Waterfowl use of wetland habitats informs wetland restoration designs for multi-species benefits

Extensive global estuarine wetland losses have prompted intensive focus on restoration of these habitats. In California, substantial tracts of freshwater, brackish and tidal wetlands have been lost. Given the anthropogenic footprint of development and urbanization in this region, wetland restoration must rely on conversion of existing habitat types rather than adding new wetlands. These restorations can cause conflicts among stakeholders and species that win or lose depending on identified restoration priorities. Suisun Marsh on the San Francisco Bay Estuary is the largest brackish marsh on the US Pacific coast. To understand how conversion of brackish managed wetlands to tidal marsh would impact waterfowl populations and whether future tidal marsh restorations could provide suitable habitat for dabbling ducks, we examined waterfowl wetland use with a robust GPS-GSM tracking dataset (442,017 locations) from six dabbling duck species (N = 315). Managed wetlands, which comprise 47% of Suisun Marsh, were consistently and strongly selected by waterfowl over tidal marshes, with use similar to 98% across seasons and species. However, while use of tidal marsh (only 14% of Suisun Marsh) was generally <2%, almost half our ducks (similar to 44%) spent some time in this habitat and exhibited strong utilization of pond-like features. Ponds only comprise similar to 10% of this habitat but attracted 44% use (similar to 4.5 times greater than availability). Synthesis and applications. Managed wetlands were vital to dabbling ducks, but losses from conversion of these habitats may be partially mitigated by incorporating pond features that are more attractive to waterfowl, and likely to offer multi-species benefits, into tidal marsh restoration designs. While waterfowl are presently a common taxon, previously seen calamitous population declines can be avoided through informed ecosystem-based management that promotes species richness, biodiversity and helps 'keep common species common'.