The partial merger of two dolphin societies

Area of Science:

• Marine Biology
• Animal Behavior
• Dolphin Social Dynamics

Background:

• Mammalian social groups typically exhibit antagonism, cooperating to defend resources from non-members.
• Resource defense is challenging in the three-dimensional marine environment, influencing social structures in Delphinidae (dolphins).
• Atlantic spotted dolphins (Stenella frontalis) display fission-fusion grouping patterns and strong male-male associations.

Purpose of the Study:

• To document and analyze the long-term partial fusion of two distinct Atlantic spotted dolphin communities.
• To investigate the social interactions and bond formation between individuals from immigrant and resident dolphin groups.
• To assess potential changes in social behavior and intergroup interactions following the immigration event.

Main Methods:

• Long-term observational study of two Atlantic spotted dolphin communities over 20 and 30 years, respectively.
• Monitoring a 160 km immigration event of a northern community into the southern community's range.
• Analysis of social grouping patterns, association levels, and affiliative contacts between individuals from both communities over a 5-year period post-immigration.

Main Results:

• Following immigration, members of all age classes and both sexes were observed in mixed groups, with a bias towards immigrant males.
• High levels of association were observed between males and females from different communities, comparable to within-community associations.
• Frequent affiliative contacts between individuals from the two communities indicated the formation of new social relationships.

Conclusions:

• The partial fusion of two Atlantic spotted dolphin communities resulted in the formation of new social bonds and relationships.
• This inter-community mixing, characterized by affiliative interactions, is rare among mammals and suggests diminished 'outsider' aggression in Stenella frontalis.
• The findings imply that ecologically similar dolphin species may also exhibit reduced intergroup antagonism compared to terrestrial mammals.