Avian community structure in a large urban park: Controls of local richness and diversity

Abstract

This study compared avifaunal richness and diversity at five ponds in Golden Gate Park, San Francisco, California. The objectives of the study were to: (1) determine interpond differences in avian community structure and composition; (2) evaluate avian-habitat relationships; (3) use these data to develop recommendations for enhancing avian habitats within urban refuges. Of eight environmental variables measured, three correlated highly with the over-all use of pond areas by birds; the width of buffer between the pond and park boundary; general habitat structure within the buffer zone (i.e. peripheral habitat structure); local habitat structure around the pond. Aquatic birds, unlike transitional or upland species, were not affected by either the width of buffer or peripheral habitat structure; rather, pond size largely dictated the number and diversity of aquatic bird species. Overall richness and diversity of birds were higher at the more natural and centrally located ponds, whereas abundance and biomass were greatest at the most unnatural and least isolated site. Avifaunal differences among sites were attributed to two factors: (1) the level of urban-related disturbance, which in turn is a function of the width of buffer and the structure of peripheral habitats: (2) the availability of species-specific habitat requirements, which depends on local habitat conditions. Interpond variation in avifaunal richness and diversity in Golden Gate Park was striking, and underscores the influence of man dictating local avifaunal differences within urban parks. Recommendations for designing and maintaining pond habitats to enrich bird communities in urban parks are: (1) construct ponds (preferably >1 ha) as far as possible from adjacent urban development, and maintain a complex mosaic of vegetation within the buffer zone surrounding the pond; (2) establish shrubby vegetation interspersed with bare ground and trees along the shoreline; (3) provide irregular shoreline shapes (i.e. high edge); (4) maintain overhanging vegetation or low artificial perches (e.g. flooded posts) in or near the water; (5) provide islands; (6) maintain standing dead trees (especially flooded).