Wetlands are critical for shorebirds, but which ones in western North America are most important? Until recently, this information was lacking. In the late 1980s, PRBO embarked on a project to count shorebirds in all the western United States wetlands. We expected San Francisco Bay, because of its large size, to prove very important but had no idea how many birds it might hold--or how to find out. If we could develop a method to document shorebird abundance in San Francisco Bay, we could likely cover the other western wetlands as well.
|Complete coverage of the bay's shoreline required thousands of individual person-hours. Photo by Miko Ruhlen.|
We decided to follow the protocol used for shorebird counts at Bolinas Lagoon, where 6-8 people cover 3 areas on a moderately high, rising tide. But San Francisco Bay would need coverage of 171 areas!
Biologists from PRBO collectively spent 8 months prior to the survey visiting all the areas to determine how to access and cover them most effectively. We recruited 183 volunteers and assigned them to teams including at least one experienced birder. Each counter received an information packet and survey forms. For our first bay-wide count, in April 1988, we covered the North Bay one day and South Bay the next.
Some participants had tens of thousands of shorebirds to count. Small sandpipers were particularly difficult to tell apart, especially when in large mixed flocks. The counting techniques we provided helped participants meet these challenges. Some habitat was difficult to traverse, and often there were tidal channels to cross: we hoped we had assigned the most agile jumpers to these areas!
In the end, the skilled volunteers prevailed, tallying a remarkable 838,000 shorebirds of 28 species. Twelve additional San Francisco Bay counts followed. We found that the bay holds more migrating and wintering shorebirds than any other wetland on the U.S. West Coast south of Alaska. Consequently, the Western Hemisphere Shorebird Reserve Network designated San Francisco Bay a site of hemispheric importance.
From our first bay surveys we also recognized the value of salt ponds as feeding and roosting habitat. PRBO initiated further studies to examine the salt pond's relative importance in the Bay ecosystem. Most recently, we used the count results to estimate potential negative effects of non-native cordgrass (Spartina alterniflora) on the extent of mudflats and the number of shorebirds that can forage there.
We are enormously grateful to the hundreds of volunteers who trudged through mud, lept over sloughs, and committed to a standardized protocol to provide the first-ever bay-wide census of shorebirds using San Francisco Bay. Their efforts are guiding today's restoration priorities across this vital ecosystem.