Scoters at Valmont Reservoir

[kevin.ru...@gmail.com]

I went looking for the Surf Scoters and White-winged Scoters that have been reported at the Valmont Reservoir Complex. I saw 4 scoters, but I'm wondering how to tell that the females are Surf Scoters, as opposed to White-winged Scoters. I posted the linked photos to the ABA "What's This Bird?" page on Facebook and got one response (so far) saying they thought all 4 are White-winged.

Any thoughts?

https://www.fernlakephotography.com/Unlisted/2021/Scoters/n-dKZkNT/i-SqDbmf2/A

https://www.fernlakephotography.com/Unlisted/2021/Scoters/n-dKZkNT/i-HHPnz3m/A

https://www.fernlakephotography.com/Unlisted/2021/Scoters/n-dKZkNT/i-VCNvhhX/A