Test of four hypotheses to explain the function of overmarking in foals of four equid species.

This research seeks to explain the function of overmarking (one animal placing its scent mark over another’s) observed in juvenile equids. Four hypotheses about this behavior were tested among foals of four different African equid species, and the results favor the theories that overmarking helps to share identity between foal and mother and it starts as early expression of male sexual behavior.

Research Scope and Methodology

• The study aimed to investigate the puzzling behavior of overmarking, which is the action of one individual placing its scent mark directly on top of another’s, focusing on juvenile equid species. The research specifically tested four hypotheses to explain this behavior.
• The observations were conducted on 43 foals, from a sample of 108 individuals. The individuals belonged to four different African equid species (Equus africanus, E. grevyi, E. quagga, E. zebra) and were housed in five different zoos.
• The researchers recorded a total of 3340 eliminations, out of which 260 were instances of overmarking by 38 individual foals across all the species.

Hypotheses Tested

• The first hypothesis was that overmarking served to conceal the individual’s scent identity.
• The second hypothesis suggested that overmarking was an announcement of association with other group members, particularly the mother. This implied that overmarking functioned to share identity with the mother.
• The third hypothesis proposed that overmarking was a strategy used by the foals to prevent the next conception of the mother, thus representing a parent-offspring conflict.
• The fourth hypothesis assumed that overmarking was an early expression of male sexual behavior.

Key Findings

• The behavior of overmarking was observed in a significant proportion of the foals studied, with one of the highest recorded rates of overmarking by mammalian juveniles.
• Overmarking was noticeably more frequent in male foals than in female foals.
• Foals of all species studied, except the African wild ass, engaged more in overmarking the mother than another herdmate. This was interpreted as probable evidence of shared identity between the mother and the foal.
• Furthermore, mother equids also tended to overmark their foals, though not exclusively their own offspring.
• The overall results support the hypotheses that overmarking serves to share identity between foal and mother and that it might be an early expression of male sexual behavior.