Seasonal Carotenoid Variation in American Kestrels

Carotenoids are micronutrient pigments produced by plants that may convey immunological benefits to consumers. Animals with high levels of carotenoid intake may have improved health and higher survival. American Kestrels (Falco sparverius) from broods hatched early in the breeding season are more likely to survive and return to the breeding population than birds hatched later in the season. We hypothesized that breeding adults and nestlings may be affected by seasonal patterns in primary productivity that lead to changes in prey quality and availability; therefore affecting carotenoid intake. We collected blood samples from American Kestrels breeding in nestboxes south of Boise, Idaho and measured carotenoid concentrations via spectrophotometry. Our results supported our hypothesis that there are seasonal patterns in carotenoid availability, but trends did not match our predictions. Adult birds did show seasonal declines in carotenoids, while nestlings showed seasonal increases. Further, adult carotenoid levels did not predict nestling levels and there was high annual variation in carotenoid concentrations. Circulating carotenoids may be affected by factors other than food intake (i.e., hormones) making trend difficult to interpret

Plasma Carotenoid Concentrations of Incubating American Kestrels (\u3cem\u3eFalco sparverius\u3c/em\u3e) Show Annual, Seasonal, and Individual Variation and Explain Reproductive Outcome

In wild birds, the proximate and ultimate factors that affect circulating carotenoid concentrations remain poorly understood. We studied variation in plasma carotenoid concentrations across several scales: annual, seasonal, pair, territory and individual, and evaluated whether plasma carotenoid concentrations explained reproductive outcome of wild American kestrels (Falco sparverius). We sampled plasma carotenoid concentrations of 99 female and 80 male incubating kestrels from April to June in 2008 to 2012. Plasma carotenoid concentrations were explained by an interaction between year and sex, date, and random effects for pair and individual identity. In general, plasma carotenoid concentrations of males were significantly higher than females, but this depended on year. Within a breeding season, earlier nesting kestrels had higher carotenoid concentrations than later nesting kestrels, a pattern that is coincident with seasonal trends in local fitness. Pair and individual identity explained variation in carotenoid concentrations suggesting that carotenoid concentrations of mated birds were correlated, and some individuals consistently maintained higher carotenoid levels than others. Male carotenoid concentrations were positively associated with number of young fledged per pair. These results are consistent with the hypothesis that higher quality individuals have higher carotenoid levels compared to lower quality individuals, despite annual variations in carotenoid availability

Data from: Plasma carotenoid concentrations of incubating American kestrels (Falco sparverius) show annual, seasonal, and individual variation and explain reproductive outcome

In wild birds, the proximate and ultimate factors that affect circulating carotenoid concentrations remain poorly understood. We studied variation in plasma carotenoid concentrations across several scales: annual, seasonal, pair, territory and individual, and evaluated whether plasma carotenoid concentrations explained reproductive outcome of wild American kestrels (Falco sparverius). We sampled plasma carotenoid concentrations of 99 female and 80 male incubating kestrels from April to June in 2008 to 2012. Plasma carotenoid concentrations were explained by an interaction between year and sex, date, and random effects for pair and individual identity. In general, plasma carotenoid concentrations of males were significantly higher than females, but this depended on year. Within a breeding season, earlier nesting kestrels had higher carotenoid concentrations than later nesting kestrels, a pattern that is coincident with seasonal trends in local fitness. Pair and individual identity explained variation in carotenoid concentrations suggesting that carotenoid concentrations of mated birds were correlated, and some individuals consistently maintained higher carotenoid levels than others. Male carotenoid concentrations were positively associated with number of young fledged per pair. These results are consistent with the hypothesis that higher quality individuals have higher carotenoid levels compared to lower quality individuals, despite annual variations in carotenoid availability