Abstract
Ecological factors such as habitat and food availability affect the social structure of bottlenose dolphins (Tursiops spp.). Here, we describe the social structure of bottlenose dolphins (T. truncatus) in Golfo Dulce, Costa Rica, a semi-enclosed, fjord-like tropical embayment resembling a pelagic system. We also examine behaviour-linked social strategies by comparing social structure relative to behavioural state: feeding versus non-feeding. We analysed 333 sightings over 210 days from boat-based surveys. Despite the uniqueness of the area, the 47 analysed adults had a social structure similar to other populations: a well-differentiated fission–fusion society with sex-specific patterns of associations and aggression. These results indicate that differences in social structure relative to other populations were a matter of degree. Association strength of dyads was highly correlated across behavioural states, indicating constraints on social fluidity. Males displayed a marked difference in lagged association rate and females displayed a small difference in association homogeneity between states. We suggest this difference in population-wide social connections between behavioural states, particularly for males, was due to mating strategies, a pressure which is strongest during non-feeding behaviour and relaxed during feeding. This finding highlights the importance of considering behavioural state when examining individual bonds and the behavioural plasticity for which the bottlenose dolphin is well known.
Highlights
The social structure of Golfo Dulce bottlenose dolphins (Tursiops truncatus) and the influence of behavioural state
Males displayed a marked difference in lagged association rate and females displayed a small difference in association homogeneity between states. We suggest this difference in population-wide social connections between behavioural states, for males, was due to mating strategies, a pressure which is strongest during non-feeding behaviour and relaxed during feeding
Our study indicates that bottlenose dolphins from a unique environment close to the equator have a similar social structure as that of populations from other latitudes
Summary
The social structure of Golfo Dulce bottlenose dolphins (Tursiops truncatus) and the influence of behavioural state. We describe the social structure of bottlenose dolphins (T. truncatus) in Golfo Dulce, Costa Rica, a semi-enclosed, fjord-like tropical embayment resembling a pelagic system. Despite the uniqueness of the area, the 47 analysed adults had a social structure similar to other populations: a well-differentiated fission–fusion society with sex-specific patterns of associations and aggression. Bottlenose dolphin society is categorized as fission–fusion, characterized by fluid relationships where individuals associate with a number of other individuals over time [9] Within this fission–fusion framework, sex-specific patterns are common, and may be due to differences in encounter rate and utilization time of the main reproductively limiting resource of each sex, food for females and mates for males [10]. We hypothesized that the unique combination of resource predictability and composition (relatively isolated topography, unpredictable water inflow and pelagic food resources) would be correlated with a unique social structure
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