Variation in relative egg and yolk size in Tachycineta swallows: insights from a network spanning the Western Hemisphere

MARTÍN QUIROGA; FLORENCIA BULIT; VIVIANA MASSONI; DAN ARDIA; CAREN COOPER ; MELINA BARRIONUEVO; M. STRAGER; A. KARL; M. WALTERS; M. LILJESTHROM; M. SHULMAN; N. HAMM; M. FAST; R. CLARK ; D. WINKLER

Campos de Jordao

Congreso; XXV International Ornithological Congress; 2010

AQUAVIVA

The number and quality of eggs can strongly affect offspring fitness. However, there is no clear pattern in egg-related fitness tradeoffs across several bird taxa. Geographically, relatively larger eggs are generally found in the tropics and southern hemisphere relative to those in northern temperate zones. Egg size variation might be driven in part by variation in how females cope with downturns in ambient temperature and food availability which, as a consequence, might affect nest attentiveness. However, relative egg size alone may not accurately reflect the maternal investment in the egg, as only the yolk contains the energy that embryos need to grow. Here we describe patterns of egg and yolk size variation across a broad geographic gradient encompassing 11 study sites along an 8400 mile range in the Western Hemisphere from Alaska to Argentina. We developed standardized protocols to compare relative egg size (corrected for body mass), ambient temperature during egg development and food availability. In addition, we estimated yolk area using standardized digital-candlers (Ovoluxes). This approach allowed us to address the following questions: 1) Is there a relationship between number and quality of eggs within Tachycineta swallows? 2) How does parental investment in egg and yolk size vary geographically? 3) Does relative yolk size vary with latitude? 4) Is there variation in seasonal changes in egg and yolk size across sites? This work has been done within the Golondrinas de las Americas network (http://golondrinas.cornell.edu), which provides a distinctive opportunity to explore life history variation in relation to latitude and phylogeny. We will also discuss the challenges and rewards of international standardization and collaboration within this network.