Abundance and Diversity of Resident and Wintering Birds in Undisturbed California Oak Woodland

Anne Y. Polyakov, University of California at Berkeley, Department of Environmental Science, Policy, and Management

William D. Tietje, University of California at Berkeley, Department of Environmental Science, Policy, and Management

California oak woodlands are located in the center of a major north-south migratory passage and, in addition to being home for populations of resident birds, millions of migratory birds seek winter refuge and maintain breeding grounds in these areas. Due to increasingly pervasive and intense drought and fires that are burning more frequently and intensely than ever before, information on bird use of oak woodland for wintering and breeding is especially important today. As part of a long-term study of the population dynamics and habitat relationships of small terrestrial vertebrates in an undisturbed oak woodland in coastal-central California, observers conducted bird point count surveys at 86 sites during winter 1997-1999 and spring 1997-2003. They recorded 41,510 detections of 84 bird species. Species evenness (aka relative abundance; an indication of ecosystem stability) was higher for resident species (0.67) than for migratory species (0.45) in winter; there was no difference in spring. In both winter and spring, species richness and overall abundance were higher for residents than for migratory birds. The most abundant winter resident species were the oak titmouse (Baeolophus inornatus), Bewick’s wren (Thryomanes bewickii), and American robin (Turdus migratorius), while the most abundant migrants were the dark-eyed junco (Junco hyemalis), hermit thrush (Catharus guttatus), and the ruby-crowned kinglet (Regulus calendula). In the spring, the most abundant resident species were the oak titmouse and Western scrub jay (Aphelocoma californica), while the most abundant migratory species were dark-eyed junco, ash-throated flycatcher (Myiarchus cinerascens) and violet-green swallow (Tachycineta thalassina). The high number and diversity of both resident and migratory species that utilize California oak woodland demonstrates its importance as a critical bird wintering area and breeding grounds.