Carotenoid-based coloration, diet and healthiness in nestlings of a threatened and endemic Southern African raptor, the Black Harrier

Resumen del trabajo presentado a la VI North American Ornithological Conference (NAOC): Bringing Science and Conservation Together, celebrada en Washington DC (USA) del a6 al 20 de agosto de 2016.The Black Harrier is an endemic raptor to southwestern Africa, considered as regionally Endangered. The reasons for its scarcity remain poorly known. In this context, it is useful to assess the health status of the population to better understand potential limitations and threats. Carotenoid-based ornaments displayed by many birds have been proposed to reliably indicate an individual´s condition and health status: carotenoids (acquired through diet) may be allocated to increased coloration, or mobilized to specific uses such as self-maintenance. Here, we evaluate to what extent carotenoidbased coloration of nestlings (yellowness of cere and tarsus) could be used as an indicator of health. We show that both carotenoid-based coloration and circulating carotenoids (blood plasma) increased with age (p < 0.0001, p=0.021, respectively), and when diet included increasing proportion of birds versus rodents (p=0.030, p < 0.0001, respectively), but not when nestlings were in better condition (weight relative to age). This suggested that carotenoid availability reflected the quality of ingested food rather than quantity. Most importantly, we found that nestlings eating more birds also had greater levels of DDTs, and that the circulating carotenoid levels were negatively associated with DDT levels (p=0.004). No effects of PCBs or DDTs were found on coloration. Our results suggest that diet quality strongly influence carotenoid availability as well as pesticide (DDTs) intake. Nestlings feeding primarily on rodents, the species’ main prey, were less exposed but more carotenoid-limited. We discuss the broader implications of these results for the health assessment and conservation of the Black Harrier population.Peer Reviewe