Slow and Steady: Gradual Drawdown of Private Wetlands Supports Shorebirds During Northbound Migration

The Grasslands Ecological Area is the largest contiguous wetland complex in California's Central Valley and is a stronghold for hundreds of thousands of waterbirds. Primarily managed for waterfowl habitat and forage production, landowners of these privately owned seasonal wetlands in the Grassland Ecological Area typically flood the wetlands in the fall and dewater them the following spring in February and March. These wetlands support large populations of nonbreeding shorebirds and other waterbirds in winter. When the number of migratory shorebirds using the region peaks in mid-April, landowners have already dewatered most wetlands. The mismatch in the timing of available habitat and the habitat needs of migrating shorebirds contributes to the observed deficit of shorebird habitat in the Central Valley in spring. Working with private landowners, we developed and tested a wetland management practice designed to increase the amount of shallow-water habitat available to shorebirds in April by delaying the drawdown and reducing water levels more slowly (gradual drawdown) relative to the traditional management practice. On average, we found that wetlands managed with gradual drawdown provided over twice as much shorebird habitat, contributing up to 26% of the overall shorebird habitat objective for the Central Valley. Wetlands managed with gradual drawdown supported up to 21 times more migratory shorebirds during peak migration and a greater number of shorebird species than traditionally managed wetlands. Our results demonstrate the potential of working with private landowners to implement small changes in wetland management that can have a large impact in meeting regional conservation objectives for migratory shorebirds.