Long‐term social structure data on small delphinids is lacking for most species except the bottlenose dolphin. This study describes the long‐term social structure of one community of Atlantic spotted dolphins, Stenella frontalis, divided into three social clusters. Data from 12 yr were analyzed using SOCPROG 2.3. Coefficients of association (CoA) were calculated using the half‐weight index. The overall mean community CoA ranged from 0.09 to 0.12. Temporal analyses and mantel tests revealed significant differences between sex class associations due to high male‐male CoA (0.12–0.23) compared to female‐female and mixed sex CoA (0.08–0.10). Female associations were strongly influenced by reproductive status, calf care, and social familiarity, but not by age class. Male associations were strongly influenced by age, access to females, and alliance formation. Males showed two levels of alliance formation, long‐term first order pairs/trios (CoA 0.70–1.00) and shorter‐term second order alliances between two or more first order alliances (CoA 0.45–0.69), and a possible third level during interspecies interactions. Mating strategies, sex, and cluster formation shaped the social structure in this spotted dolphin community. Similar to many bottlenose dolphin studies, long‐term affiliations for spotted dolphins were correlated with age, sex, and reproductive status.

Environmental variations can influence the structure of ecological communities that in turn alter the grouping and association patterns of social communities. This study compares the social structure of bottlenose dolphins in the Bahamas before and after two major hurricanes. Approximately 30% of regularly seen individuals disappeared after the hurricanes, with an equal number of immigrants arriving afterwards. The primary goal of this study was to quantitatively describe social structure changes occurring after this large-scale emigration (or death) and subsequent immigration of individuals using the social analysis program, SOCPROG 2.3. The pre-hurricane results revealed one community with association patterns that were consistent with previous work on this population as well as other welldocumented populations. Post-hurricane associations revealed that the community split into two distinct units, whose members associated highly within, but rarely between units. Association patterns varied between units. Immigrants assimilated well into the population, especially males. Over half of the post-hurricane associations involved immigrants, the majority between residents and immigrants, and primarily involving immigrant males. The costs/benefits of choosing to associate with an immigrant individual differ between males and females and may have been the driving force for the changes in social structure that occurred.

Extreme environmental events and demographic changes can have variable effects on the social structure of animal populations. This study compared the social structure of a community of Atlantic spotted dolphins in the Bahamas before and after two hurricanes. Approximately 36% of the individuals were lost, with no subsequent increase in immigration. The majority of the social structure characteristics were consistent with results from a long‐term study covering the previous 12 yr, including community structure with definitive social clusters, sex preferences and overall association patterns. However some changes occurred, though still constrained within sex preferences. Posthurricane there was a decrease in social differentiation and increased cohesion within clusters and across age class. Males retained or made new first order alliances, however, only one second order alliance was evident, revealing a simplified alliance structure. Juvenile individuals made alliance level associations, unprecedented from long‐term analysis. Although other studies have shown stark restructuring, this study showed that less drastic changes within overall social structure stability can occur. Persistence and evolutionary changes in populations through environmental and/or demographic perturbations may depend on the social structure of a population or community. Understanding the processes involved in social development is paramount for conservation of diverse populations.

Fission‐fusion dynamics typical of many delphinid populations allow for a variety of social grouping patterns. Identifying these groupings is crucial before conducting a detailed social structure analysis. This study analyzed the structure of a population of Bahamian spotted dolphins, Stenella frontalis. Through long‐term observations and preliminary analysis, three clusters were defined: Northern, Central, and Southern. To quantitatively investigate these delineations, we conducted analysis on 12 yr of sighting data using SOCPROG 2.3. Coefficients of association (CoA) were calculated using the half‐weight index, with individuals sighted six or more times per pooled period (3 yr each). Nonmetric multidimensional scaling (MD), hierarchical agglomerative cluster analysis and Mantel tests were conducted to determine if any divisions were present. Mantel tests and MD plots analysis supported the delineations into the three clusters. Cluster analysis showed cluster groupings, but with less clear distinctions between the clusters. The amount and strength of associations were significantly higher within clusters than between clusters. Based on behavioral and geographic overlap, these clusters did not meet the definition of separate communities and thus were termed social clusters. These fine scale, within community divisions, are biologically and socially important aspects of their community and are crucial in understanding the dolphins’ social structure.

With the exception of primates, detailed interspecies behavioral studies are rare in mammalian species and for cetaceans, most are anecdotal descriptions. This study is the first long‐term study on interspecies associations of regularly interacting groups. In the Bahamas Atlantic bottlenose (Tursiops truncatus) and spotted dolphins (Stenella frontalis) regularly form mixed species encounters (MSE). Both species show strong site fidelity with high resighting rates. During MSE, the majority (>65%) of spotted dolphins (especially males) were continually resighted; however bottlenose dolphins had comparatively low resighting rates (<17%). During MSE group size was significantly larger for spotted dolphins (13.0 ± 11.0) than bottlenose dolphins (4.8 ± 3.5) (F = 93.803, df = 1, P < 0.001). This difference was largest during aggressive encounters, due to the increased spotted dolphin group size (t‐test, t = 4.75, df = 184, P < 0.0001), but no difference in bottlenose dolphin group size. Strong associations (greater than twice the community average) were primarily between male spotted dolphins. Male alliances were prevalent for spotted dolphins but rare for bottlenose dolphins. These species differences were also observed in lagged association rates. These results highlight the differences involved in alliance formation and function for regularly interacting sympatric species and reveal insights into possible ecological and social reasons for these group formations.