Sociality helps mitigate anthropogenic risks: Evidence from elk crossing a major highway

Phenotypic variation among individuals scales up when they associate with others, creating variation within and among groups that can shape group-level outcomes such as when and where groups move. While sociality is thought to be a fitness-rewarding behaviour, empirical evidence supporting how it influences individual behaviour and the resulting fitness consequences (e.g. risk experienced) remains limited, especially in the context of human-modified landscapes. Here, we use empirical observations to test whether sociality helps animals cross busy roads. Our data came from free-ranging elk in a population where >75% of the adults were tracked, and in which group size and composition were highly variable. We combined field observations with GPS collar data to quantify four social phenotypes of individuals and groups: dominance (initiation of successful agonistic interactions), social connectedness (number and importance of social connections), social familiarity (frequency of association with group members in the past) and social stability (time since fusion with group members). We then investigated how these four social phenotypes influenced an individual's probability of crossing a major highway and tested if particular social phenotypes made better road crossing decisions (i.e. crossed at lower traffic volume). We found that who is in a group shapes the behaviour of group members around anthropogenic risks. Individuals in groups that were more dominant, more connected, and, to a lesser extent, more familiar had a lower probability of crossing the highway. Individuals that had spent more time with group members had a higher probability of crossing the highway. Importantly, our results suggest that sociality plays a role in safe movements around anthropogenic risks. Individuals in highly connected and familiar groups were less likely to cross the highway at high traffic volumes. Our work provides empirical evidence that sociality influences the movements of group-living individuals through anthropogenic disturbances and helps individuals mitigate the risks associated with such disturbances. Developing a comprehensive understanding of animal sociality in human-modified landscapes is especially important as social behaviours are simultaneously threatened by human disturbances, which could be particularly detrimental for group-living species if those same behaviours help individuals mitigate risks.