[obol] Re: Possible Bronzed Cowbird
- From: "Wayne Hoffman" <whoffman@xxxxxxxx>
- To: <llsdirons@xxxxxxx>, "'OBOL Oregon Birders Online'" <obol@xxxxxxxxxxxxx>
- Date: Fri, 31 May 2013 19:34:03 -0700
Hi -
I have some experience with Bronzed Cowbirds As winter vagrants in Florida,
and they had fully red eyes whenever we saw them Nov., Dec., Jan., Feb.
Wayne
From: obol-bounce@xxxxxxxxxxxxx [mailto:obol-bounce@xxxxxxxxxxxxx] On Behalf
Of David Irons
Sent: Friday, May 31, 2013 8:49 AM
To: OBOL Oregon Birders Online
Subject: [obol] Re: Possible Bronzed Cowbird
Jeff et al.,
In discussions that I've had with Alvaro Jaramillo, who literally 'wrote the
book' on blackbirds and other icterids, he told me that eye color changes
very early on with male blackbirds. I also checked Birds of North America
Online and this is what their species account has to say about the eye color
transition (isn't clear on the timing):
Iris
Begins chestnut (young and juveniles), becoming mottled orange and
greenish-yellow (adult females, sub-adult males), then scarlet to crimson in
breeding males (ASY). Most color due to quantity of reflective purines and
hemoglobin in blood, not pteridines (
<http://bna.birds.cornell.edu/bna/species/144/articles/species/144/biblio/bi
b081> Oliphant 1988,
<http://bna.birds.cornell.edu/bna/species/144/articles/species/144/biblio/bi
b073> Hudon and Muir 1996). Male in breeding season: scarlet to crimson;
male in nonbreeding season and females: brownish orange to orange brown (
<http://bna.birds.cornell.edu/bna/species/144/articles/species/144/biblio/bi
b010> Dickey and van Rossem 1938).
As to the bull-headed shape and ruff, this may be more of an ASY (after
second year) trait and not necessarily evident in a first-year male.
Presuming that most first-year males don't breed-hence no need for the ruff
(used for display)-the extra feathering that produces the ruff effect may
not be acquired until the bird's second complete (prebasic) molt, which
occurs about 18+ months after hatching. Blackbirds are really variable, with
feather wear playing a major role in appearance. That said, I cannot find
any references to black-headed Brown-headed Cowbirds. This might be a photo
that we want to post to ID-Frontiers. It's a head-scratcher.
Dave Irons
Portland, OR
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