Dolphins form largest alliance network outside humans

Press release issued: 29 August 2022

Male bottlenose dolphins form the largest known multi-level alliance network outside humans, an international team led by researchers at the University of Bristol have shown. These cooperative relationships between groups increase male access to a contested resource.

The scientists, with colleagues from the University of Zurich and University of Massachusetts, analysed association and consortship data to model the structure of alliances between 121 adult male Indo-Pacific bottlenose dolphins at Shark Bay in Western Australia.

Male dolphins in Shark Bay form first-order alliances of two-three males to cooperatively pursue consortships with individual females. Second-order alliances of four-14 unrelated males compete with other alliances over access to female dolphins and third-order alliances occur between cooperating second-order alliances.

“Not only have we shown that male bottlenose dolphins form the largest known multilevel alliance network outside humans, but that cooperative relationships between groups, rather than simply alliance size, allows males to spend more time with females, thereby increasing their reproductive success.”

Read the full University of Bristol news article

Paper: Connor RC et al. (2022). Strategic intergroup alliances increase access to a contested resource in male bottlenose dolphins. PNAS. https://www.pnas.org/doi/full/10.1073/pnas.2121723119