Multiscale Associations between Cavity-Nesting Birds and Features of Wyoming Streamside Woodlands

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Abstract
From 1982 through 1984, we studied riparian habitat use by cavity-nesting birds on three spatial scales: (1) nest trees, (2) nest sites (vegetation surrounding nest trees), and (3) disjunct fragments (0.1 to 32.3 ha) of floodplain forest. Nest cavities and nest trees differed substantially among bird species in terms of tree diameter at breast and nest height, nest height, nest-entrance diameter, whether the nest was in a limb or bole, and whether the nest entrance pointed above horizontal, horizontally, or below horizontal. Nest trees also differed significantly form randomly selected trees with respect to tree species and whether they were snags or nonsnag trees. Nest-entrance bearing did not differ significanlty among species or from random. Distances between nest trees and the nearest section of stream differed significantly among some species. Habitats at species'' nest sites and at randomly selected sites were indistinguishable in terms of shrub cover, tree density, snag desnity, vertical space between upper and lower canopies, distance to edge, and distance to opening. The size, shape, degree of isolation, and vegetative structure of habitat fragments significantly influenced species richness and abundance. Features of Wyoming streamside woodlands on all three spatial scales influence habitat use and are important in structuring communities of cavity-nesting birds. Some patterns of habitat use on the scales of nest trees and habitat fragments were not predictable from habitat associations observed elsewhere for the same species. Bird-habitat relations on one scale were (or were not) predictable from relations on other scales, depending on the species.