A puff of air on the belly of a Barn Swallow reveals an incubation patch. |
Development of these brood patches is prompted by rising levels of hormones. They form in whichever sex cares for the eggs and young, usually females but often males as well. The skin swells and the blood vessels feeding the skin expand.
The bare patch is revealed when a bird settles in to the nest, spreads apart their contour feathers that remain over the patch, so that bare skin rests directly on the eggs. This contact transfers body heat to incubate the eggs and chicks.
The bare patch is revealed when a bird settles in to the nest, spreads apart their contour feathers that remain over the patch, so that bare skin rests directly on the eggs. This contact transfers body heat to incubate the eggs and chicks.
Later the lost feathers are replaced in the complete molt following the breeding season.
Source and photo credit to: Avian Reproduction: Clutch Size, Incubation, & Hatching - http://people.eku.edu/ritchisong/avianreproduction2.html
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Bird Basics
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