Nest-Site Habitat of Cavity-Nesting Birds at the San Joaquin Experimental Range

Detailed information about the nesting habitats of birds, including those needed for successful nesting, can provide a better understanding of the ecological factors that permit coexistence of different species and may aid in conservation efforts. From 1989 through 1994, we studied the nesting habitat of secondary cavity-nesting birds in oak woodlands at the San Joaquin Experimental Range, Madera County, CA. We measured habitat surrounding nests and examined similarities and differences in nesting habitat used by eight species to evaluate overlap in nesting habitat use and possible competition. Nesting habitat of Bewick’s Wrens (Thryomanes bewickii) was unique among the species studied. Their nests were the lowest and located in the densest habitat on the steepest slopes where interior live oaks (Quercus wislizenii) were abundant. Nesting habitat was similar among European Starlings (Sturnus vulgaris), Western Bluebirds (Sialia mexicana), and Violet-green Swallows (Tachycineta bicolor). These species all nested in open areas with the highest density of blue oaks (Quercus douglasii), the lowest densities of live oaks and snags, and the lowest basal area of trees. Nests of White-breasted Nuthatches (Sitta carolinensis) were similar to the above three species, differing only in being lower compared to nests of European Starlings. Ash-throated Flycatcher (Myiarchus cinerascens) nesting habitat was characterized by dense stands of trees with a high density of live oaks and snags. Oak Titmouse (Baeolophus inornatus) nests were low and located in high-density stands of live oaks on steep slopes. House Wrens (Troglodytes aedon) nested in dense stands of trees. Successful Ash-throated Flycatcher and Oak Titmouse nests had higher basal area of live trees compared to unsuccessful nests and, compared to other species, habitat surrounding their nests had high basal area. European Starling nests were highest, and nests located high in trees had higher nest survival. Consequently, these three species tended to select nest sites in habitats where they had higher nest success. We recommend management activities that maintain habitat diversity, including areas that differ in tree species composition and density, to promote species diversity.