Ecological and Social Factors Affecting Hatchability of Eggs

Hatchability, defined as the proportion of eggs surviving to the end of incubation that hatch, varies among populations of birds.Here, I examine the effects of a variety of variables on hatchability in a comparative analysis of 155 studies of 113 species.Of the ecological and geographical variables considered, latitude, diet, and nest type explain a significant amount of the variance in hatchability due to a significant increase in hatchability along a latitudinal gradient and a decrease in hatchability in carnivorous and holenesting species compared to herbivorous and open-nesting species.Of the variables related to sociality, all affect hatchability adversely as they increase along a sociality gradient (defined as the likelihood of increasing frequency of interactions with conspecifics), significantly so in the case of social organization and possibly incubation pattern.In addition, hatchability of eggs in nests of Acorn Woodpecker (Melanerpes formicivorus) groups containing more than one breeding male and/or female is significantly lower than that observed in groups with a single breeding individual of each sex.Although the causes of these trends in hatchability are unclear, these results provide comparative evidence to support the hypothesis that there is a direct, detectable reproductive cost to individuals pursuing strategies that are more social.