Social organization in northern bottlenose whales, Hyperoodon ampullatus: not driven by deep-water foraging?

It is postulated that deep-water foraging in sperm whales, Physeter macroce phalus, has led to communal care of young and long-term female bonds. By st udying the social organization of a second, unrelated, deep-diving species, the northern bottlenose whale, we investigated the role that deep diving m ay play in the evolution of cetacean sociality. Northern bottlenose whales in a deep-water canyon, the Gully off Nova Scotia, Canada, form small group s ((X) over bar +/- SD = 3.04 +/- 1.86). Associations within age/sex classe s (female/immature, subadult male and mature male) were significantly highe r than associations between different classes. Females and immature bottlen ose whales formed a loose network of associations, showing no preferential associations with particular individuals or those from specific age/sex cla sses nor any long-term bonds. Mature and subadult males had stronger associ ations with individuals in their own class, and associations between some m ales lasted for several years, although males also formed many short-term a ssociations. Overall the social organization of northern bottlenose whales in the Gully appears to resemble that of some bottlenose dolphins, Tursiops truncatus, living in shallow, enclosed bays. Thus deep-water foraging does not appear to necessarily lead to the evolution of long-term bonds between females., (C) 2001 The Association for the Study of Animal Behaviour.