Bird Communities in Grazed and Ungrazed Oak-Pine Woodlands at the San Joaquin Experimental Range1

Ten years of spot-mapping censuses in grazed and ungrazed plots at the San Joaquin Experimental Range, Madera Co., California, indicate likely changes in abundance of several bird species. Data do not, however, indicate that any species is in jeopardy as a result of grazing in the foothill woodlands. Brown-headed cowbirds are probably more abundant in the woodlands with cattle than without cattle, but we have no evidence that cowbird nest parasitism is a threat to any host species. Finally, the European starling’s possible impact on native cavity-nesting species is uncertain, but we suspect it is significant for some species. In 1934, the USDA Forest Service purchased private ranchlands in foothill woodlands of the western Sierra Nevada to establish the San Joaquin Experimental Range (SJER). The stated objective of this acquisition was to undertake range research in California, which “...is most important for the stability of a large industry and for the maintenance of public values to be rendered by grazing lands” (Kotok 1933). Foremost among the public values of interest at the time were a viable livestock industry, sustainable water resources, and rangeland production. Other values were also recognized, including the rich wildlife communities that occur in the foothill woodlands. Publications based on studies of a wide variety of species in all vertebrate classes at SJER began to appear in the late 1930’s and early 1940’s (Duncan and Coon 1985). The primary objective of the present study was to evaluate spot mapping as a method to estimate the densities of breeding bird populations. Secondarily, we hoped to attain some insights into possible effects of long-term grazing on bird communities in oak-pine woodlands of the western Sierra Nevada. This second objective was possible only because a 32-ha parcel was set aside in 1934 and has been excluded from livestock grazing ever since. In this paper, we compare the breeding bird community in this ungrazed parcel with that in a grazed study area of equal size. Although the study lacks replication because only one ungrazed parcel was available, we nonetheless believe that some useful biological inferences can be drawn from the results.