I didn't see any replies to this question so I thouht I would field it.
Fringillids, in general, are poor hosts for cowbirds. Both House
Finches and American Goldfinches have been studied and both do not raise
cowbirds to fledgling. In both cases, they feeding their young seeds and
the young cowbirds starve to death (they require insects to grow). I don't
know of any research with other fringillids such as siskins, rosy-finches,
crossbills, Evening Grosbeaks, or Pine Grosbeaks. I don't think Pine
Siskins would be good hosts but it would depend on what they feed their
nestlings. If they feed them seeds, they couldn't raise cowbird chicks. If
they feed their chicks insects, it is possible for them to raise cowbird chicks.
My best guess would be that the siskin was just responding to the
begging behavior of the cowbird. There are many published accounts of adult
birds feeding fledglings that were not their own. There is even a published
report of an American Robin feeding a goldfish in a garden pond! It is
thought that the adult birds simply can't ignore begging young.
I will try to remember to look up records of Pine Siskins raising
cowbirds.

Cheers
Deb


At 10:33 AM 08/07/98 -0700, you wrote:
>At our feeder today we saw a Pine Siskin feeding a begging juvinile
>Brown-headed
>Cowbird. Is it possible that the PISI raised the BHCO, Or was the PISI
>just responding to the begging, and It happened to be a BHCO.
>
>Jerry and Sandy Converse
>Grand Coulee, WA
>
>
Deborah K. Beutler
Department of Zoology
Washington State University
Pullman, WA

dbeutler at wsunix.wsu.edu