Personality differences are related to long-term stress reactivity in a population of wild eastern chipmunks, Tamias striatus

Consistent individual behavioural differences in exploration, docility and boldness are often correlated and are associated with differences in short-term neurophysiological responses to environmental perturbations in many animal species. These physiological mechanisms are much less studied over longer periods in wild populations. Here we report the relationships among exploration, docility measured in open-field tests and trappability, taken as an index of boldness, in a wild population of eastern chipmunks and investigate whether behavioural differences among individuals are associated with differences in autonomic nervous system reactivity. We also assess the cortisol level of individuals over several months to investigate whether chipmunks with different exploration levels display different mean cortisol levels or differences in their cortisol variability. Open-field tests showed consistent individual differences in exploration patterns (ranging from fast to slow). Faster explorers were less docile when handled and were trapped more often (males) or farther from their burrows (females) than slower explorers. Fast explorers also showed a higher sympathetic activity under restraint but more stable cortisol levels over the course of the active season, suggesting a lower hypothalamo–pituitary–adrenal reactivity. Our results show that chipmunks display individual behavioural variation and that these differences may have physiological implications over long periods in natural settings. Future studies should investigate the fitness consequences of such behavioural/physiological differences.

► Open-field tests showed consistent individual differences in exploration pattern, vigilance and centrality of chipmunks.
► Faster explorers were less docile and bolder and showed higher sympathetic autonomous system reactivity under restraint.
► Faecal cortisol levels over 5 months were not repeatable and not strongly related to behaviour in the open field.
► Faster explorers displayed less variable faecal cortisol levels over 5 months.