Birders and conservationists have known of a link between declining numbers of Red Knots and overharvesting of horseshoe crabs in the Delaware Bay region for at least a decade. Now it appears that Semipalmated Sandpipers are having similar troubles, according to surveys conducted on the species's wintering grounds.
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.The research team sees the decline in Semipalmated Sandpipers as further confirmation that overharvesting of horseshoe crabs is at fault in the Red Knot population crash.
"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....
"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.
"The semipalmated sandpipers cement the underpinning that something more is in play here than just a problem isolated to the red knots," said Eric Stiles of the New Jersey Audubon expedition. "The semipalmated sandpipers don't winter in the same area as the red knot or breed in the same areas. They only share this one stopover area, the Delaware Bay, and they, too, are in decline."I am not at all surprised that a bird species other than Red Knot has been affected by the horseshoe crab situation in the Delaware Bay and elsewhere. In fact, it would not surprise me if other species like Ruddy Turnstone were having some trouble as well. The good news is that New Jersey's moratorium and restrictions in other states are in place before the reduction in horseshoe crab numbers became an existential threat to Semipalmated Sandpipers. Provided that those restrictions stay in place, the horseshoe crab population should rebound and the sandpiper population should stabilize.
The research team spent three weeks capturing 2,500 semipalmated sandpipers, taking blood and tissue samples and fitting them with identifying legbands. The data will be used in monitoring the semipalmated this spring as they return to the Delaware Bay.
"But in order to nail this all down, we must ultimately get to the breeding grounds as well to confirm that the problem is in the North American stopover," Mizrahi said. "We're following the model our colleagues in Canada and the New Jersey Division of Fish and Wildlife have already used on the red knots."
Unfortunately, the same cannot be said of the Red Knot, whose status is much more dire and will probably remain that way for at least the near future.