Social organization of sperm whales off the Galapagos Islands, February-April 1985.

Female and immature Physeter macrocephalus were clustered into 13 groups with closed membership during the study period. These groups had a median estimated population of 19.5 animals each, and associated with one another at different times. The groups showed no significant immigration into or emigration from the study area. Seven large males were identified. These associated with each other and the groups of femals and immatures for periods lasting c6 h. Individual males were found with different groups of females and immatures at different times. A simple model suggests that a male employing a 'searching' strategy should encounter more oestrous females than the traditionally accepted 'harem' holder when the interval beween encountering groups of females is less than the duration of the females' oestrus. Neither the groups of females nor the mature males appeared to possess territories or preferred ranges.-from Authors