Subject: Re: TWEETERS digest 1142
Date: Sep 4 00:38:18 1997
From: jcbowling at mindlink.bc.ca - jcbowling at mindlink.bc.ca


** Howard F. wrote -


> About red-eyed vireos --> On the way to the Spokane office this
> Wednesday morning I stopped off at a nice little Cottonwood/Aspen
> stand (north of Spokane off of Hwy 2) and saw between 50 - 60
> Red-eyed vireos along with 25-30 Western tanagers, cedar waxwings,
> some common yellowthroats and yellow warblers. This is the most
> red-eyed vireos and western tanagers I have ever seen together!
> Almost all of the red-eyed vireos appeared to be this year's birds - all
> were in fresh plumage having vivid bright colors. I believe that the after
> hatch year birds (AHY) would not have completely molted yet. Is this
> true?

There were more Red-eyed Vireos in the c. interior of BC this past summer
than ever before. People from other inland areas report the same thing. Not
sure about the coast. If one were to crunch the various Breeding Bird Survey
numbers, I'm sure that this species would have shown the biggest jump from
the longterm averages. Conversely, Yellow Warblers were down just about
everywhere.

Which gets us back to cowbirds once again: both these species are well-known
cowbird hosts. If one were to assume, rightly or wrongly, that cowbirds are
one of the main checks on these species' populations, then one could posit
that Yellow Warblers are being more negatively affected than Red-eyed Vireos
these days by cowbird hosting. If so - why?

As for molting chronology, not sure about Red-eyed Vireos but the "Birds of
N. America" monograph on Philadelphia Vireo states that Definitive Prebasic
Molt for adults occurs in late July and August. It states that for this
species, birds of the year replace all their feathers *except* remiges and
retrices in the postjuvenal (= prebasic 1) molt during this same time period.

- Jack






Jack Bowling
Prince George, BC
jcbowling at mindlink.bc.ca