Nest-site Selection and Nesting Success of Cavity-nesting Birds in High Elevation Forest Drainages

ABssAcr.-We identified habitat features that characterized successful and unsuccessful nest sites, nest sites vs. random sites, and differences among coexisting species of cavitynesting birds for 356 nests in central Arizona. Live and, more commonly, dead quaking aspens (Populus tremuloides) were used for 88% of all nest sites, but aspens constituted only 12% of all trees in random plots (n = 152). Nest patches (11.3-m-radius circle centered on the nest tree) of most bird species contained significantly more aspens and conifers, which provided foraging substrates for cavity-nesting species, than random plots, but the patches had fewer deciduous trees (except aspens). Thus, more potential nest sites and foraging substrates existed in chosen nest patches than in random plots. Failed nests generally were more concealed by foliage and were closer to conifers. Nest success was lower for species with lower nest height. Reduced nest success at lower and more concealed nests may occur because predators are more successful. Nonexcavator species had lower nesting success than excavator species possibly because they nested lower, had greater nest concealment, used older cavities, and tended to have smaller body mass. Received 21 May 1990, accepted 26 November 1990.