The Function And Early Ontogeny Of Individual Variation In Conspicuous Begging Behavior In A Passerine Bird

Abstract

Increasingly, individual variation is being recognized as an important influence on behavioral evolution. Sources of variation are therefore an important target for research into the development, evolution, and function of behavior. By providing information about the timescale on which individuals are responsive to their environment, patterns of within-individual variation can shed light on function of behavioral variation. Here, I wanted to understand the function of behavioral variation and the genetic and environmental sources of variation in behavior. First, I test the hypotheses that variation in begging signals nestling hunger, need, or quality. Hunger is a short-term response to food deprivation, while need and quality give long-term information about fitness benefits of gaining more food and fitness potential, respectively. Second, I test the hypotheses that variation in begging is due to genetic, permanent environment, common environmental, and maternal effects. I test these hypotheses in the begging behavior of western bluebirds (Sialia mexicana), making repeated measurements across the nestling period. I show that begging behavior is consistent across the nestling period, and that nestling begging intensity increases with food deprivation. Nestlings fed during a given parental visit beg at higher intensity than nestmates, and on average wait longer since their last meal compared to individuals who were not fed in the same visit. These results support the hypothesis that variation in nestling begging signals hunger. I also show that responsiveness to food deprivation is negatively related to condition, but this effect is not consistent across the nestling period. Finally, variation in begging is produced by a common environmental effect that is correlated through time, suggesting that begging is strongly influenced by the nest environment. Together, these results indicate that variation in begging signals short-term changes in hunger and that environmental effects dominate the production of variation in begging.