Terrestrial Tree Hugging in a Primarily Arboreal Lemur ( Propithecus verreauxi ): a Cool Way to Deal with Heat?

High temperatures pose a significant risk to mammals, especially those living in hot and dry environments such as southern Madagascar, the location of Bezà Mahafaly Special Reserve (BMSR). At BMSR, we observed sifakas ( Propithecus verreauxi ) hugging tree trunks while resting on the ground during the mid-day heat of the late dry season. These highly arboreal lemurs are more vulnerable to predation on the ground. To explore whether tree hugging affords a thermal advantage, we collected 615.7 hours of behavioral data on sifakas in six groups, together with the temperature of the air, ground, and tree trunks used during hugging bouts. We observed hugging only when ambient temperatures were high (above 30°C), and mean daytime temperature had a significant positive effect on whether sifakas engaged in tree hugging on a given day. The surface at the base of hugged trees were significantly cooler (by ~3-5°C) than ambient air temperatures and surface temperatures further up the trunk, likely enabling animals to dissipate body heat. These data suggest that terrestrial tree hugging behavior contributes to thermoregulation in this lemur population and, coupled with evidence from koalas ( Phasocolarctos cinereus ), indicate that trees may provide a widespread thermal benefit for mammals facing heat stress. The capacity of sifakas to avoid heat stress will be critical to their persistence under predicted temperature increases in southern Madagascar over coming decades , and needs to be better understood in the context of long-term conservation planning.