The importance of intrinsic traits, environment and human activities in modulating stress levels in a wild ungulate

Identifying the ecological and anthropogenic processes that affect wildlife physiology, and that may operate as chronic stressors, is of prime importance to implementing appropriate management and conservation strategies. Although advances have been made in understanding the physiological ecology of wild ungulates, little is known of how multiple intrinsic and ecological factors work, either independently or synergistically, to modulate their stress responses. By using faecal glucocorticoid metabolites (FGM) as indicators of stress, a set of environmental and human determinants affecting the stress physiology of wild red deer (Cervus elaphus) was examined in the Mediterranean ecosystems of south-western Europe, where this species is subjected to contrasting weather regimes and hunting management systems. Variation-partitioning techniques were also used to estimate the comparative influence of factors related to an individual's intrinsic characteristics, environmental conditions and management practices in shaping physiological stress levels. Our results showed that factors related to hunting management were the main drivers of FGM variation in red deer, followed by those related to the environmental conditions and individuals' traits, and their effects were closely associated to spatio-temporal variability. Holding massive hunting events involving the use of hounds, as well as high population densities, were related to more long-term stress levels in the populations studied. Evidence was also found that supplementary feeding practices may mitigate the negative effects of reduced food availability in overabundant deer populations. Weather conditions were also significant factors explaining variation in stress levels; accumulated rainfall and an increase in ambient temperatures during the coldest months were associated with a decrease in stress hormone levels. No differences in hormonal concentrations were found between males and females, but higher levels of hormone metabolites were detected in younger animals in both sexes. Our findings provide an integrated perspective of how multiple factors impact on stress physiology in large wild herbivores and highlight the importance of considering management practices, as well as spatio-temporal variation, when assessing stress-inducing factors in wild populations. Given the implications of this study regarding the impact of human activities on physiological stress levels in wild animals, it could be an important basis to support wildlife management decisions.