Tests for cooperative behaviour between stallions.

This study explored the behaviour of male horses, or stallions, in different group structures and found no evidence of cooperative behaviours, refuting theories of mutualism and reciprocal altruism. Rather, multi-stallion groups were observed to have lower reproductive success and dominant stallions tended to limit subordinates’ access to females.

About the Research

This research examined the interactions and behaviour of stallions within single-stallion and multi-stallion breeding groups in a wild horse population in New Zealand. The team investigated two primary theories of group behaviour: mutualism (the theory that members of the group cooperatively benefit one another) and reciprocal altruism (the theory of exchanging beneficial behaviours). Previous empirical data supporting these theories were deemed contradictory and insufficient.

• The researchers compared nine multi-stallion and 18 single-stallion bands in the wild horse population.
• They examined different elements of stallion behaviour and group structure, including agonistic (conflict-oriented) and affiliative (friendly or cooperative) behaviours, group size and stability, reproductive success, and more.

Key Findings

Across the observed behaviours and group dynamics, the study found no evidence of mutualism or reciprocal altruism in stallion behaviours. Stallions in multi-stallion breeding groups didn’t have better outcomes in group size, stability, reproductive success or quality of habitat.

• Agonistic behaviours were observed to be more common than affiliative behaviours within these groups.
• Interestingly, the study found that dominant stallions were less tolerant of and less likely to allow subordinate stallions proximity to mares, especially if those subordinates exerted effort in defending the group of mares.
• This suggests a negative relationship between the ‘helping’ effort by subordinate stallions and their ability to mate with mares in their band.
• Multi-stallion groups were found to have potentially negative impacts on reproductive success.

Conclusions and Implications

Given these findings, the researchers rejected the cooperative hypotheses for multi-male breeding groups in horses. They suggested that mate parasitism (where one male usurps another’s mate) and the consort hypothesis (where males follow and guard females during their fertile period) would be better alternatives to explain group behaviour.

Ultimately, the study underlined the importance of understanding animal behaviour and social structure in wild populations. Recognizing how different group structures and interactions can impact reproductive success can offer valuable insights into population dynamics and species conservation.