Predation on meadow voles : predator response to vole abundance and vole response to predator exclusion in Red Rock Lakes National Wildlife Refuge, Montana
Burgener, Joel Ryan.
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Small mammals such as meadow voles exhibit complex and puzzling multi-annual population cycles. Predators can have an effect on these cycles though the precise relationship is not completely understood. I undertook this study to 1) quantify the response of predators to small mammal abundance and 2) determine the relative roles of mammalian meso-predators and raptors on abundance and survivorship of small mammals in wet meadow habitat at Red Rock Lakes National Wildlife Refuge, southwest Montana. as well as the response by predators to different levels of small mammal abundance. Two randomly placed trapping grids were placed inside three adjacent grazing units. Two additional treatment trapping grids were placed inside one of the grazing units with an electrified polywire fence to exclude mesopredators. The trapping occurred in July and August of 2010 on the Refuge. The trapping occurred in three primary sessions with four individual trapping days (secondary sessions) per primary session in each grazing unit. Predators were monitored by conducting visual raptor surveys and camera trapping. My results indicated that partial predator exclusion did not improve vole survivorship in fact some raptors used the fence posts as supplemental perches, as some bore signs of use. My results also did not support the hypothesis that raptor abundance tracked vole abundance. However, vole abundance was significantly higher during 2010 than in previous years. The increase in vole abundance resulted in other factors driving habitat selection by raptors. The camera traps did not provide any information about the use of the wet meadow by mammalian predators, however other signs of mammalian predators were observed in the trapping area during the study. Further study may shed more light on the use of supplemental perches by raptors and how mammalian predators are using the wet meadow habitat on the Refuge.