Roseate terns are among the shorebirds that rely on barrier islands, such as Cape Cod National Seashore, during their migrations/USFWS, Jorge Saliva

Editor's note: The following article was largely written by the staff at Cape Cod National Seashore.

Barrier islands play incredible roles for migrating shorebirds, offering them a place to stop, rest, and refuel. At Cape Cod National Seashore in Massachusetts, the beaches and marshes are important to common, least, and roseate terns and a number of other shorebird species during their migrations.

Even while some least terns and piping plovers are raising chicks on seashore beaches, roseate and common terns are beginning to gather, particularly on the barrier beaches at Hatches Harbor, Jeremy Point, and Coast Guard-Nauset. Terns, sometimes referred to as "sea swallows," are smaller than gulls and more graceful flyers, with forked tails and slender wings. After the nesting season, adult and fledgling terns disperse from their breeding grounds to "stage" on beaches and flats in southern New England before their 4,500-mile migration to South America.

During this staging period, the terns rest and feed in order to build body mass and fat reserves necessary to fuel their long migration south. This is a critical period for these terns and other staging and migrating shorebirds; it is important that disturbances to these birds while resting on beaches and flats are minimized. Vehicles, boat landings, kayaks, dogs, and pedestrians can startle, or flush staging birds, interrupting feeding and resting and forcing them to expend energy needed for migration.

Over the years, Cape Cod National Seashore staff has assisted the Massachusetts Audubon Coastal Waterbird Program and the U.S. Geological Survey in documenting the importance of seashore beaches to terns about to embark on their fall migration. From July through mid-October, researchers have counted many thousands of terns congregating at Hatches Harbor, Race Point, Coast Guard-Nauset Marsh, North Beach and South Beach/Monomoy beaches.Most terns observed are common terns, a Species of Special Concern in Massachusetts, and roseate terns, listed as endangered by the State and the U.S. Fish and Wildlife Service.

Based on counts of color-banded roseate terns, researchers estimate that 75 percent, or more, of the entire Northwest Atlantic Coast breeding population of roseate terns use Cape Cod National Seashore beaches and mudflats during their migration. In 2014, a detailed, multiagency, three-year study on the importance of the national seashore to staging roseate terns was initiated.

Cape Cod Superintendent George Price said he "encourages visitors and residents to observe this amazing phenomenon of thousands of birds utilizing national seashore beaches in preparation for their migration. It's important for people to witness this wonder of nature and share their experience with family and friends.Visitors are encouraged to enjoy terns and other shorebirds from a distance but should avoid disturbing these staging birds, since this period of resting and feeding is critical to their survival. Simply walking around flocks when you visit the seashore will help the birds tremendously."