UC Davis

Individuals within a species or population vary considerably in morphology and behavior. For many species, the specific drivers of variation in these phenotypic traits and their influence on individual fitness are poorly known. In this study, we hatched and reared wood ducks (Aix sponsa) in a captive common garden environment and then released them into the wild shortly after fledging age. For each individual, we evaluated metrics of size, growth, and behavior across ontogeny to determine whether individuals vary in morphological and behavioral traits when raised in a controlled captive setting. These individuals (n = 106 females) were then released into wild study populations where we tracked first year survival and multiple longer-term measures of fitness through standard monitoring methods and radio frequency identification. Using multivariate statistics and generalized linear models, we analyzed early life variation in morphology and behavior and their influence on individual fitness. Despite identical rearing conditions, we found considerable inter-individual variation in both morphological and behavioral traits. Additionally, we found correlations among egg size, hatch size, and fledging size, although maximum growth rate was the strongest predictor of fledging size. Contrary to evidence in the literature, we found no indication that morphological traits had any influence on first year survival; however, there was some evidence that survival was positively influenced by tonic alertness. We found evidence that both morphology and behavior were influential in multiple measures of long-term success. Here, our strongest results showed a negative relationship between initial size and longevity, and a positive relationship between tonic alertness and number of years incubating. The results of this study shed new light on the development of phenotypic variation in precocial birds and its consequences for individual fitness, and provides insight for captive breeding programs and conservation efforts.