Vegetation characteristics are commonly invoked to explain differential nesting success, but few studies have identified how habitat attributes may be associated with specific predator groups responsible for nest losses. We measured vegetation characteristics at artificial songbird
nests deployed on and above the ground in mixedwood forest in west-central Alberta, to discriminate characteristics of successful nests from those of nests destroyed by mice and voles, squirrels, and birds. Successful nests, and those depredated by mice and voles, tended to be on the ground
and were well concealed by dense shrubs. Squirrels and birds usually raided aboveground nests at sites with few shrubs and high tree densities. These results suggest that nest visibility is a major factor influencing risk of predation, but the relative importance of concealment varies according
to the types of predators and their behavior. The characteristics of nests from which eggs were removed, leaving no egg remains to identify predators, closely resembled those of nests visited by squirrels and birds. Our findings have implications for how individual songbird species cope with
selection pressures imposed by nest predators associated with vegetation characteristics of birds' nest patches and, ultimately, how predators may shape the structure of avian communities.
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