Glance toward San Francisco's Pier 39, and you can spot one of the Pacific Ocean's great huddlers: the California sea lion. These aquatic mammals will spend hours on the planks in noisy piles, but they haven't gathered simply to bark and grunt at tourists. Sea lions group together to stay warm, according to a recent report in the Journal of Zoology.
The scientists took sea lions' temperatures with an infrared thermometer as the animals sat together or alone. Huddled sea lions, the biologists found, are significantly warmer than their solitary counterparts. And in the winter, sea lions pack together in larger, tighter groups.
Huddling may be more important for sea lions than other aquatic mammals, the study authors say, because sea lion fur is comparatively sparse. In seals, for example, a thick layer of fur protects the animals' skin from water, whereas water can seep through the sea lions' coats. This might explain the sea lions' aversion to spending time alone out of water -- even where there's not much space.
