Behavioural thermoregulation in the Australian fur seal (Arctocephalus pusillus doriferus)

Physiological and behavioural adaptations shape an animal's thermoregulatory capacity. Pinnipeds - true seals (phocids), eared seals (otariids, including fur seals and sea lions), and walruses (Odobenids) - must thermoregulate in both aquatic and terrestrial environments. Fur seals are unique, relying on dense, water-repellent fur and moderate blubber for insulation, while true seals, sea lions, and walruses have lower fur densities and thicker blubber. Fur traps air when wet to reduce heat loss at sea, but its insulating properties when dry on land, along with those of furless flippers, remain unclear for fur seals. This study used behavioural observations and infrared thermography to examine posture and surface temperature of dry, hauled out adult female Australian fur seals (Arctocephalus pusillus doriferus) across a range of air temperatures (T_a). At T_a < 22 °C, huddling minimised heat loss by shielding flippers, and as T_a increased, seals shifted postures - Prone, Curled, Oblique, and Spread - to expose flippers and promote heat dissipation. Generally, flippers had a higher surface temperature than dry fur, however, at 26.5 °C, the fur surface temperature exceeded that of the flipper, with the fur appearing to insulate to retain heat beyond the flippers' dissipation capacity. At T_a > 30 °C, seals entered the water. With rising T_a predicted across this species' range, seals will likely spend more time in the water to overcome heat loss challenges. This shift could increase predation risk, energy demands, and negatively impact maternal investment.