Habitat Relationships of Wood Warblers (Parulidae) in Northern Central Minnesota

Abstract

To analyze the habitat relationships of 16 species of wood warblers (Parulidae) breeding in northern central Minnesota, thirteen variables of the structure of the habitat were measured in 207 0.04-ha circular plots located in the territories of breeding males. Cluster analysis of the average habitats of the species identified three groups of species occupying (1) shrub-forest edge (D. magnola, Mniotilta varia, Setophaga ruticilla, V. ruficapilla, Wilsonia canadensis), (2) mature forest (D. coronata, D. fusca, D. pinus, D. virens, Seiurus aurocapillus, Parula americana), and (3) open fields with shrubs (Dendroica pensylvanica, D. petechia, Geothlypis trichas, Oporornis Philadelphia, Vermivora chrysoptera). A reciprocal averaging ordination of the average habitat of each species produced a two-dimensional ordination. The first axis extends from forest vegetation to habitats with few trees and dense ground cover. A second axis separates areas of coniferous forest from those of younger deciduous and mixed forest. A principal components analysis of 199 samples permitted the construction of ellipses that reflect the variability and overlap in the habitat of each species. The axes in these ordinations are multivariate resource axes, but we refrain from interpreting the results in terms of niche width and overlap. Instead we think the distribution of the species and the variation within the habitat of each are mainly attributable to affinities to biotic resources such as food, nest sites, and certain elements of the structure of the vegetation. To infer that these relationships represent the results of interspecific interactions is not justified.