Microhabitat use and behavior of voles under weasel and raptor predation risk: predator facilitation?

Abstract

An example of predator facilitation is that a microhabitat shift in a prey species induced by one predator increases the probability of the prey falling victim to other predators. Least weasels (Mustela nivalis) hunt in dense plant cover, whereas kestrels (Falco tinnunculus) hunt in habitats with sparse plant cover. Field voles (Microtus agrestis), the main food of weasels and kestrels, prefer open country with a high grass layer. We simulated a multipredator environment in an aviary (3.0 X 4.8 X 2.2 m) to find out whether predator facilitation plays a role in the interactions between voles, small mustelids, and raptors. In each replicate, we placed a field vole in a pen including sides of high and low grass layers (cover and open). In a predator-free situation, voles preferred cover but shifted to open when a weasel was introduced to cover. In the presence of a kestrel, voles occupied cover and decreased their mobility. In the presence of a weasel plus a kestrel, voles behaved as under the kestrel risk alone. Therefore, in these aviary circumstances, voles perceived the kestrel risk as greater than the weasel risk. Predator facilitation in the assemblage of predators subsisting on rodent prey may contribute to the crash of the four-year vole cycle: microhabitat shift due to an avoidance of weasel jaws may drive voles to raptor talons. Key mords: antipredatory behavior, field vole, four-year vole cycle, kestrel, least weasel, microhabitat shift, predator facilitation. [Behav Ecol 7:30-34 (1996)]