Too warm to play: temperature selectively constrains social behaviour in the Alpine marmot, Marmota marmota

Abstract

Temperature is an important abiotic factor constraining animal physiology, yet its impact on social dynamics remains largely unexplored in wild endotherms. Here, we investigated the effect of temperature on social interactions of Alpine marmots, a cooperative breeder highly adapted to cold environments. We collected 667 social interactions during 189 h of observation of 14 family groups, combined with temperature records from June 2023, 2024 and 2025. We analysed these data using generalized linear mixed models to test thermal effects across four different social behaviours (i.e. play, agonistic, greeting and grooming). We found that temperature acts as a nonuniform constraint on sociality. While essential behaviours required for group stability (i.e. grooming, greeting and agonistic) were buffered against thermal stress, facultative behaviours (i.e. play) were suppressed. Specifically, play activity peaked at 12.8 °C and interactions/h collapsed to near zero as temperature rose above 21 °C. These results suggest that, in Alpine marmots, play may be the first social behaviour to decline under heat stress. Consistent with the surplus resource theory, play is a labile trait that occurs only in a ‘relaxed field’ and is prone to be sacrificed under stressful conditions. As play is essential for the acquisition of motor and social skills in immature individuals, its reduction may lead to long-term developmental deficits. With this study, we propose that the decline of play interactions may serve as an early bioindicator of thermal stress in Alpine marmot populations, highlighting how global warming can compromise social dynamics before affecting demographic parameters.