Effect of social organisation on interspecific differences in overmarking behaviour of foals in African equids.

Overmarking remains an unstudied topic in juvenile mammals. We have previously documented a very high rate of overmarking by foals in four captive African equid species: mountain zebra (Equus zebra), plains zebra (Equus quagga), Grévy's zebra (Equus grevyi), and African wild ass (Equus africanus). African equids vary interspecifically in their social organisation. Since differences in social organisation affect many mammalian behaviours, in this study we investigated interspecific differences in overmarking behaviour of foals, analysing only cases where elimination of any other individual was explored by a foal. We hypothesised that the pattern of overmarking by foals should reflect either differences in social organisation of the species or phylogenetic relations among them. We found that in all species very young foals explored mostly maternal eliminations, and this preference declined with increasing age of the foal and reflected the social organisation of the species; the highest overmarking rate was in species with high intragroup aggression (mountain zebra) and lowest in species with low intragroup aggression and which form crèches (African wild ass). Similarly, the rate of overmarking of the mother, as opposed to other herdmates, was associated with social organisation of the respective species. Thus, we found interspecific differences in overmarking by foals, which were associated with variability in social organisation. Since we also revealed differences between African wild ass and zebra behaviour in early stages of ontogeny, we cannot refute the effect of phylogeny on overmarking behaviour. Additionally, our results supported the identity sharing hypothesis as an explanation of overmarking.