>To what extent do hummingbird hybridize?

There are a lot of records of hummingbird hybridization, probably more than
in the average family. A paper published some time ago (Sibley, C. G.
1957. The evolutionary and taxonomic significance of sexual dimorphism in
birds. Condor 59: 166-191.) came up with the hypothesis that hummer
hybrids, even intergeneric ones, are relatively common because sexual
selection has produced dramatic differences among males in groups of
species that are quite closely related and little different genetically.
He thought the substantial rate of hybridization in ducks was additional
evidence for this.

The Banks and Johnson paper that Chris Hill mentioned discussed a bunch of
hybrids, but not Black-chinned X Costa's. The Short and Phillips paper did
discuss that hybrid, a male and a female, with detailed descriptions. The
Wells et al. paper discussed Anna's X Costa's hybrids. From my brief
perusal of the BCHU X COHU description, that bird (a specimen) was a lot
more intermediate than the one you describe. Costa's is closer in size to
Black-chinned than to Calliope, and the skins in our collection, in fact,
look the same size, so the size comments you made aren't compelling to me.
Why not just a Costa's?

The nice thing about a bird in hand, as opposed to a bird at a feeder, is
that measurements can be taken and the details of shape of the primaries
and rectrices that are important in distinguishing these species can be
seen. If the bird could be captured and thoroughly photographed and
measured, you might get somewhere with the identification.

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