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Familiarity between members of the same group is predicted to play a role in many biological processes. Familiarity can facilitate recognition, aggregation, communication, coordination and cooperation between group members. We tested a path of interrelated hypotheses on the effect of familiarity on survival, resource acquisition, predator avoidance and cooperation. We predicted that individuals with familiar members in their group would have a higher survival, acquire resources faster, avoid predators more easily and perform more cooperative actions. We used data from an online video game (Dead by Daylight) where small groups of four players (i.e. prey) must exploit resource patches while avoiding a predator. Prey can help fellow prey when the predator catches them (cooperation). Using a video game as a study system provided access to a large behavioural data set that would otherwise be difficult to obtain in nature. Using path analysis, we found evidence that coordinated resource acquisition and helping behaviours increased with the number of familiar individuals in the group. However, more cooperative actions increased their encounters with the predator and thus reduced their survival. When accounting for all indirect effects of familiarity on survival (through resource acquisition, cooperation and predator–prey encounters), familiarity had a small indirect net positive effect on survival.

• We examine the relation between individual behavioural variation and anthropogenic contaminants (ACs).

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.

The open-field test, which measures animal activity or distance covered by individuals subjected to a novel arena, is used frequently in behaviour studies. Studies generally report consistent individual differences in activity level in the open-field, but no study has tested whether individuals change their activity level differently within a single open-field test. If such differences exist, then the reliability of activity levels measured over the whole test may be affected by the duration of the test. Here, we present analyses showing how a reaction norm approach can be used to account for individual differences in temporal activity patterns. Specifically, we measured individual temporal patterns of activity in wild eastern chipmunks, Tamias striatus, and house mouse, Mus musculus, strains by decomposing the total duration of open-field tests into successive shorter time intervals. Open-field tests on chipmunks and mice lasted 3 min and 5 min, respectively. We detected repeatable individual and strain differences in temporal activity patterns. Activity during the first time interval (at the beginning of the test) was positively correlated with activity measured over the whole test, meaning that short tests yield a valid measure of activity in chipmunks and mice. We recommend analysing open-field data using random regressions to obtain activity measurements that are robust against differences in temporal activity patterns.