Comparative Nest-Site Habitat of Painted Redstarts and Red-Faced Warblers in the Madrean Sky Islands of Southeastern Arizona

Abstract

Conservation of avian species requires understanding their nesting habitat requirements. We compared 3 aspects of habitat at nest sites (topographic characteristics of nest sites, nest placement within nest sites, and canopy stratification within nest sites) of 2 related species of ground-nesting warblers (Red-faced Warblers, Cardellina rubrifrons, n = 17 nests; Painted Redstarts, Myioborus pictus, n = 22 nests) in the Sky Island mountain ranges of southeastern Arizona. These species nested in several forest and woodland cover types that occurred along an elevational gradient. Red-faced Warblers nested primarily toward the upper end of that gradient, in pine (Pinus spp.)—oak (Quercus spp.) and mixed-conifer forests. Painted Redstarts nested primarily at lower elevations, in riparian forest, oak-pine woodlands, and pine-oak forest. The 2 species both nested in cover types that occurred at mid-elevations. Within these shared cover types, Red-faced Warblers nested at higher elevations and at nest sites with greater canopy cover >10 m aboveground than Painted Redstarts. Nest placement within nest sites was similar between species; both placed their nests in concealed locations. Our results suggest that managers should consider the entire elevational gradient surveyed here to best conserve habitat for both species, and should maintain at least some areas with relatively dense understory cover across that gradient to provide cover for nest sites. Managers should emphasize lower overstories in lower-elevation oak-pine woodlands, taller overstories in higher-elevation pine-oak and especially mixed-conifer forests, and a mixture of overstory heights in mid-elevation pine-oak forests. We recommend additional detailed studies of nesting habitat and the effects of disturbance processes on nesting habitat. Such studies will add to our understanding of the ecology of these 2 bird species and habitat conservation in this ecologically important area.