Based on 13 structural variables, the habitat structure of 16 species of wood warblers breeding in north-central Minnesota can be divided into three general habitat types: open country, shrub-forest edge, and mature forest. Reciprocal averaging ordination produced a gradient of habitat relationships from forest to open country species, the latter being somewhat distinct. Based on principal components analysis, most species had habitats with variable vegetation structure. These habitat characteristics are discussed in relation to competition theory.The habitat of the Black-throated Green Warbler (Dendroica virens) was examined at five sites in the north-central and northeastern United States. Principal components analysis of 13 habitat variables showed between site differences in canopy height, tree size, canopy cover, and percent of coniferous vegetation. Although some sites supported unique plant community-types, tree species composition was not related to differences in habitat structure. Instead, habitat differences were mostly attributable to differences in the structure of the vegetation.Habitat relationships of wood warblers (Parulidae) were examined for within-territory, within-region, and between region patterns. By examining nest-site versus song perch site vegetation structure, within-territory variation was identified. Circular samples of vegetation structure should be centered not only on song perch sites, but also on nest-sites or female foraging areas because song perch sites alone may over-estimate the tree component in the habitat of some species
