Tool-Using Behavior of the California Sea Otter

During 6 days of observations at the Point Lobos State Park in California, a total of 30 separate instances of tool using by sea otters (Enhydra lutris) was observed, and the times and frequencies of several aspects of the behavior were quantified. Otters opened mussels by pounding them repeatedly against a stone lying on the chest, but on occasion such other items as crabs and urchins were also pounded, either against a stone or on the chest itself. The mean number of blows necessary to open a mussel was 35.5 (range 6–88, sd 20.4). The same stone was frequently retained for several successive food items, and such retention would seem to imply an anticipation of use that goes beyond the immediate situation. The tendency of otters to manipulate and to pound is far from stereotyped in its application and seems to provide the basis for learning the use of tools in feeding behavior.