Wednesday, February 8, 2012

Photo Quiz solution and Aberrant Plumages in Birds

Admittedly, this was a difficult bird to identify to race given it's clearly aberrant plumage.  The patches of white on the back, nape, rump, above the eye and elsewhere (including a single greater covert) would make any bird challenging to identify.  The distinctly round head, thick legs, overall bulkiness, and long nails (hard to see, but they're there) make Fox Sparrow the obvious choice, and most people got this.  Race is more difficult. The bird's washed out breast and belly (either from bad lighting, leucism, or both), and the "albinistic" (we'll get into this later) patches of feathers greatly reduce the value of using plumage to identify race.  This bird is very long-tailed and has a rather thick bill.  The gray head may suggest Slate-colored, but doesn't rule out Thick-billed.  The brown spotty streaking on the breast and flanks also suggests Slate-colored (vs. the black spots on Thick-billed), but this is possibly/probably due to the aberrancy in plumage.  The flight feathers appear slightly reddish, but not as reddish as typical Slate-coloreds.  Wing bars are completely absent.  The extreme length of this bird's tail and thickness of the bill rules out Sooty and Red Fox Sparrows which are short-tailed.  Slate-colored would be a lot more likely in Marin county, but the bill on this bird is simply too heavy for that race.  This bird probably represents Passerella iliaca brevicauda, which is smaller billed than the massive-billed P. s. megarhyncha.

Another part of the quiz, though, was determining what was causing this bird to look so odd.  So far I've used the terms albinistic and leucistic.  Albinism is the absence of melanin anywhere in a bird, so an all white bird (although sometimes with some color from pigment other than melanin) and red/pink eyes is always called albinistic.  For the purposes of this quiz, I accepted the terms leucistic, partially leucistic, and partially albino since these terms are often used to mean the same things.  However, it is important to point out the differences in these terms, and why certain terms are less accurate.  Since partial albinism means partial complete absence of pigment, it makes little sense, and is generally not used as frequently anymore.  However it used to be used quite frequently to describe the pied appearance as is seen in this bird.

Leucism generally describes two phenomena, a pied/piebald patterning (patches of feathers/skin with no pigment (i.e. they are white patches) as in this bird, or an overall reduction of pigment evenly over the entire bird giving the bird a faded appearance.  One of the players on this quiz pointed out that he does not like the term leucistic since it describes multiple problems.  Still, both phenomena termed leucistic stem from the same problem - a pathology that causes melanin and other pigments to be deposited aberrantly. This is opposed to albinism, which means the bird presumably cannot make melanin at all.  This bird has pigment, but also appears to be faded in some parts, and yet completely white in others.  I would call this bird leucistic, but if anyone still believes otherwise, I encourage you to comment on this post.

Conor Higgins
Rich Stallcup
Nate Fronk

Thanks for playing!
~Luke Musher

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