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Egg Coloration and Recognition of Conspecific Brood Parasitism in Eastern Bluebirds

Authors


Lynn Siefferman, Department of Biological Sciences, 331 Funchess Hall, Auburn University, AL 36849, USA.
E-mail: siefflm@auburn.edu

Abstract

Individual eastern bluebird (Sialia sialis) females produce clutches of eggs with unique coloration and older females and females in better body condition lay more pigmented blue-green eggs. Conspecific brood parasitism in this species is not uncommon and bluebirds occasionally reject what appear to be normal eggs by moving them to the periphery of the nest. I used UV-visual reflectance spectrometry to objectively measure coloration of eggs and nest material. To estimate the conspicuousness of the trait, I calculated the contrast between eggs and background nest material. I found high achromatic and chromatic contrast between the coloration of eggs and of the nests, suggesting that bluebird eggs are highly conspicuous. To test the hypothesis that expression of blue-green coloration eggs facilitates recognition of eggs laid by conspecific brood parasites, I cross-fostered individual eggs into host nests during egg laying and monitored the fate of those eggs. I found no support, however, for the hypothesis that egg coloration facilitates discrimination of parasitic eggs from host eggs.

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