Friday, July 1, 2011

Cassin's vs. Purple Finch

A large flock of Cassin's Finches were the highlight of our friend's Missoula feeder. Identifying Cassin's Finches turns out to be more complex than I first thought.  Even a Cornell website concludes that separating Cassin's and Purple finches can be extremely difficult. I needed all of my identification guides to ferret out the differences, with no one guide giving definitive advice.
The two photos above are of male Cassin's Finches.  The photo immediately below is of a male Purple Finch.  The salient field marks of male Cassin's Finch are as follows:

1.) The red tends to be much brighter than the rest of the head, giving it an almost redpoll appearance.  Purple Finch heads are more uniformly colored.

2.) Cassin Finch bills tend to be straigher and sharper, more like a siskin.  Compare the first and third photographs.  The top of the upper bill of the Cassin's finch tends to be straighter, at least until the very tip.  In contrast, the Purple Finch's bill is shorter and tends to be uniformly curved on the top.

3.) The lower flanks of the Cassin's Finch have fine brown streaks.  What streaks there are on a Purple Finch tend to be blurrier and reddish.

4.) Male and female Cassin's Finches tend to have a thin white eye-ring, absent in Purple Finches.

5.) My photos indicate that Cassin's Finches' breasts have a slightly different red hue.

Other field marks mentioned in various field guides, but they do not seem to be evident in my photographs.  Peterson's Western Birds indicates that the Purple Finch's nape is reddish.  My photo shows a Purple Finch with a brownish nape.  On the other hand, Sibley's Birds of North America does not depict the distinct brownish malar streaks on male Cassin's Finches, while Peterson's illustration does.
The next two photographs are of female finches, first Cassin's and, finally, Purple.

1.) The bills sort out similar to the males'--pointy and siskin-like in the Cassin's, stubbier and chunkier in the Purple.

2.) The streaks on the underparts differ. The Cassin's streaks are crisp and dark.  The Purple's streaks are fuzzier and more diffuse.

3.) Again, Cassin's Finches tend to show a thin, white eye-ring.

Some field guides suggest that the facial pattern is less distinct on the female Cassin's Finch.  My photos shed some doubt on this mark as being really useful.  The Cassin's Finches we saw appeared to have more white around their eyes. House Finches are also similar to Cassin's and Purple finches, and were also present at the Missoula feeder.  Previously I have blogged on the identification of Purple and House finches.
Minnesota birders may wonder why one would blog at such length on this subject.  The closest Cassin's finches breed to Minnesota is in the Black Hills of South Dakota. They breed in the Rocky Mountains.  Minnesota birders should take note. We have at least one record of a Cassin's Finch, a bird found at a Duluth feeder in November 1986 (Eckert, A Birder's Guide to Minnesota Birds).

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