Visibility and vigilance:: Behavior and population ecology of uinta ground squirrels (Spermophilus armatus) in different habitats

Ground squirrels are often described as preferring open grassland habitats to increase their chances of locating predatory threats while visually surveying their surroundings. This description is often based on the assumption that ground squirrels require clear views to promote detection of predators. We studied a population of Uinta ground squirrels (Spermophilus armatus) inhabiting patches of grassland and sagebrush in the northern range of Yellowstone National Park to determine if the presence of view-obstructing vegetation would be associated with differences in vigilance behavior of individuals. We also compared rates of weight gain and population estimates in grassland and sagebrush patches to determine if these factors would vary in association with differences in time budgets and perceived risk of predation in these patch types. Although there were differences among sites in time spent foraging and maintaining vigilance, these differences were not consistent between sites of similar habitat and degree of visual obstruction. These results suggest that the relationship between visibility and vigilance for this species may be complicated by the dual nature of shrubs as visual obstructions and as protection from attacking predators. The relationship between these 2 factors will likely influence how prey species respond to alterations to the vegetative structure of their environments. Ground squirrels, specifically, appear to be capable of adapting to variation in the structure of the vegetation and will likely thrive as long as an abundance of grasses are available to provide fattening seeds for forage.