Friday, April 22, 2011

Breeding Siskin

Erika took this photo while I gently blew on this Pine Siskin's breast and belly.  Lacking a cloacal protuberance, this siskin is female. The bird has an obvious and well-developed brood patch.  In most passerines, only the females develop brood patches. Beginning birders are sometimes surprised that birds' feathers grow in tracts, not all over their bodies.  Breeding birds lose the few pinfeathers that sometimes grow between the tracts and the naked skin becomes highly vascularized.  The result is a brood patch, which birds use to incubate their eggs.  Breeding bird surveyors cite brood patches as physiological evidence of breeding.  This record is a good one for southeastern Minnesota.  Siskins do not breed here every year, usually only after invasion years.  Siskins are early breeders--this photo was taken on 21 April 2011 in Northfield. This bird, banded and released unharmed, is the second breeding siskin of the 2011 spring.

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