Heat stress conditions affect the social network structure of free-ranging sheep

Extreme weather conditions, like heatwave events, are becoming more frequent with climate change. Animals often modify their behaviour to cope with environmental changes and extremes. If the environmental conditions influence the trade-off between an individual's social propensity and optimal thermoregulation through shade use for instance, then divergent social decisions may be made. Hence, such behavioural changes have the potential to influence an individual's position in its social network, and the social network structure as a whole. We investigated whether heat stress conditions (quantified through the Temperature Humidity Index) and the resulting use of shaded areas, influences the social network structure and an individual's position in it. We studied this in free-ranging sheep in the arid zone of Australia, GPS-tracking all 48 individuals in a flock. When heat stress conditions worsened, individuals spent more time in the shade and the network was more connected (higher density) and less modular. Furthermore, an individual's social connectivity scaled with its shade use behaviour. Interestingly, individuals with intermediate shade use were most strongly connected (degree, strength, betweeness), indicating their importance for the connectivity of the social network during heat stress conditions. Our study shows that heat stress conditions, which are predicted to increase in severity and frequency due to climate change, influence the resource use within the ecological environment. This has flow on effects for the animal's social environment through the changed social network structure.