Physiological stress in wild and captive Cantabrian capercaillies (Tetrao urogallus cantabricus): temporal trends and methodological implications

Abstract

Determining the environmental factors that may explain the variation in physiological stress is crucial in threatened species since they can influence mortality and therefore population viability. Here we studied the climatic factors that can be associated with corticosterone levels in feathers, as proxy of physiological stress, in Cantabrian capercaillies (Tetrao urogallus cantabricus). We used feathers collected both from individuals in captivity and in wild conditions. Samples from wild birds were collected from 1998 to 2017 and 35 climatic variables (temperature and precipitation) were considered. Analyses of repeatability showed that body and secondary feathers had a highly repeatable corticosterone levels within individuals. By using only body and secondary feathers, captive birds had lower corticosterone levels and that stress levels increased overtime but stabilized in the last few years. None of the climatic variables were related to corticosterone levels. We speculate that the observed temporal trend in stress levels might reflect access to specific food, but that such limitation can be tightly linked to other temporal changes like structure or habitat composition or interactions with other competing species for this food resource. If food limitation is a factor explaining high stress levels, it can be a plausible explanation for the lower corticosterone levels observed in captive birds compared to wild animals. From a methodological perspective, those feathers from the same individual particularly body or secondary ones, regardless of the sex, should be selected to implement a continuous monitoring of physiological stress in wild or captive capercaillies.