Cover and efficacy of predator-based repellents for Townsend's voleMicrotus townsendii.

Predator-based repellents have been used experimentally to control wildlife damage in both agriculture and forestry, but they have not always been effective. We examined the relative importance of cover and predator odors in forage patch selection by Townsend's vole,Microtus townsendii, and its behavior related to cover and predator cues. Experiments were conducted in which forage patch and area choices were related to available habitat alternatives. Outdoor enclosures were divided into halves: one side was treated and the other used as a control. Treatments consisting of "cover," "repellent," and "cover plus repellent" were compared to controls (no cover, no repellent). In the absence of cover, voles preferred to feed on the side without repellents. When cover was present, voles preferred to feed on the side with cover, regardless of whether or not repellents were present. Voles visited more feeding stations on the side without cover when repellents and cover were present than they visited during cover-only treatments. These additional feeding stations, visited outside of cover, were used only lightly as food sources. The amounts of oats eaten by voles decreased with increasing distance from cover. This inverse relationship had a steeper slope in coveronly treatments compared to cover plus repellent treatments. A selection model based on forage patch selection and a habitat preference hierarchy is proposed. We conclude that predator odors are effective as repellents, but their efficacy depends on habitat conditions. Managers intending to use predator-based repellents must ensure that alternative sites available to pests are better quality habitat than in areas to be protected.