The relation between urinary cortisol levels and social behaviour in captive timber wolves

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Abstract
The relation between involvement in aggressive interactions and a physiological index of stress was examined in a captive timber wolf pack (Canis lupus). Urine samples from known individuals were collected from snow throughout the mating season and analyzed for levels of the stress responsive hormone cortisol. When expressed relative to creatinine concentrations in the sample (thereby correcting for differences in urine concentration and dilution in snow), individual differences in urinary cortisol levels were found. These differences were consistent with behavioural data on aggression collected during the same period. Although males engaged in intrasexual aggression more frequently, female aggression was more serious in that females were more likely to be the targets of group chases and attacks. The dominant and only breeding female also aggressed against the two highest ranking males during courtship and mating contexts. The lowest ranking female had a significantly higher cortisol:creatinine (C:C) ratio than all other females, and the second-ranking (beta) and most aggressive male, whose social position was unstable, had significantly higher C:C ratios than most other males. The data also suggest that urinary C:C ratios increase during the mating season for at least some individuals and vary in response to acute social stressors. The C:C ratios presented are similar to those reported from the urine of domestic dogs and a small sample of wild wolves, suggesting that these data from captive animals are not unusual. Comparisons with literature on primates and potential applications of these techniques are briefly discussed.