In the Arctic tundra, snow is believed to protect lemmings from mammalian predators during winter. We hypothesized that snow quality (depth and hardness) should affect mammalian predation rates on lemmings, but that this effect would depend on the predator hunting strategy; and that predation by ermines (Mustela erminea), which can hunt lemmings under the snow, should be higher in preferred lemming habitats. We measured snow depth and hardness at tunnels made by arctic fox (Vulpes lagopus) predation attempts, at winter nests nonpredated and predated by ermines, and at random locations. We also determined winter nest density in 3 habitats (wet, mesic, and gully). Deep and hard snow restricted fox predation attempts made by jumping through the snow, but not those made by digging. Ermine predation was unaffected by snow depth and weakly by nest density but was higher in gully and intermediate in mesic habitats, which are conducive to high snow accumulation, compared to the wet habitat. These results indicate that habitat-related topographical features are more important than snow depth or nest density per se in affecting the winter foraging strategy of ermines. Overall, even though we found a relatively weak effect of the snow cover on predation by foxes and ermines, it is difficult to predict how upcoming changes to the snow cover will affect lemming vulnerability to mammalian predators because a wide range of snow conditions may result from climate warming.
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Vol. 94 • No. 4