Tests for cooperative behaviour between stallions

Area of Science:

• Ethology
• Behavioral Ecology
• Mammalian Social Systems

Background:

• Feral horse populations exhibit both single-stallion and multistallion breeding groups.
• Theories of mutualism and reciprocal altruism have been proposed to explain multistallion band dynamics.
• Empirical evidence supporting these cooperative hypotheses is limited and contradictory.

Purpose of the Study:

• To empirically test the predictions of mutualism and reciprocal altruism in feral horse breeding groups.
• To compare stallion behavior and social structure in multistallion versus single-stallion bands.
• To identify alternative hypotheses that better explain the functioning of multistallion bands.

Main Methods:

• Comparative study of nine multistallion and 18 single-stallion bands in New Zealand.
• Observation and quantification of agonistic and affiliative behaviors between stallions.
• Analysis of factors influencing mare group size, stability, home range, and reproductive success.
• Assessment of dominant stallion aggression and subordinate stallion 'helping' behavior.

Main Results:

• Affiliative behaviors were less important than agonistic behaviors among stallions within bands.
• Stallion number did not positively influence mare group size, stability, or reproductive success.
• Dominant stallion aggression correlated positively with subordinate 'helping' but negatively with subordinate mating access.
• Multistallion bands exhibited significantly lower reproductive success.

Conclusions:

• Cooperative breeding hypotheses (mutualism, reciprocal altruism) are not supported for feral horse multistallion bands.
• Findings suggest mate parasitism or consort hypotheses may be more applicable.
• Dominant stallions showed intolerance towards subordinates who provided more defense but restricted their mating opportunities.