What factors influence horse distribution patterns on Sable Island?

Abstract

Sable Island is a long, narrow sandbar off the coast of Nova Scotia, Canada. Despite its small size the island has been home to a population of feral horses (Equus ferus caballus L.) since the early 1800s. These horses are a valuable study population as they are isolated by law from human interference, and manage to survive in a confined space with limited resources. This study investigates their movement patterns, specifically whether social status and seasonal changes may be influencing variation in movement and distribution among individuals. It was predicted that stallions - male horses that are the designated ‘leader’ of a band - should have smaller ranges than bachelor horses because their movement may be restricted by their close associations to mares. It was also predicted that range distances would be greater in winter than in summer due to the high winds and limited grazing options on the island during winter. These questions were examined using GPS (global positioning system) data representing the locations of a subset of the horses over a three year period (2008-2010). The results suggest that seasonal changes substantially affect the average position of stallions on Sable Island, likely due to differential resource and shelter availability across the island in different seasons. The data also showed that range was most heavily influenced by individual identity, which indicates that different horses have different range tendencies regardless of their social status or the time of year. However, not all of the variation in distribution and movement of the horses could be attributed to the variables investigated in this study. Further research into other factors and the resource distribution on the island will provide a clearer picture into the dynamics at play within this population.