INFLUENCE OF HABITAT ON BEHAVIOR OF TOWNSENDS GROUND-SQUIRRELS (SPERMOPHILUS-TOWNSENDII)

Trade-offs between foraging and predator avoidance may affect an anima l's survival and reproduction. These trade-offs may be influenced by d ifferences in vegetative cover, especially if foraging profitability a nd predation risk differ among habitats. We examined above-ground acti vity of Townsend's ground squirrels (Spermophilus townsendii) in four habitats in the Snake River Birds of Prey National Conservation Area i n southwestern Idaho to determine if behavior of ground squirrels vari ed among habitats, and we assessed factors that might affect perceived predation risk (i.e. predator detectability, predation pres sure, pop ulation density). The proportion of time spent in vigilance by ground squirrels in winterfat (Krascheninnikovia lanata) and mosaic habitats of winterfat-sagebrush (Artemisia tridentata) was more than twice that of ground squirrels in burned and unburned sagebrush habitats. We fou nd no evidence for the ''many-eyes'' hypothesis as an explanation for differences in vigilance among habitats. Instead, environmental hetero geneity, especially vegetation structure, likely influenced activity b udgets of ground squirrels. Differences in vigilance may have been cau sed by differences in predator detectability and refuge availability, because ground squirrels in the winterfat and mosaic habitats also spe nt more time in upright vigilant postures than ground squirrels in bur ned-sagebrush or sagebrush habitats. Such postures may enhance predato r detection in low-growing winterfat.