A veil of fog lifts from the edge of San Francisco Bay, revealing a flock of shorebirds probing the soft mud for tiny invertebrates. Where they choose to feed tells us about the condition of their environment. This is valuable information for the planning and conservation action needed to address increased impacts from human activities.
|Western Sandpiper in breeding plumage. Photo by Tom Grey / www.tgreybirds.com.|
A Western Sandpiper suddenly secures a prey item and gulps it down before resuming her frantic search. She looks for productive mudflats that are teeming with juicy invertebrates. Protein-rich meals enable this tiny bird, with its high metabolic rate, to build up fat reserves to fuel her return trip to the Arctic to begin nesting. This underscores the importance to shorebirds of productive and plentiful shallow-water habitat—salt ponds and tidal mudflats—in San Francisco Bay.
On any given day, there are hundreds of thousands of shorebirds assessing the bay’s habitats and making decisions about where to feed and where to rest. By tracking their population size and where they congregate, we can make informed decisions about where to restore habitat and how much is necessary to support the million-plus shorebirds that depend on San Francisco Bay as a fueling station each year.
|Flocking sandpipers. Photo by Mike Baird.|
In former salt ponds that are now part of wildlife preserves on San Francisco Bay, resource managers can set water levels, salinities, and flow rates to produce abundant populations of invertebrates. Large numbers of shorebirds are attracted to abundant food in functioning salt-pond habitat. Monitoring birds can help scientists and managers learn which practices create the best habitat.
Wetland restoration projects aimed at increasing tidal marshlands (vital to both wildlife and human communities) often involve breaching levees to let tides rush in. The first habitat to form is mudflat, the preferred habitat of most shorebird species, but mudflats will eventually convert to vegetated marshes, less favored by shorebirds.
As part of a
Pacific Flyway-wide effort, PRBO researchers and citizen scientists have documented increases in numbers of shorebirds using the bay’s northern lobe, San Pablo Bay. This may be due to a recent surge of wetland restoration there, changing the mosaic of habitats. PRBO is working to evaluate the causes of these increases and what they teach us about how tidal wetland restoration can benefit shorebirds.
|Mudflats at low tide. Photo by Beck Cowles (Creative Commons).|
The need for this knowledge is growing more urgent, because shorebirds are also indicators of negative impacts of climate change. As sea levels rise, water becomes deeper over the mudflats, reducing shorebird habitat. Storms, predicted to become more severe and more frequent, may erode the most productive mudflats. The levees protecting critical shallow-water habitat may be overtopped. By keeping a close watch, we can detect declines in shorebird abundance in time to recommend management action.
The Western Sandpiper on the mudflat forages quickly, in a race against the clock. When the rising water becomes just a couple of inches deep, she must move elsewhere to feed or wait until the tide recedes. Will she and her young return next year and be counted by a researcher or citizen scientist? As climate change impacts sandpipers’ Arctic breeding grounds, and other changes affect their wintering grounds, the migrants in our estuary provide important measures of the health of their populations.
We too are racing against the clock, to understand how sea level rise might alter mudflats and the shorebird community and to mitigate the future impacts of climate change in San Francisco Bay. By putting our bird survey results into practice—sharing information with land stewards who manage and plan for shorebird habitats—PRBO’s science can help ensure that birds like the sandpiper will find enough high-quality habitat to fuel their migration and breeding.