Surveys over the past decade show significant declines in the numbers of horseshoe crabs and shorebirds. The sanderling population alone has decreased an alarming 80 percent in the past decade. Suspected causes for the decline are the use of pesticides in the winter grounds and loss of coastal wetlands along migration routes.

Working with an international team of scientists, biologists in Delaware and New Jersey are tracking shorebird movements and population trends. This information may help clarify factors affecting the birds.

Loss of habitat at stopover sites, dredging of wetlands, and constant competition with humans for prime coastline increase pressure on the shorebirds. Human disturbance at staging areas may reduce feeding time. Only fat, healthy birds survive the final trip to the arctic breeding grounds. THe short arctic summers mean time to raise only one small brood. Low reproductive rates make it harder for shorebirds to sustain healthy populations.

Scientists continue to study the relationship between shorebirds and horseshoe crabs. They want to learn more about the birds' dependency on crab eggs for food. Although these trends seem to be related, evidence suggests that shorebird feeding has no impact on the horseshoe crab population.