Mystery Bird: leucistic House Finch, Carpodacus mexicanus

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[Mystery bird] leucistic House Finch, Carpodacus mexicanus, photographed on Farm Island near Pierre, South Dakota. [I will identify this bird for you tomorrow]

Image: Terry Sohl, 16 February 2009 [larger view].

Photo taken with a Canon 50D, 400 5.6L.

Please name at least one field mark that supports your identification.

Rick Wright, Managing Director of WINGS Birding Tours Worldwide, writes:

"It's not in the book."

A birding acquaintance of mine, long since passed away, I fear, once told me about the "prairie wrens" she had discovered around her place in southwest Nebraska. As I puzzled over what these birds might have been, she cheerfully assured me that I shouldn't worry, it was a new species, not in the book.

A lot of beginning birders are less sanguine when they discover a bird that's "not in the book." How can the field guides fail? Shouldn't every bird be matchable to a photo or a painting in "the book"?

No amount of picture-matching is going to identify this bird. Instead, we need to work through it like birders.

The photo was taken in the middle of South Dakota, letting us rule out nearly 10,000 of the world's bird species (and offhand, I can't think of any exotic zoobird that looks like this, either). The bird is perched in what looks like a red cedar Juniperus, the needles of which give us a good gauge of its size: this is a smallish bird, but not tiny.

A smallish bird, perched in a conifer, in Dakota, with some red in the plumage: what else could it be but a House Finch?

Starting at the rear, we see a tail of undistinguished length and shape. The wing structure is invisible, but we can see rather plain coverts with muddy off-white tips creating dull wingbars. The tarsus is stout and dark. The belly and flanks are coarsely streaked with muddy brown, the breast dull red.

The head is somewhat square in shape but small, the bill like a thick sparrow's with a strongly decurved culmen. The eye is dark and beady, though the aberrant head plumage makes it look somewhat larger than on a typical House Finch.

So what about that head? Albinism (the absence of pigment) and leucism (the failure to express pigment fully) are both relatively frequent in birds, and most often encountered, as one would logically expect, in abundant species such as House Finch. This striking bird is a great reminder to us all to consider the bird in its entirety rather than let a single unexpected feature -- one that's "not in the book" -- throw us off course.

Review all mystery birds to date.

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Unless it's an old-word accidental, my vote is a partially-leucistic House Finch (Carpodacus mexicanus, I believe). Field marks: reddish breast, belly stripes, finch beak.

By Philip Tanimoto (not verified) on 08 Mar 2009 #permalink

I have to agree with Philip - the pink breast, striped belly, wings and beak all look like a House Finch. Weird little guy - like a punk finch.

Whilst trying to figure out what it is - I came up with House Finch, too - I read that the colour in Rosefinches comes from their diet. (So blf wasn't so far out after all. :-))
Assuming that's correct in this case, could it be a dietry problem?