Environmental determinants of chronic stress in fallow deer

It remains unclear how animals are affected by different environmental stressors, including climatic, anthropogenic and conspecific interactions. Assessing seasonal changes in hair cortisol concentration (HCC) in fallow deer from 10 populations across England, we found a negative correlation with precipitation in May-June and with average temperature in late winter (January-February). There was a positive correlation with precipitation in November-March and the number of days of airfrost, two measures which would also reflect increased environmental challenge over winter. While the same climatic factors appeared to influence HCC of both sexes, the primary social factor affecting HCC in females was the level of competition experienced for quality food resources. By contrast, the major factor affecting HCC in males was the proportion of males within the population overall, perhaps reflecting the degree of male-male competition.