Patterns of Visually Observable Behaviour and Vocalizations in Groups of Female Sperm Whales

Abstract

[Hourly records of the visible activities and vocalizations of groups of female and immature sperm whales, Physeter macrocephalus, off the Galapagos Islands were used to investigate relationships between vocalizations and visible activities, and to examine patterns of behaviour. There were strong correlations between most recorded variables, and multivariate analysis showed the rates of performing visually observable activities and vocalizing to be largely represented by an axis which is termed Sociality. About three quarters of the time sperm whales engaged in relatively stereotyped foraging for food, diving regularly, moving steadily, appearing only briefly at the surface in small clusters, and making regularly spaced trains of 'usual' clicks. However, for periods which usually lasted either about one or about five hours, and often in the afternoon, the whales would aggregate at the surface, usually in large, slow-moving clusters, often making patterned series of clicks called 'codas'. There was considerable variation in the behaviour observed, and sounds heard, during these periods of Aggregation. The mean levels of Sociality did not vary significantly between years, with season or with a measure of feeding success. The results are consistent with the hypothesis that a primary function of these periods at the surface is the maintenance of social bonds, although other functions are not excluded., Hourly records of the visible activities and vocalizations of groups of female and immature sperm whales, Physeter macrocephalus, off the Galapagos Islands were used to investigate relationships between vocalizations and visible activities, and to examine patterns of behaviour. There were strong correlations between most recorded variables, and multivariate analysis showed the rates of performing visually observable activities and vocalizing to be largely represented by an axis which is termed Sociality. About three quarters of the time sperm whales engaged in relatively stereotyped foraging for food, diving regularly, moving steadily, appearing only briefly at the surface in small clusters, and making regularly spaced trains of 'usual' clicks. However, for periods which usually lasted either about one or about five hours, and often in the afternoon, the whales would aggregate at the surface, usually in large, slow-moving clusters, often making patterned series of clicks called 'codas'. There was considerable variation in the behaviour observed, and sounds heard, during these periods of Aggregation. The mean levels of Sociality did not vary significantly between years, with season or with a measure of feeding success. The results are consistent with the hypothesis that a primary function of these periods at the surface is the maintenance of social bonds, although other functions are not excluded.]