Having banded hundreds of both purple and Cassin's finches we do not believe
that streaking on the under-tail coverts if a confirmation of Cassin's rather
than purples... There is a lot of variability on that feature. We have
had Cassin's with no streaking and purples with light streaking. We band
North of Blewett/Swauk Pass near Camas Meadows and Have flocks of both in that
area.