Patterns of Breeding Songbird Diversity and Occurrence in Riparian Habitats of the Eastern Sierra Nevada

We determined several vegetation and environmental features that predicted breeding bird species diversity and focal species occurrence in riparian habitats across three watersheds of the eastern Sierra Nevada bioregion, California. Conducting point counts and associated vegetation assessments at 480 individual riparian points between 1998 and 2000 permitted us to investigate bird and habitat relationships at different spatial scales ranging from the entire study area to specific habitat types within climate zones falling along elevational and latitudinal gradients. In particular, Aspen and Black Willow habitats were positively correlated with breeding species diversity, as were tree species richness, width of the riparian zone and elevation. Habitat models predicting the occurrence of Yellow Warblers (Dendroica petechia), Warbling Vireos (Vireo gilvus), Song Sparrows (Melospiza melodia) and Black-headed Grosbeaks (Pheucticus melanocephalus) accurately classified 65-83% of test sites, and highlighted the importance of habitat features including aspen (Populus tremuloides) cover, riparian width, grass cover, tree species richness and tree height. This effort is the first of its kind for the region, and results can be applied to local and statewide riparian management and restoration efforts. determined habitat and landscape characteristics that influence western bird populations at large spatial scales in California's Klamath bioregion (Alexander 1999), the Northern Rocky Mountains (Hutto and Young 1999) and the Columbia Plateau (Holmes and Ge upel 2000). Managers can use results derived from these approaches to determine which vegetative features to manage for regionally (Hutto and Young 1999). It is sometimes inappropriate to extrapolate bird habitat relationships derived from a small study area (Wiens 1981; Knopf and Samson 1994), and large-scale conservation efforts are rarely orchestrated from the management unit level where research and monitoring is conducted. Therefore, state and bioregional riparian songbird and habitat conservation efforts (e.g. RHJV 2000) need data derived from larger scale projects to fulfill some of their more general objectives. There is also justification for taking a finer scale approach. Our study area, and the eastern Sierra in general, is made up of riparian drainages of various geophysical settings and structures, and it is therefore difficult to make generalizations about vegetation across the entire study area (Kondolf et al. 1987; Harris et al. 1987). Also, bird habitat relationships derived from an area covering numerous habitat types and geomorphologic regions may not be meaningful or applicable to local management efforts. By bracketing our study sites within climate zones and habitat types, we take some of this variation into consideration and are able to offer suggestions to managers at more local scales. Previous western studies, two of which occurred near or within our study area, have taken this smaller scale approach, incorporating one river drainage, or a 21 in California Riparian Systems: Processes and Floodplain Management, Ecology, and Restoration (2003), P. M. Faber (Ed.), Riparian Habitat and Floodplains Conference Proceedings, Riparian Habitat Joint Venture, Sacramento, CA.