出版社：San Francisco Bay-Delta Science Consortium and the John Muir Institute of the Environment
摘要：http://escholarship.org/uc/item/63j6s1tb Populations of many species of birds are declining worldwide from habitat loss and degradation and the effects of contamination, disease, and alien species. Effects have been great in California’s Central Valley from the loss of over 90% of its historical wetland and riparian habitats. Conservation initiatives at various geographic scales have ranged from protecting and restoring habitats or ecosystems for broad suites of species to ones identifying individual declining and vulnerable taxa and spurring actions to halt or reverse their population declines. In taking the first approach, the Central Valley Joint Venture initially focused on restoring habitats and populations of wintering and breeding waterfowl but currently promotes the conservation of all birds. This joint venture is setting population and habitat objectives for seven taxonomic or habitat bird groups, but to date little attention has been paid to at-risk species of particular conservation concern. We identified 38 at-risk species, subspecies, or distinct populations of birds that warrant heightened conservation efforts in the Central Valley. At-risk birds are unevenly distributed among subregions and habitat types in this valley, but most face the primary threat of habitat loss and degradation. The treatment of at-risk species varies greatly among the seven bird groups considered by the joint venture, and, overall, conservation objectives are not addressed specifically for 50% of the region’s at-risk taxa, though some surely benefit from objectives set for other groups. To adequately treat at-risk species, we recommend a framework for setting conservation objectives that evaluates assumptions about limiting factors, considers objectives already set for threatened and endangered species, assesses whether objectives set for other groups or focal species meet the needs of at-risk species lacking such objectives, establishes objectives for at-risk species for habitats or seasons not currently considered, and highlights information gaps to be filled to effectively set new or refined objectives.
