Date: 12/30/20 11:56 am
From: Derek Lecy <dlecy25...>
Subject: Re: [cobirds] Why Female Red-winged Blackbirds only?
Hi All,

I'm out here in the Bay Area, CA but this topic recently surfaced with
regards to observers noting that Red-winged Blackbirds appear in single-sex
flocks near the coast in winter. Alvaro Jaramillo, who literally wrote the
book on New World Blackbirds (*icterids*), noted the following.

*Often they are in all female flocks around here, and only in winter. The
males are not as common on the coast as the females, but they are frequent
in the Central Valley in winter. Again, they segregate in winter into
single sex flocks.*

When asked if Tricolored Blackbirds segregate into single sex flocks, this
was Alvaro's response:








*It is a classic Red-winged behavior, it seems to me that
Tricoloredblackbirds are mixed but in general I see a preponderance of
males on thecoast. Yellow-headed Blackbirds also segregate, it would be
interesting tosee what Great-tailed Grackles do in areas where they are
common. The reasonis that sexual size dimorphism may be one of the factors
in sex segregatedflocks. Certainly oropendolas in the Neotropics segregate
during thenon-breeding season, and they have the largest size dimorphism of
any bird.Great-tailed grackles are not too far behind.*

I hope this info is of interest.

Regards,

Derek Lecy
San Rafael, CA (but born and raised in Boulder)
On Tuesday, December 29, 2020 at 11:43:49 AM UTC-8 <charles......>
wrote:

> All males here as well, both along the South Platte in Denver and on the
> Barr Lake CBC. Definitely a mix of young and adult plumaged birds. And
> try as I might none of them could be converted to Rusty's.
>
> Charlie Chase
> Denver
>
>
>
> On Tue, Dec 29, 2020 at 11:12 AM W. Robert Shade III <wrsh......>
> wrote:
>
>> I have as many as 50 or more Red-winged Blackbirds swarming my feeders
>> every morning. Why are they all females? Males do not look like females in
>> winter do they? This means they must spend the winter in different places.
>> If so, what is the rationale for that? I cannot think of any other species
>> that segregates by gender in winter.
>>
>> Bob Shade
>> Green Mountain
>> Lakewood
>>
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