Hi All - This is somewhat off-topic, but I hope it is relevant anyway.

About 11 years ago, when Toni and I were just getting started with birding,
we were fortunate to see a couple of male Eurasian Wigeons at Pea Island NWR
(NC).  They had the red sides on the head and the golden yellow crowns that
are illustrated in all the books.  (We've seen a few additional Eurasians
since then.)

The next day, at the same place, we saw more wigeons.  A few of them, when
initially seen from the front, showed golden yellow crowns, so we assumed
that they were Eurasian - until they turned sideways and we saw that the
sides of their heads were clearly green.  We were assured by experienced
birders that they were American Wigeons, so we assumed that the apparent
yellow crowns were a trick of lighting - the Sun was low behind us.

I haven't seen that yellow crown effect on American Wigeons since then,
until last week, when I was birding in (the state of) Washington, between
Vancouver and Seattle.  There I saw a couple of large flocks of American
Wigeons, numbering 500-1000 (no Eurasians).  The thing that amazed me was
that at least half, maybe 3/4 (but not all), of the males had golden yellow
crowns.  In this case, it wasn't a lighting effect - it was quite overcast.

Can someone enlighten me on what causes this?  A dietary effect?  Or were
those maybe very young birds?  (Would they dominate numerically?)  I don't
think it is illustrated in any book I've seen.  They don't look at all like
the hybrids pictured in Sibley.

Thanks,
    Bob Hartman