>Ten to twenty years ago, we rarely saw or heard black-headed grosbeaks in
>Western Washington. Now they appear to be relatively common, even
>patronizing our feeders. Has this been observed by others, or can anyone
>offer an explanation for the change?
>
>Bill and Erin Woods Woods Tree Farm Redmond, WA U.S.A.
><wwwbike at halcyon.com>

Yes, and yes.

This is a species that is increasing in the Northwest, according to the
Breeding Bird Surveys. It is characteristic of riparian, broadleaf, and
mixed woodland, and, apparently, at least some of the habitats that it
likes are increasing.

I'm never shy about speculation, and in this case I would hypothesize that
precaucasian Cascadia was too dense and coniferous for this species (they
were probably along the rivers), early Caucasian Cascadia was clear cut,
still not appropriate habitat (they need fair-sized trees), and present day
has seen the clear cuts grow up, many of them with alders and maples, and,
perhaps not inconsequential, urban neighborhoods become more and more
wooded (except Ballard). We have BHGR singing in the ravine behind the
house every spring/summer, but I'm not convinced they've ever bred; perhaps
only a single misdirected male. In birds, females seem better able to
choose appropriate real estate.

Alternatively, something is changing about its northern Mexican wintering
habitat that favors this species. The interesting and almost mind-boggling
aspect about this is that, for a migratory bird, you would think that both
ends of the migration route would have to become more favorable for an
increase to occur. Alternatively, the bird was limited at one end and thus
not at the carrying capacity of the other end, in other words, not as
common as it could be. Then when conditions become better at the limiting
end, the bird will increase at the other end too. Is this clear?

Then again, others might argue that grosbeaks are being driven from their
"wild" forested habitats and are becoming more common in the suburbs. Or
that, with global warming, what was once the periphery of the range is now
being filled in. Any sign of range extension to the north, British
Columbians?

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416