Refuge-seeking and pest avoidance by feral horses in desert and island environments

Abstract

The hypothesis that insect harassment of feral horses results in the use of “refuge” sites to minimize pest pressures was examined. Patterns of resource exploitation were identified in two populations of feral horses ( Equus caballus), one in an insular mountain range in the deserts of Nevada and the other on a barrier island off the Atlantic Coast of Virginia and Maryland. Although physical features, amount and distribution of free water, and insect densities differed between the 2 study sites, horses displayed similar seasonal and daily patterns of habitat use. In the island horses, the rate of tail swishing/min was used as a crude measure of insect harassment. This behavior occurred least at beach and bay sites. These sites, in addition to the ocean, were used most during the summer, particularly between 10.00 to 16.00 h. In the desert population, the horses grazed in meadows early in the day when it was cooler and pest densities were lower. Movements shifted during the day, and horses rested on higher slopes and ridges primarily during the afternoon. Two new refuges for energy conservation were observed, viz. inshore water and snow patches. Resting occurred often in each of these areas.