Response of Waterbirds to Salt Pond Enhancements and Island Creation in the San Francisco Bay

Historically, San Francisco Bay supported the largest salt pond complex on the Pacific coast of North America, and these areas have been used by large numbers of migrating and wintering waterbirds for more than a century. In 2003, salt ponds in the South San Francisco Bay were purchased with a goal of restoring 50-90% of the 6100 ha of former salt ponds to replace lost tidal marsh habitats. However, a major challenge for the restoration project has been maintaining the abundance of non-breeding waterbirds in a smaller footprint of managed ponds. Thus, in 2009-2010, Pond SF2 was enhanced with 30 islands of two different shapes and water control structures that provided muted tidal flows with shallow water depths predicted to benefit waterbirds. To assess how non-breeding waterbirds responded to these enhancements, a spatial grid (50 m x 50 m) was used to survey SF2 weekly from October to May 2010-2012, and examine waterbird use. Of the 262,932 non-breeding waterbirds observed, only 12-15% used the islands depending on tide. Island size, shape, or both predicted the presence or relative abundance of some foraging guilds, whereas island slope, perimeter, and distance to mudflat did not improve the model\u27s predictions of relative guild abundances. Results indicated that waterbirds were attracted to areas with shallow water depths; however, the constructed islands were not used by a large number of waterbirds

Waterbird monitoring and habitat association modeling to inform tidal marsh restoration in an urbanized estuary

The San Francisco Bay (SFB), like many other urbanized estuaries, is a critical wintering and stop-over area for migratory waterbirds. More than a million wintering waterbirds annually rely on a mosaic of natural and managed habitats in SFB, including former salt ponds. The South Bay Salt Pond Restoration Project plans restore 50 to 90% of a 6,100 hectare former salt production pond complex to tidal marsh, while maintaining the rest as foraging and roosting areas for migratory birds. Since 2002, we have evaluated migratory waterbird use of pre- and post-restoration salt ponds in south SFB. Our approach has been to use monthly surveys, applied studies and modeling to evaluate avian response to this changing habitat. Trend analyses indicate that overall waterbird numbers have nearly doubled across the complex from 2003-2014. Dabbling ducks increased significantly during initial phases of the project, while diving ducks, small and medium shorebird abundances declined initially, but rebounded in recent years. We modeled relationships between abundances of multiple species and habitat characteristics at both landscape and micro-scales. Modeling results suggest that the importance of different habitat characteristics varies among waterbird guilds. For example, foraging diving duck abundances were higher in deep, un-breached ponds, located close to the edge of SFB, while foraging small shorebirds predominated in shallow, breached ponds containing islands. Our research highlights important habitat characteristics both within and across wetland areas, and provides a unique opportunity to guide future management and restoration decisions for multiple species across large landscapes in SFB and other urbanized estuaries