The Effect of Nest Predation on Habitat Selection by Dusky Flycatchers in Limber Pine-Juniper Woodland

Abstract

Habitat selection by Dusky Flycatchers (Empidonax oberholseri) was examined in limber pine-mountain juniper (Pinus flexilis-Juniperus scopulorum) woodland in western Wyoming during the breeding seasons of 1986, 1987, and 1988. Vegetation characteristics associated with occupied habitat were measured (1) at the nest site, (2) within the 0.04-ha nest patch, and (3) in the breeding territory outside the nest patch; results were evaluated in relation to availability within the habitat type and nesting success. Breeding pairs of Dusky Flycatchers occupied nest patches with greater foliage cover and greater density of trees than was generally available; territories were associated with greater densities of snags and a smaller proportion of trees with dead branches extending outside the canopy than was generally available, although selectivity at the territory scale was relatively weak. Successful pairs of Dusky Flycatchers had nests with greater concealment from below, shorter distances from the nest tree to the nearest tree, and greater densities of small trees in the nest patch than unsuccessful pairs. An experiment using artificial nests suggested that concealment from below the nest site and tree density in the nest patch were selected independently. I speculate that Dusky Flycatchers select nest patches that conceal parental movements from nest predators, and that fewer trees with dead branches may indicate the selection of higher tree or foliage vigor in occupied territories. The possibility of multiple selective factors and processes, differentially affecting the selection of nest-site, nest-patch, and territory-scale habitat is discussed.