Population numbers of many bird species associated with early-successional or disturbance-dependent habitat types are declining. We used an information–theoretic approach to evaluate hypotheses concerning factors affecting breeding bird densities in different early-successional habitat types. We studied shrubland bird communities in 3- to 5-year-old regenerating forest (n = 3), glade (n = 3), and forest–pasture edge (n = 3) habitat types in the predominantly forested Missouri Ozarks in 1997–1999. We monitored 8 bird species using spot mapping and total mapping techniques, searched for and monitored nests, and measured vegetation structure within nested circular plots. In evaluating breeding densities in these habitat types, we compared support for a global model with year, habitat type, and a habitat type × year interaction to several reduced models and a null model with only an intercept, and we used model-averaged coefficients to evaluate effect size. We found support for the effects of habitat type on breeding densities of prairie warbler (Dendroica discolor) and yellow-breasted chat (Icteria virens); the effects of habitat type and year on densities of blue-winged warbler (Vermivora pinus), eastern towhee (Pipilo erythrophthalmus), and field sparrow (Spizella pusilla); the effect of year on densities of indigo bunting (Passerina cyanea) and northern cardinal (Cardinalis cardinalis); and no effects on densities of white-eyed vireo (Vireo griseus). The effect size of habitat type on breeding densities varied among species and indicated important species-specific differences in habitat use. Most shrubland bird species used both glades and regenerating forests more than forest–pasture edge sites, and breeding densities of some species were higher in regenerating forests than in glades. For some species, patterns in reproductive success (reported as interval nest success) mirrored observed patterns in breeding densities. However, substantial variation existed among species with respect to patterns in habitat use and nest success. Conservation planning for the persistence of birds requiring early-successional habitat types should consider the ephemeral nature of these areas and the potential contribution from young, regenerating forest.
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Vol. 70 • No. 1