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

Abstract

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 individuals 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 individuals 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 individuals 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 individuals 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 animals social environment through the changed social network structure. Significance statementDue to climate change, animals experience heat stress conditions more frequently. When ambient temperatures are high, individuals can seek shaded areas to mitigate the effect. However, whether these behavioural changes affect the interaction patterns in social species is not well understood. We tracked all individuals in a flock of sheep using GPS collars. We demonstrate that when heat stress conditions worsened (higher temperature humidity index), individuals spent more time in the shade and the social network was more connected with less internal structure. Furthermore, an individuals social connectivity scaled with its shade use behaviour, and individuals with intermediate shade use were most strongly connected in their social network. Our findings illustrate that individuals respond to climate change induced environmental conditions and that this has flow on effects for their social connectivity and the social network of the group.