DOES MOBILITY OR SEX OF VOLES AFFECT RISK OF PREDATION BY MAMMALIAN PREDATORS?

Abstract

Animals gain fitness benefits if they can increase their survival prospects by reducing mobility under temporarily high predation risk. We used miniature radio collars to determine whether mobility affects the risk of predation on breeding field voles (Microtus agrestis) and sibling voles (M. rossiaemeridionalis) by their main predators, small carnivores, in a population with cyclically fluctuating numbers and predation risk. There was a significant association of mobility with predation risk: voles killed by small carnivores moved more than did voles that survived. An experimental reduction of predation risk significantly affected vole mobility: voles moved more under reduced predation risk. Sex, season, and phase of the vole cycle explained a similar or larger proportion of the observed variation in the number of killed voles than did mobility. Carnivores killed more female than male voles, predation risk was higher in the decline phase than in the increase phase of the cycle, and predation risk was also higher in spring than in early summer. However, voles cannot change sex, season, or the phase of their cycle, whereas they can alter their mobility. These results offer novel observational and experimental support for the hypothesis that animals may increase their survival prospects by reducing mobility. The female-biased prey choice of small carnivores implies that they have a stronger impact on prey population dynamics than avian predators, which have previously been shown to kill more males than females.