Nest-Site Characteristics of Hammond's and Pacific-Slope Flycatchers in Northwestern California

Abstract

Thirty nests of Hammond's (Empidonax hammondii) and 88 nests of Pacificslope (E. difficilis) Flycatchers were located in different-aged Douglas-fir (Pseudotsuga menziesii)/tanoak (Lithocarpus densiflorus) dominated forests at 12 study sites in northwestern California during the breeding seasons of 1984, 1985, 1987, and 1988. In contrast to Pacificslope Flycatchers, Hammond's used nest trees that averaged two to three times taller; placed nests three times higher and farther from the tree bole; used only live trees; placed nests only on smallto medium-diameter branches; situated nests in areas with higher foliage cover; and favored nest placement on the northeast and southwest sides of trees. Attributes of nesting habitat also differed between species among different stand development stages. Hammond's Flycatchers in old-growth and mature forests chose nest sites with more open canopy than that found at random sites. Pacific-slope Flycatchers in old-growth and mature forests nested at sites with a lower mid-canopy bole height. In young stands, Pacific-slope Flycatchers selected nest sites with large Douglas-firs and Pacific madrone (Arbutus menziesii) trees, higher shrub cover, and fewer medium-size Douglas-fir trees. Hammond's Flycatchers were not found in younger stands. We speculate that if old-growth Douglas-fir/tanoak forests are greatly reduced or eliminated in northwestern California, the density of breeding Hammond's Flycatcher will decrease substantially. However, Pacific-slope Flycatchers would probably be less affected by conversion of old-growth forests to younger-aged classes.