Abstract
Biodiversity loss from agricultural intensification underscores the urgent need for science-based conservation strategies to enhance the value of agroecosystems for birds and other wildlife. California’s Central Valley, which has lost over 90% of its historical wetlands and currently is dominated by agriculture, still supports waterbird populations of continental importance. A better understanding of how waterbirds use available habitat is particularly needed in the Sacramento–San Joaquin Delta, an ecosystem under threat. From 2013 to 2015, we studied waterbird habitat associations in the Delta during fall migration and winter by conducting diurnal counts at random locations in key waterbird habitats throughout the Delta. Waterbird use of cover types (agricultural crops and managed wetlands) varied substantially among waterbird groups, by season, and among geographic subregions of the Delta. Overall, wetlands were particularly important to waterbirds in fall. In winter, wetlands and flooded rice and corn were important to many waterbird groups, and non-flooded corn and irrigated pasture to geese and cranes. The factors that influenced waterbird abundance and distribution also varied substantially among groups and differed at various geographic scales. In both seasons, most groups had a positive association at the field level with flooded ground and open water and a negative association with vegetation. Given the great uncertainty in the future extent and pace of habitat loss and degradation in the Delta, there is an urgency to prioritize conservation actions needed to maintain robust waterbird populations in this region. For the Delta to retain its importance to waterbirds, it will be necessary to maintain a mosaic of wetlands and wildlife-friendly crops that accounts for the value of the surrounding landscape. This includes restoring additional wetlands and maintaining corn, rice, alfalfa, and irrigated pasture, and ensuring that a substantial portion of corn and rice is flooded in winter.
Highlights
Management of fish and wildlife populations relies upon data generated from monitoring programs and analytical tools that use these data to inform decisions
Native to the headwaters of the Sacramento River basin in northern California, most winter-run spawning habitat was blocked by the construction of Shasta and Keswick dams on the Sacramento River, and currently the species exists as a single population that spawns in the mainstem Sacramento River near the terminus of fish passage
The use of annual smolt survival rates estimated from a mark–recapture model allows variation in detection probabilities to be accounted for, better characterizing the variances that inform the weighted mean approach to forecasting sn
Summary
Management of fish and wildlife populations relies upon data generated from monitoring programs and analytical tools that use these data to inform decisions. SAN FRANCISCO ESTUARY & WATERSHED SCIENCE because management actions can significantly affect population persistence, extinction risk, and the potential for recovery. One such imperiled species is Sacramento River winter-run Chinook Salmon (hereafter winter-run), which has been listed as Endangered under the Endangered Species Act (ESA) since 1994 (Fed Regist 1994). Winter-run persist in the Sacramento River outside of their historic range only because releases from Shasta Dam can be maintained at cool enough temperatures in most years to allow for successful spawning and egg incubation during the summer months (Fisher 1994; Yoshiyama et al 1998; Lindley et al 2007)
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