Shorebird Migration

As a group, shorebirds undertake some of the most spectacular of long-distance migrations of any North American birds. Nearly two-thirds of the species that breed in North America journey from their arctic nesting grounds to winter in Central and South America, and then return to the Arctic the following spring. Many species traverse more than 15,000 miles in this annual circuit. Some fly at altitudes exceeding 10,000 feet and achieve cruising speeds approaching 50 mph. From sightings of marked individuals, we know that at least some birds on nonstop flights cover nearly 2,000 miles in less than two days. Hudsonian Godwits may fly 8,000 miles nonstop between breeding and wintering areas, unless brief stopovers are made at as-yet-undiscovered spots somewhere in South America. The surprising migration feats of Sanderlings were discovered only recently by ornithologist Pete Myers. Their hitherto unsuspected circumnavigation of the Americas each year follows a route east across the top of North America and down the Atlantic coast in the autumn to their wintering grounds in Chile and Peru, and back north in the spring through the western United States to their arctic breeding grounds.

Although more than 20 million shorebirds migrate through the United States to the Arctic each year, Myers and his colleagues have captured the attention of the ornithological and conservation communities with their recent discovery that the long-term survival of even abundant species may be in jeopardy. Their studies show that Sanderlings, Ruddy Turnstones, Red Knots, Dunlins, and White-rumped, Baird's, Stilt, Western, and Semipalmated Sandpipers form enormous concentrations at several key staging areas along their migration route. Each of these spots is critical for successful migration of these species, providing superabundant food resources that enable the birds to quickly replenish their energy reserves and continue on. In North America, five such sites support more than a million shorebirds annually: Alaska's Copper River Delta, Washington's Gray's Harbor, eastern Canada's Bay of Fundy, Kansas' Cheyenne Bottoms, and the beaches of Delaware Bay in New Jersey and Delaware. More than 80 percent of the entire North American population of some species may join ranks at any of these key locations; virtually all Western Sandpipers and Dunlins use the Copper River site. Other similarly vital locations have been identified throughout the Americas. These few critical staging areas underpin the entire migration system of New World shorebirds. As Myers points out, such enormous concentrations dependent upon so few widely spaced locales breaks the usual link between a species' abundance and its immunity to extinction.

The series of critical stopover sites is typified by Delaware Bay. The arrival and departure of 500,000 to 1,500,000 shorebirds within a span of three to four weeks is synchronized with the annual breeding cycle of the bay's enormous population of horseshoe crabs, for it is the eggs of the crabs that supply the energy required by the birds to complete their spring journey to the Arctic. Each evening, after day-long feasting on crab eggs, the birds move east to roost in tidal marshes and on the outer beaches of the Atlantic coast. Coastal and wetland development have forced the birds into ever smaller foraging and roosting sites as the number of suitable areas has dwindled. On high-tide nights, more than 100,000 shorebirds may be packed into a few hundred yards of beach.

Fortunately, efforts are now under way to link the staging sites connecting wintering and breeding areas into a system of sister reserves. Shorebird biologists, backed by the World Wildlife Fund - U.S., the International Association of Fish and Wildlife Agencies, and the National Audubon Society are working toward establishment of these critical reserves throughout the Americas. Success hinges on persuading local, regional, and national governments that such a system is not only desirable but absolutely necessary to ensure the survival of migratory shorebirds. As a first step, in May of 1986 the governors of New Jersey and Delaware mandated the lower estuary of Delaware Bay as a reserve for shorebird conservation.

SEE: Spacing of Wintering Shorebirds; Shorebird Feeding; Sandpipers, Social Systems, and Territoriality; Birds and the Law; Migration.

Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.