Click rates from sperm whales

The rate of production of clicks by groups of (mainly female) sperm whales off the Galapagos Islands was dependent on two principal factors: the number of whales present and the behavioral state of the group. When the whales were in their principal (occupying about 80% of their time) behavioral state, diving deep for prolonged periods and usually being seen at the surface singly or in pairs, each whale made trains of clicks with an interclick interval of about 0.5 s about 70% of the time. About 10% of the time, the groups remained at or near the surface, with individual members forming clusters containing greater than five individuals, and being generally silent. Group behavior was sometimes intermediate between these extremes, with some whales silent at the surface in medium-sized clusters, and others clicking at depth. Click rate can be used as an indicator of the behavior of sperm whales, the size of a group, and/or the number of groups present. In our studies, groups associated often, and more frequently in 1985 than in 1987, perhaps because of changes in oceanographic conditions. The overall click rate, needed to calibrate acoustic censuses, was estimated to be 1.22 clicks s/ animal.