Meeting Abstract
48.8 Jan. 6 Share the warmth: Thermal benefits of huddling behavior in California sea lions (Zalophus californianus) MOSTMAN-LIWANAG, H.E.*; WILLIAMS, T.M.; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz mostman@biology.ucsc.edu
Otariids are highly communal pinnipeds that often congregate in large numbers on coastal rookeries. Although this behavior serves a social role, it also has the potential to change the microhabitat, and thus the local thermal conditions experienced by the animals. However, the thermal consequences of huddling in pinnipeds has neither been quantified nor tested despite a propensity for close proximity in some species. To investigate this, we quantified the huddling behavior of California sea lions by measuring the proximity of individuals from digital photographs, and determined the thermal microhabitat of huddles using infrared temperature monitors. All animals were measured on San Nicolas Island (California) for six days in winter (mean Tair=15.5°C) and summer (mean Tair=22.7°C). We found that sea lion huddling behavior increased in colder weather, as determined from three indices. First, a larger proportion (up to 97%) of the animals participated in huddles rather than resting alone during the winter season. Second, the number of animals per huddle was larger (reaching 172 animals) during the colder season. Lastly, sea lions participating in this behavior huddled more tightly (i.e. a greater proportion of skin surface area was in contact) in cold temperatures. The temperature differential between the animals� skin surface and that of the surrounding substrate was significantly greater (P<0.001) for huddling sea lions (6.0±3.6°C) than for animals resting alone (3.0±2.8°C). Furthermore, this differential was inversely proportional to ambient temperatures. These results suggest that huddling behavior in California sea lions provides a significant thermal benefit that likely shapes the social behavior on rookeries. Supported by the Alaska SeaLife Center.
