Speculum on female Common Eider (1 Viewer)

[Peter Audrain]

In late December, at the outlet of Scarborough Marsh into the ocean, at Scarborough, Maine, I saw several male and female Common Eiders among Common Loons, Common Mergansers, Long-tailed Ducks, White-winged Scoters, and Black Scoters.

All of the swimming female Common Eiders had two very prominent white bars visible toward the rear of their bodies. These bars aren't shown in my books. They correspond to the speculum visible on flying birds, but it bothered me that the bars weren't pictured or mentioned in my guides. I am also not sure whether or not I have seen the bars before on female Eiders (further north in Maine, in summer).

I'm attaching two pictures. The light was low—the equivalent of sunset at most other times of year or latitudes—and coming from the left. The white wing bars were easily the most noticeable field mark on these Eiders. In your experience, are these bars a standard-issue look for swimming female Eiders?

 

[Nutcracker]

Yep, standard issue, though possibly a bit more obvious than average on your birds.

 

[Andy Hurley]

It is not always obvious. I have birds from Iceland that don't show white wing bars, others do. The last is from Scotland also with white wing bars.

 

[Andrea Collins]

The white bars are the tips of the greater coverts and the secondaries. They are very variable with some suggestion that they are most prominent on older birds and mostly absent on juveniles. (info from "Wildfowl of Europe, Asia and North America" by Sebastian Reeber (Helm) and "Advanced Bird ID Handbook, Western Palearctic" by Nils van Duivendijk). My very large local population shows a lot of variation.

 

[Peter Audrain]

Thanks so much—it's great to see those closer-up photos, to hear that other people have seen this vary, too, and to hear the speculation about the bars' relation to age.

I'm thinking now that it could be related to feather wear—more than posture, which was my first guess—and so would help to age them, as your Advanced Bird ID Handbook says. If it is a product of feather wear (and its absence), it would seem possible that the birds showing the bars most distinctly were the most recently molted.

In any case, it will be something more to look for and puzzle over at different times of year.

Thank you for the help!