Vegetation associations of birds wintering in a California oak woodland

Conditions in wintering areas can have persistent effects throughout the year for bird populations. Most studies, however, are conducted during the breeding season and the non-breeding ecology of many species remains poorly understood. We assessed vegetation associations of birds wintering in a diverse, well-structured oak woodland in coastal-central California. We calculated density estimates for 20 bird species and examined correlations between bird densities and vegetation characteristics as described by a principal components analysis. Ruby-crowned Kinglets (Regulus calendula) and Hutton's Vireos (Vireo huttoni) were positively associated with vegetation characteristic of dense, floristically diverse woodland with abundant coast live oak (Quercus agrifolia) cover and a structurally complex understory. Conversely, White-breasted Nuthatches (Sitta carolinensis) and Western Bluebirds (Sialia mexicana) were negatively correlated with dense woodland and occurred at the highest densities on plots with large widely spaced blue oaks (Q. douglasii) and a sparse understory. Thirteen of the remaining 16 species were more abundant in dense woodland patches, but these relationships were not statistically significant. Our results are in agreement with those of previous studies and suggest that evergreen oak trees and a dense understory provide key resources (e.g., cover and food) for some bird species during the winter. However, areas with large widely spaced deciduous oaks are important habitats for other species. We therefore suggest that dense patches of live oaks and shrubs should be retained, but a mosaic of dense and sparse woodland is necessary to accommodate the entire suite of oak-woodland birds. Las condiciones en áreas invernantes pueden tener efectos persistentes a través del año en poblaciones de aves. Sin embargo, la mayoría de los estudios se han conducido durante la temporada reproductiva y, para muchas aves, la ecología fuera de dicha época ha sido pobremente examinada. Nosotros determinamos las asociaciones de vegetación relacionadas con aves invernantes, en un bosque bien estructurado de roble en la parte costanera central de California. Calculamos la densidad de 20 especies de aves y examinamos la correlación entre densidad y características de la vegetación como descrita por un análisis de componente principal. Regulus calendura y Vireo huttoni, fueron positivamente asociados a vegetación diversa y densa con una gran abundancia de robles vivos (