Hello, tweets.

I'll add a little info to my post about Eurasian Wigeons, which I'm
tickled to see has stimulated so much response.

I have spent a lot of time watching male Eurasians in late winter/
spring to see if they were mated, and many of them aren't. You can
usually fairly easily determine this by watching birds in small
flocks to see which of them tend to be hanging out in pairs. This, in
addition to seeing relatively few of the very obvious rufous morph
females, is what has made me conclude there are a lot fewer females
than males. I have also looked for gray morph females, which are more
similar to American females but still distinguishable, as they don't
show the contrast between head and body typical of female Americans.
I have also seen male Eurasian seemingly mated with what I was pretty
sure were female American, and the frequency of observed hybrid males
indicates this occurs with some regularity. It would also be
predicted if female Eurasians were hard to find.

In the flock of wigeons that excited me, there would be 5-10 male
Eurasians in a row as I scanned, with no females nearby, and that
doesn't gibe with the thought that those males would have been mated.
By spring, most female ducks are mated, and that many unmated males
together tells me there are a lot more of them than females, the
ratio more extreme than in the American species (American Wigeons,
Northern Pintails, Mallards, Green-winged Teals) that we observed in
the same area on the same day.

My observations also correspond to what I know of the natural history
of ducks. Males are more prone to wandering than females (hmm, is
there a human parallel?), so vagrant ducks should more likely be
males. Of course, the fact that most of the vagrant ducks we see are
males may only be because females would be a lot harder to pick out.
But female ducks are much more philopatric (likely to return to where
they were hatched) than males, and males usually return with their
mate to the female's breeding grounds, even if they are far from
where the male hatched. Ergo, males are the dispersing sex, which
should mean they are more prone to vagrancy.

I just performed an exercise to test the hypothesis of female
Eurasians being relatively rarer than males. I looked at online
photos of Eurasian males from North America, and in the first dozen I
looked at, often with American Wigeons, I saw not a single associated
female. Many of the Americans in the same photos were probably
paired, or at least there were female Americans in the photo. I have
photographed male Eurasians here and there in Washington, and not a
single one was obviously associating with a female, although of
course I've seen such pairs plenty of times.

Whatever the sex ratio, this doesn't alter the rather amazing fact
that we have these birds in such numbers. What must be thousands of
Eurasian Wigeons migrate into North America each winter, and this is
surprising. They come presumably from Siberia, as the species doesn't
breed in North America (or there is a substantial breeding population
of them somewhere to the north that remains undetected). Think of how
many other Eurasian birds that breed in the same regions of Siberia
don't migrate to North America! The Sharp-tailed Sandpiper is another
Siberian bird that migrates into North America in fall, but they
don't seem to winter in this hemisphere, and perhaps most of those
birds head out across the Pacific Ocean as they proceed south, intent
on wintering in the "correct" hemisphere.

We also have Sandhill Cranes, Snow Geese, and Pectoral Sandpipers,
among other species, that migrate here from Siberia, but those are
all different in that they are of American origin, and after the
glaciers receded, their populations presumably spread west across the
Bering Strait into Siberia. But they still return to this hemisphere
to winter, just like breeding Bar-tailed Godwits, Red-necked Stints,
and Yellow Wagtails return from breeding grounds in Alaska to spend
the winter in Asia. To my knowledge there is no equivalent to the
Eurasian Wigeon in reverse, a North American bird breeding at high
latitude that has a respectable wintering population in northeastern
Asia.

-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net



-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman1.u.washington.edu/pipermail/tweeters/attachments/20080402/8ee75f5c/attachment.htm