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 Tricolored
blackbirds are mixed but in general I see a preponderance of males on the
coast. Yellow-headed Blackbirds also segregate, it would be interesting to
see what Great-tailed Grackles do in areas where they are common. The reason
is that sexual size dimorphism may be one of the factors in sex segregated
flocks. Certainly oropendolas in the Neotropics segregate during the
non-breeding season, and they have the largest size dimorphism of any bird.
Great-tailed grackles are not too far behind.
blackbirds are mixed but in general I see a preponderance of males on the
coast. Yellow-headed Blackbirds also segregate, it would be interesting to
see what Great-tailed Grackles do in areas where they are common. The reason
is that sexual size dimorphism may be one of the factors in sex segregated
flocks. Certainly oropendolas in the Neotropics segregate during the
non-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...@gmail.com 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 ChaseDenverOn Tue, Dec 29, 2020 at 11:12 AM W. Robert Shade III <wrsh...@gmail.com> 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 ShadeGreen MountainLakewood--You received this message because you are subscribed to the Google Groups "Colorado Birds" group.
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