Removal experiments indicate that subordinate stallions are not helpers.

This research study explores the role of subordinate stallions within groups of wild horses known as harems. The study found that the presence of these subordinate stallions significantly increased aggressive interactions among other stallions and towards mares, and that the dominant stallion was able to successfully protect the harem without assistance from the subordinate stallion.

Research Methods and Objectives

• The research aimed to investigate interactions between male horses in a harem, specifically focusing on the interaction between subordinate and dominant stallions. This was done to understand if the presence of subordinate stallions is necessary for the survival of the harem, or if they contribute to an increase in aggression.
• The researchers conducted an experimental study on six multi-stallion bands. They removed the subordinate stallion from two of these groups for three weeks during the breeding season and monitored the behavior of the remaining stallions and mares.
• Specific behaviors were monitored and their frequency was compared before the removal, during the subordinate’s absence, and upon his return. This included rates of intra- and inter-band stallion aggression, aggression towards mares, and the proximity between stallions and mares.

Key Findings

• The study found that the dominant stallion was able to successfully defend the harem in the absence of the subordinate stallion, indicating that the subordinates are not necessarily needed for harem defense.
• Furthermore, rates of aggression towards mares were substantially decreased during the absence of the subordinate stallion. This suggests that much of the heightened harassment of mares can be directly attributed to the presence of the subordinate, and not the dominant stallion or the mares themselves.
• Thus, the researchers concluded that the presumed cooperation between multiple stallions in a harem, as suggested by some theories, may not hold true. Subordinate stallions may play a more antagonistic role within a harem.

Implications and Further Research

• Based on these findings, the researchers suggested a different hypothesis that aligns better with their findings: mate-parasitism. In this scenario, subordinate stallions may not be involved in harem defense but may interfere and cause disruptions to increase their chances of mating.
• The study emphasized the need for further, more extensive research, to further test and validate its findings.