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

Patterns of resource exploitation were examined among 2 populations of feral horses in the USA, to investigate whether harassment by insects results in the use of ’refuge’ sites to minimise pest pressures. In the first study site, Assateague, a barrier island off the Atlantic coast of Maryland and Virginia, the common tabanids were Tabanus nigrovittatus Macq., T. lineola F., Chrysops fuliginosus Wied., C. atlanticus Pechuman and Stomoxys calcitrans (L.). The 2nd study site was the Granite Range, in the Great Basin Desert, Nevada, where the altitude ranges from 1291 to 2786 m. the tabanids present there were T. aegrotus O.-S., T. atratus F., C. furcatus Wlk. and C. fulvaster O.-S.. Though physical features (such as water availability and insect densities) differed between the 2 study sites, the horses displayed similar seasonal and daily patterns of habitat use. The island horses displayed less tail swishing while near the beach area and frequented this area most during the summer, especially between 10.00 and 16.00 h. In the desert, the horses grazed in meadows early in the day when the pest densities were lowest. During the afternoon, the horses rested on higher slopes and ridges. It is concluded that inshore water and snow patches are refuges for energy conservation.