STRUCTURAL ASPECTS OF DOLPHIN SOCIETIES (POPULATION, SPINNER, SOCIAL BEHAVIOR, REPRODUCTIVE HORMONES, BOTTLENOSE, FLORIDA, HAWAII)

Though the social interactions of captive dolphins have been studied extensively, little is known about the structure or structural determinants of dolphin societies in nature. I examined 3 aspects of the structure of dolphin societies: (1) the population structure of free-ranging bottlenose dolphins (Tursiops truncatus), (2) the patterns of composition of social units of free-ranging bottlenose dolphins, and (3) the role of sexual behavior in social interactions between captive Hawaiian spinner dolphins (Stenella longirostris).; The bottlenose dolphin field studies were conducted along the central west coast of Florida as part of an ongoing study begun in 1970. Photographic identification, capture, sample, mark, and release operations, and behavioral observations from small boats were used to determine dolphin ranges and social patterns during 1980-1984. Behavioral interactions in a spinner dolphin colony at Sea Life Park, Hawaii, were examined during 1979-1981 relative to reproductive hormone concentrations of the colony members.; A resident community of about 100 bottlenose dolphins was identified. Socially, this community was relatively discrete from similar adjacent units. Within the community, schools were organized on the basis of sex, age, familial relationships, and reproductive condition. Females showed strong site fidelity; some individuals were seen in the area over more than 15 years. Different female groups used different core areas. Calves remained with their mothers for 3 years or more, before joining schools of subadults. At least some females were recruited back into their natal groups upon reaching sexual maturity. At least three generations of related females were recorded from local groups. Several males remained within their natal community upon reaching sexual maturity. Adult males mostly remained within the community range, traveling as individuals or pairs from one female school to another. However, males occasionally left the community for up to several months, suggesting a mechanism for genetic exchange between communities. A promiscuous mating system was hypothesized.; In the captive spinner dolphin colony, the amount of time spent in heterosexual swimming associations did not vary predictably relative to reproductive hormone levels. However, several classes of sexual behaviors occurred significantly more frequently when hormone levels were highest.