Variation in the frequency of tool use across and within sea otter (Enhydra lutris) populations
Sea otters (Enhydra lutris) are well known and conspicuous tool users, but little is known about what drives the maintenance of this behavior in populations or individuals. I investigated how variation in the frequency of tool use across and within sea otter populations may be influenced by ecological factors such as age class, sex and reproductive status, geographic location, feeding habitat, and prey type. Additionally, I explored whether consistent inter-individual differences in tool use occurred and if the frequency of tool use occurrence was related to learned diet specializations. I used observed foraging and tool use data collected from nine sites across two subspecies of sea otters. Over 500 individuals were observed feeding and over 100,000 feeding dives were recorded between 1985 and 2011. Using binary generalized linear mixed effects models, I found the type of prey consumed the strongest predictor of the frequency of tool use across populations, although all factors contributed to the best fit model. In Monterey, California, I collected longitudinal data on sixty- three individuals for a minimum of one year. I found that individuals specializing in prey that required tools were more likely to carry-over this behavior to other prey consumed. My results suggest that the frequency of tool use in sea otter populations and individuals is influenced by ecological factors such as the consumption of prey that is difficult to access, and the "behavioral inertia" of individuals learning to use tools for particular prey items.