Tiny and easily overlooked among the hordes of more spectacular shorebirds streaming up and down the Atlantic Coast, the semipalmated sandpiper is suddenly standing out in the fragile ecological ballet that unfolds annually at the Delaware Bay.
The little brown bird, named because of its partially webbed feet, is providing new insight into the link scientists have drawn between the plummeting population of the more celebrated red knot sandpiper and dwindling number of horseshoe crab eggs on the New Jersey and Delaware shores.
A team of five researchers with New Jersey Audubon and a Dutch scientist, wrapping up a month of field work last week in the South American wintering grounds of the semipalmated sandpiper, announced that they have found evidence the species also is in serious decline — and likely for the same reason as the red knots.
In the 1980s, about 2 million semipalmated were counted by researchers on the 4,000-mile coastline of Suriname and neighboring French Guiana, where scientists say 85 percent of the world’s population of the bird winters annually. Last month, only 400,000 of the birds were found in aerial surveys by the New Jersey Audubon expedition.
“We had already found a 50 percent decline over 15 years by 2006. Now, this is a 70 to 80 percent decline since the survey in the 1980s. I think it’s alarming,” said David Mizrahi, the team leader.
The problem, he said, appears to be in the Delaware Bay — also the controversial source of the red knot’s troubles.
The area has been called the East Coast’s Serengeti because of the natural marvel that unfolds each spring. For eons, most of the Atlantic Coast population of horseshoe crabs have arrived at the bay to lay the eggs of a new generation.
In turn, millions of shorebirds migrating from southern wintering grounds land to feast on those eggs — a crucial meal as they continue their trek to northern breeding grounds.
“About 80 percent of the world’s population of red knots go through the Delaware Bay on their return north. About 60 percent of the world’s population of semipalmated sandpipers come through at the same time,” Mizrahi said.
“There just doesn’t seem to be a major change down in the wintering areas of either the red knot or the semipalmated sandpiper to explain a decline in either species. The Arctic breeding grounds of the red knot also have not changed … But what we do know is that there have been changes in the stopover area both birds share in North America,” he said.
New Jersey and Canadian biologists have insisted for years that a decline in horseshoe crab eggs in the Delaware Bay is causing the decline in red knots, which fly 10,000 miles from wintering grounds as far south as Tierra del Fuego. Where the birds once found 50,000 eggs per square meter, there are now 20,000.
Biologists also have concluded the red knots are arriving in Arctic breeding grounds too underweight to mate.
This is further evidence of the importance of an integrated, hemispheric approach to conserve “Canadian” birds like the Semipalmated Sandpiper. Protection of the shorebird’s Arctic breeding grounds is essential, but so too is working together on research and conservation initiatives along migratory pathways and at wintering habitats to ensure that we are addressing all the threats that these shorebirds face. The decline of this little, and little-known, bird is yet one more sign that we can’t keep stressing habitats without having large-scale and long-term effects on many interconnected species.