Variation in avian egg size and the consequences for offspring fitness

Abstract

In oviparous species such as birds, the investment in egg size is thought to represent a strong mechanism through which maternal effects can influence components of offspring fitness. Within several avian species egg size varies significantly and is often positively correlated with hatchling phenotype, growth and survival. However, there is little direct evidence for strong positive effects of egg size on offspring quality. This review aims to evaluate the current understanding of the effects of egg size on offspring fitness and assess the factors which confound many of the studies investigating egg size effects. It is concluded that despite extensive research, the exact relationship between avian egg size and offspring fitness remains undefined. Identifying egg size as the causal driver of changes in offspring quality continues to be a problem in all studies. Thus, in order to establish the effect of egg size per se, further studies are required which successfully control for potentially confounding variables which may obscure current results.