WEASELS, VOLES, AND TREES: INFLUENCE OF MUSTELID SEMIOCHEMICALS ON VOLE POPULATIONS AND FEEDING DAMAGE

Abstract

The role of predators, particularly small mustelids, in regulating vole (Microtus spp.) populations has been the subject of much scientific inquiry over the past several decades. From a management perspective, voles cause economic damage by feeding on seedlings planted on cutover forest land in temperate and boreal zones. Because of the close relationship between small weasels (Mustela erminea and M. nivalis) and voles, could the indirect effect of weasel scent disrupt vole populations and reduce their damage to forest plantations? This study was designed to test the hypotheses that synthetic weasel odor would: (1) reduce abundance, reproduction, survival, and movement of montane (Microtus montanus) and meadow (M. pennsylvanicus) vole populations; (2) enhance the activity of small weasels; and (3) reduce feeding damage by voles to tree seedlings. Study areas were located near Summerland and Gavin Lake in south‐central British Columbia, Canada. Vole populations were intensively live‐trapped on replicate sites from April 1994 to May 1995 during a peak year in abundance. Synthetic weasel odor was continually present on treatment sites from early summer 1994 to spring 1995. Weasel activity was measured by the number of individuals captured in live‐traps and by the number of snow tracks on control and treatment sites. Overwinter mortality to planted lodgepole pine (Pinus contorta) seedlings from vole feeding was measured on all sites in May 1995.Mean vole abundance (n = 4) was similar between control (32–121 voles/ha) and treatment (37–118 voles/ha) sites. Montane voles declined by 17–36% on treatment sites during early summer when trappability of this species declined dramatically at Summerland. This pattern was not observed for meadow voles at Gavin Lake. Recruitment of new voles was generally similar between control and treatment sites. Weasel odor had no effect on reproduction, in terms of number of successful pregnancies and index of early juvenile survival, or on total survival, movements, or body mass of voles. Activity of small weasels appeared to be higher on treatment than control sites at Gavin Lake. Weasel odor did not reduce mortality of tree seedlings caused by vole feeding.This study is the first investigation of the population responses of free‐living voles to synthetic odor of the short‐tailed weasel, a principal predator of Microtus spp. Our results demonstrate that by the time voles have reached high densities, it is too late to reduce numbers or curtail feeding damage, regardless of weasel odor‐induced antipredatory behavior or enhanced activity of predators. Application of weasel odor during the low phase of the vole population cycle would be a critical test of the hypothesis that small mustelids could lengthen the period of low vole numbers and potentially protect forest plantations from vole damage.