The social organisation of feral donkeys ( Equus asinus) on a small Caribbean island (St. John, US Virgin Islands)

Abstract

The grouping patterns of feral donkeys ( Equus asinus) on St. John, a small tropical island in the Caribbean Sea, were recorded from June 1984 through September 1985. Eighteen different grouping patterns (social units) were observed for adult donkeys. A significant difference in social organisation between the sexes was found. The most common adult female social grouping was composed of one or more adult females and their offspring. Solitary males were the most commonly observed social unit for adult male donkeys. All social units except that of an adult female and her most recent offspring were unstable. Results from this study are compared to those from studies on two other feral donkey populations in the United States, both inhabiting very different habitats from each other and also from the St. John population. One was observed in the temperate desert region of Death Valley in the western United States and the other on Ossabaw Island, a small island of mild temperate climate off the coast of the eastern United States. Although percentages of donkeys in various social units are significantly different, the overall social organisation of the St. John donkeys is more similar to that of feral donkeys in Death Valley than to the stable harem bands seen for the donkeys on Ossabaw Island. The social systems of all three populations are variations of the system seen for their ancestral species, the true wild ass of northern Africa. An examination of habitat differences among the three feral donkey populations as well as a population of true wild asses studied in the extremely hot and arid Danakil Desert of Ethiopia, and the effects of these differences on the mating systems of these populations, has led to the formulation of a hypothesis for the variation seen in social organisation. The ability of E. asinus to adopt very different social organisation strategies in response to differences in environmental circumstances helps to explain why this species has been so successful at establishing thriving feral populations around the world.