Environmental correlates and effects of organochlorine pollutants on the physiological condition and carotenoid-based coloration of a South African avian predator

Abstract

Contaminants such as PCBs and DDTs have caused population declines in avian predators. Banned in the 70-80s, their use persists in some countries. In South Africa, PCBs were still used in electric transformers in 2010. DDT was also intensively (illegally) sprayed in agricultural areas until 1985 and is currently legally used in the northeast of the country for malaria control. Residues from former and current use of PCBs and DDT therefore likely persist in the environment. Understanding patterns of OC contamination can be crucial for the conservation of wild animals such as African raptors. The Black Harrier Circus maurus is an endangered raptor endemic to southern Africa. This bird breeds in indigenous vegetation of southwestern South Africa, where agriculture and urbanization have rapidly developed since the 50s. We collected blood samples from wild nestlings (n=90) and adults (n=23) in 2012-2014. PCBs and DDT were detected in 79% and 84% of sampled individuals, respectively. Nestlings had higher ΣPCB and p,p’-DDT levels than adults, which in contrast presented higher levels of p,p’-DDE than nestlings. ΣPCB Levels increased with an index of “electric transformer density”, which combined the number and power of electric transformers around active nests. Levels of p,p’-DDE increased with the % of wetlands within the breeding territory, suggesting bioaccumulation in sediments, and with the % of bird biomass in diet, confirming intra-specifically an association between diet and DDT contamination. Several indicators of physiological condition were affected in contaminated individuals: white blood cell count increased with higher p,p’-DDT levels and the heterophyl:lympocyte ratio increased with higher ΣPCB levels. In nestlings, ΣDDT levels reduced the amount of circulating carotenoids and the orangeness of colored integument developed by nestlings. Our results suggest that OCs can increase physiological stress and affect immunity, and may disrupt carotenoid-based signalling in exposed nestlings interfering with communication processes. OCs are therefore still a current cause of concern for threatened Black Harriers and other sympatric predators.