Determinants of the Use of Habitat by Horses in a Mediterranean Wetland

Abstract

The distribution of horses living in semi-liberty in 335 ha of a Mediterranean deltaic environment has been studied over 6 yr as part of a broader program of research on the behavior and ecology of the horses. The herd as unmanaged and developed a wild type social structure. For most of the period all individuals used the whole area; there was no territorial defense and social behavior appeared to have no effect on the horses'' selection of habitat. The study area was stratified into 8 units using landscape classification. These units contained very different plant communities with different structures and annual cycles of growth, the extremes being deep marshes colonized by reeds which grew to a height of 60 cm in March-Oct.; and coarse grasslands at the top of the catena. These were dominated by perennial grasses .apprx. 10 cm high, which showed some growth all through the year. The distribution of the horses between these units was analyzed in terms of some environmental parameters. Though the weather and biting insects had some effects on the horses'' distribution particularly for non-feeding activities, the abundance of their food was the only good predictor of their habitat preferences for feeding activities. The horses preferred the areas with the greatest concentrations of high quality food (green plant matter) as long as areas with a reasonable concentration (> 90 g m-2) were available. The threshold at which an area was preferred increased as the availability of green matter increased. When green plant matter became sparse, at the end of winter, the horses'' tactic was to search out the areas with the greatest concentrations of perennial herbaceous plants, green or dead. The primary function of selection of feeding habitat by these horses was to maximize their intake of high quality food.