Invertebrate availability and vegetation characteristics explain use of nonnesting cover types by mature-forest songbirds during the postfledging period

Some species of mature‐forest‐nesting songbirds use regenerating clearcuts and forested wetlands during the postfledging period (between nesting and migration). Relatively dense vegetation structure and abundant food resources in non‐mature‐forest cover types have been hypothesized to explain this phenomenon. We examined the relative importance of vegetation structure and invertebrate availability on use of nonnesting cover types by adult and hatch‐year Ovenbirds (Seiurus aurocapilla) and American Redstarts (Setophaga ruticilla) during the postfledging period of 2009 in northern Minnesota. We used mist nets to sample bird use of forested wetlands and regenerating clearcuts of three age groups: 1–6, 7–12, and 16–19 yr after harvest. We modeled captures of birds using vegetation characteristics and invertebrate availability sampled around nets as explanatory variables. For all birds studied, captures were best explained by food availability and secondarily by vegetation characteristics including litter depth and woody debris for Ovenbirds and canopy height for American Redstarts. Shrub‐level invertebrate availability received a cumulative weight of 0.74–0.99 in Akaike's information criterion corrected ranked models for adult and hatch‐year birds of both species. Vegetation density and variation in vegetation density explained almost no variation in captures of either species. We conclude that both invertebrate availability and some vegetation characteristics influence use of nonnesting cover types by Ovenbirds and American Redstarts during the postfledging period, but that invertebrate availability is generally the stronger predictor of that use.