Friday, August 30, 2013

Luecistic Tree Swallow

While birding in Rice County on Wednesday, I found swallows beginning to flock on local power-lines. One of these birds, a Tree Swallow, sported a white cap reminiscent of a South American White-capped Dipper. Clearly this individual is aberrant, a leucistic bird. Partial leucism, like on this swallow, occurs when pigment production is blocked and the result is a bird with white and normal patches. Leucistic birds generally show normally colored eyes, whereas albinos have pink eyes. Also notice the white bands on the edges of this swallow’s scapulars.

Note this bird's frayed flight feathers. Perhaps more than leucism is affecting these feathers, resulting in weak feather structure. Although I have no evidence in this case, another possibility is that other Tree Swallows have been harassing this bird. Leucistic Barn Swallows are known to be attacked by their fellow flock members (Brown and Brown 1999). Swallows can be extremely aggressive. Tree Swallows are known to kill their “step children,” when a male mates with a recently “widowed” female (Winkler et al. 2011),

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