Resource allocation across America: variation in relative egg and yolk size in Tachycineta swallows

QUIROGA, M.; BARRIONUEVO, M.; BULIT, F.; ARDIA, D.; WINKLER, D.

Cornell University, Ithaca, NY, USA

Congreso; XII ISBE Internacional Behavioral Ecology Congress; 2008

International Society for Behavioral Ecology

Variation in egg size and composition can have important consequences for the quality of offspring, as egg size can influence hatching success and offspring size and condition. Egg size is influenced by different factors, such as food availability, individual quality and different allocation trade-offs. Egg size alone does not reflect parental investment, as yolk mass is the energy reserve that embryos use to develop. Swallows (Tachycineta) are secondary cavity nesters that use nest boxes to breed, and they are distributed throughout the Americas. The Golondrinas de las Americas network (http://golondrinas.cornell.edu), a group of biologists studying Tachycineta swallows from Alaska to Argentina, provides a unique opportunity to study yolk resource allocation in different Tachycineta species at different latitudes. We developed an update of a nondestructive technique (ovolux) to estimate yolk mass via standardized digital-candler photographs. We measured yolk mass and egg size in different study sites over an 8400 mile range in the Western Hemisphere: Alaska, Massachusetts, New York, Tennessee, Pennsylvania, California, Argentina . We test the following questions:  1) Does the relationship between egg size and yolk mass vary with latitude? 2) Is the seasonal decline in yolk mass similar across sites? 3) Does investment in yolk mass differ with clutch size? 4) Do different species within the genus vary in parental investment in egg and yolk?