounded, no peak. Very large white patch at base of bill (not diagnostic, but indicative). I know Greater is supposed to have a wider bill than Lesser but I have never been able to see this for myself.

 

[qwerty5]

Here are two more pictures not on the checklist which may or may not provide any insight. I believe the bill differences are supposed to be that Greater's is wider and has a more bulbous tip when viewed from front, and when viewed from the side, Greater's appears deeper and larger, and less concave. But it's all theoretical to me, I don't have the experience to consistently see a difference.
Anyway it looks like I should forget my initial impressions of Lesser.

 

[Butty]

Probably greater scaup: rounded rear of head, big bill.

 

[qwerty5]

Greater it is then, thanks for the help.

 

[KC Foggin]

After all the Google searching, I go with Greater! Nice photos too!