Conceptual Framework and Ecological Considerations for the Study of Birds in Oak Woodlands

The distributions and abundances of birds within oak woodland communities of California are the results of geologic events leading to the formation of the Mediterranean-type ecosystem, and of more recent anthropogenic impacts that have altered the landscape. These human-wrought disturbances to oak woodlands likely are affecting population parameters and distributions of birds throughout California. Because little is known of bird-habitat relationships in oak communities, however, the actual effects of these land-use practices on birds are unknown. Here we present a framework for the study of birds in the oak woodlands of California. The principal objective of this framework is to outline aspects of bird biology, ecology and behavior that must be addressed before assessments of habitat quality can be made. Assessments of habitat quality require that population numbers, reproduction rates, and survival rates be monitored. Further, bird habitats must be studied to determine site characteristics of areas that birds actually use within oak woodlands. Determination of specific patterns of resource use entails intensive study of bird activities. Collection of all of these data requires extensive field work to determine temporal and spatial patterns of habitat and resource use. There are no shortcuts for obtaining this information. naturalists (e.g., Grinnell and Miller 1944, Leopold 1951, Miller 1951) provided valuable species accounts based on their observations. The information presented by these naturalists was generally in the form of qualitative descriptions of species' distributions and habitat associations. These data are of insufficient detail, however, to allow resource managers to assess habitat quality or to predict the effects of environmental change on bird population parameters. Further, Muick and Bartolome (1985) found few recent studies of bird-habitat relationships in oak woodlands. Consequently, a research program is required to study bird-habitat relationships in oak woodlands that provides information in sufficient detail to allow assessments of habitat quality and predictions of the effects of habitat change on birds. The purpose of this paper is to present a general framework for the study of birds in oak woodlands. Our primary objective is to outline aspects of bird biology and ecology that researchers must study to provide the baseline information required by managers to determine habitat quality for birds. We begin this framework by suggesting a scenario to describe distributional patterns of birds within oak woodlands. We use the discussion as a basis for explaining ecological and behavioral relationships of birds to their environments, and we conclude by presenting a methodology for the study of birds in oak woodlands.