Egg Coloration and Recognition of Conspecific Brood Parasitism in Eastern Bluebirds


Lynn Siefferman, Department of Biological Sciences, 331 Funchess Hall, Auburn University, AL 36849, USA.


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.