Habitat use of culturally distinct Galápagos sperm whale Physeter macrocephalus clans

Abstract

Ecological niche is traditionally defined at the species level, but individual niches can vary considerably within species. Research on intra-specific niche variation has been focussed on intrinsic drivers. However, differential transmission of socially learned behaviours can also lead to intra-specific niche variation. In sperm whales Physeter macrocephalus, social transmission of information is thought to generate culturally distinct clans, which at times occur sympatrically. Clans have distinct dialects, foraging success rates, and movement patterns, but whether the niches of clan members are also different remains unknown. We evaluated the differences in habitat use of clans off the Galápagos Islands, using data collected over 63 encounters between 1985 and 2014. During encounters, we recorded geographic positions, determined clan identity through analysis of group vocalizations and individual associations, and used topographical and oceanographic variables as proxies of sperm whale prey distribution. We used logistic generalized additive models, fitted with generalized estimating equations to account for spatiotemporal autocorrelation, to predict clan identity as a function of the environment descriptors. Oceanographic variables marginally contributed to differentiating clans. Clan identity could be predicted almost entirely based on geographic location. This fine-scale, within-region spatial partitioning likely derives from whales preferring areas where members of their clans occur over temporal scales of a few months to a few years. By identifying differences in clans’ space use, we have uncovered another level of sperm whale life that is likely influenced by their cultural nature.