Feral horses at the city gate: ecological insights and rewilding opportunity

The decline of semi-natural open ecosystems after land abandonment is a conservation issue in many industrialized countries. Large herbivores, such as horses (Equus ferus), are excellent candidates for rewilding activities, as they can contribute to reducing loss of open landscapes. However, their presence could affect the spatio-temporal distribution of sympatric species, especially if the reintroduction is unplanned and uncontrolled. La Calvana, central Italy, is a protected area with a mammalian community that has never been systematically monitored, and its grasslands, which are a high conservation priority, are disappearing. The area hosts a population of feral horses that originated about 40 years ago from a few released domestic individuals, and their unplanned presence could represent a unique rewilding opportunity for the restoration of the abandoned landscape. Yet nothing is known about their distribution or relationships with sympatric mammals. By deploying 40 camera traps in May-July 2022, we systematically monitored the area to investigate spatio-temporal patterns of feral horses and their relationships with environmental, biotic, and anthropogenic factors. We detected 12 wild mammal species and estimated that horses were present in 40% of the study area. None of the environmental variables tested affected the occupancy of horses, although modeling of site-use intensity revealed that this species used upper-ridge grasslands more frequently. This suggests the area is suitable to support the population and that their presence at higher elevations can be an asset to preserving grasslands by limiting forest and shrub encroachment. Horses occupancy was not related to the relative abundance of wild ungulates, suggesting minimal competition for resources at present. However, the lower temporal overlap at sites with greater vegetation cover during the hottest hours indicated dominance of horses. Feral horses seem unaffected by human proximity, although they are occasionally subject to poaching. Lastly, the 7-year-long population census revealed a 12% annual growth rate that may lead to exceeding the carrying capacity of the ecosystem in the future. We recommend continued monitoring of this population and implementation of conservation and management programs.