SOUTH LUBEC — The Nature Conservancy announced Tuesday it bought what it described as one of Maine’s most important shorebird staging areas, a coastal sand beach in South Lubec.

The property is a 3,500-foot straight sand and gravel spit that runs parallel to the shore about a mile west of Quoddy Head, the easternmost point in the United States.

The conservancy bought the land for $40,000 from a Connecticut couple who had planned once to make a trailer park at the site. The purchase protects the gravel bar, associated salt marshes and the wide mud flats exposed during low tides.

The purchase was funded in part by a grant from the National Fish and Wildlife Foundation.

The area is a stop-over for migrating shorebirds traveling south in late summer from nesting areas in subarctic and arctic Canada. Semi-palmated sandpipers, semi-palmated plovers, black-bellied plovers, ruddy turnstones, sanderlings and other species congregate on the mud flats to eat insects, worms and other invertebrates.

The birds may stay for a week, increasing their weight as much as 50 percent to complete flights as long as 4,000 miles.

Shorebird migrations are different from those of other birds because they are funneled through a few key spots, called staging sites, where an abundance of food awaits. The migration presents challenges for conservation because loss or degradation of a single staging site could jeopardize large portions of shorebird populations, according to conservancy officials.

The mud flats are one link in a hemisphere-wide chain of wetlands considered critical for shorebirds and ensures that such birds will be able to roost and rest, undisturbed, during high tides and between feedings.

The site was identified as part of the North American Waterfowl Management Plan, an international effort headed in Maine by the Department of Inland Fisheries and Wildlife to protect critical waterfowl habitat.