Even if you already feel pretty secure in separating female Purple
and Cassin's Finches visually, take a look at an excellent article by
Alvaro Jaramillo and David Beadle in the latest issue of Birders
Journal (vol. 8, pp. 288-295). You may find your confidence shaken a
bit at first but be assured that further reading will restore it,
stronger than ever. The authors present an array of characteristics
to look for that reliably separate these species, going way beyond
the popular identification literature. Many of the best
characteristics are structural (curve of the culmen, primary
projection). The prominent white supercilium of female Purple Finch,
emphasized in so many field guides, is characteristic of "Eastern"
Purple Finch (Carpodacus purpureus purpureus) but is only marginally
useful as a field mark here in western Washington where the resident
populations are an even darker version of the already relatively dark
"California" subspecies (C. p. californicus), which has diffuse
streaking and facial markings. One the other hand, the white eye
crescents of female Cassins's are surprisingly distinctive.
Vocalizations are also discussed. Most birders around here have
learned from personal experience that Cassin's Finch is an excellent
mimic, but so it appears is the "California" Purple Finch. The
article is illustrated with seven photos of birds in the
hand--sometimes with the two species side by side in the same
photograph--and a fine gouache plate by Beadle. The treatment also
includes House Finch.

If you bird with any frequency in central Kittitas County, you have
no doubt discovered that Purple Finch is a fairly common breeding
species in a broad belt from north to south, embracing the Ponderosa
Pine and Interior Douglas-fir Zones. There you may find both Purple
and Cassin's side by side, with House Finches thrown in locally
around towns and farm buildings. This is surely the best place in
the state to practice sorting these species out.

Hal Opperman
Medina, Washington
mailto:halop at acccessone.com