Comparing the Relative Effects of Year, Seasonality, Territory, and Individual on American Kestrel Carotenoid Concentrations /
Carotenoids are organic pigments manufactured by plants. Animal consumption of these pigments effects coloration, immune function, and capacity to respond to oxidative stress. Carotenoids have been found to be indicators of individual body condition, and therefore may contribute to survivorship in wild birds. American Kestrels’ expression of carotenoid concentration is found in areas such as the cere, tarsi, and feather coloration as well as circulating carotenoids in blood serum. We examined the factors that affect circulating carotenoids in American kestrels (Falco sparverius). We hypothesized that carotenoids may be predicted by year, season, individual, territory, gender, or a combination of these factors. We sampled 114 adult female and 99 adult male breeding American kestrels from April-June in 2008-2012. We used the variables year, date, territory vegetation, sex, and individual to predict carotenoid concentrations. Male kestrels had higher concentration of carotenoids than females, perhaps because of mobilization for sexually selected traits. We also found support for year and seasonal effects of carotenoids. Individual was a significant predictor of carotenoids with a vast amount of variation from individual to individual while territory did not explain much variation. This implies that individual birds differ in their ability to acquire carotenoids regardless of the vegetation surrounding their nesting area.