Assateague Island and the International Shorebird Survey, 2013–2024

American oystercatchers, a willet and a marbled godwit near the surf during an International Shorebird Survey on Assateague Island. NPS.

A survey turns 50

The International Shorebird Survey (ISS), organised by Manomet Conservation Sciences, began in 1974 as a volunteer effort to understand shorebird populations and migration, and to find the places shorebirds rely on as they migrate.

It started with surveys at under 100 sites. By 2023 it had over 1,300 survey sites across North, Central and South America, and more than 100,000 surveys had been carried out. 2024 marked the survey's 50th anniversary, a milestone for the hundreds of people who have contributed to it.

Park staff and a Scientists in Parks intern survey for shorebirds from a jetty near the Ocean City Inlet (survey plot 1). NPS.

How Assateague takes part

Assateague Island National Seashore, in Maryland, has taken part since 2013. The park set up five survey plots of similar length and width along the island's coast. Staff and interns drive each plot, counting shorebirds as well as possible disturbances: people, vehicles and dogs. Assateague is home to a great many kinds of birds, but only shorebirds are counted for the ISS.

Seen most often: piping plover, American oystercatcher, sanderling, willet, ruddy turnstone, semipalmated plover, black-bellied plover, semipalmated sandpiper, least sandpiper and whimbrel.

Rarer finds: Wilson's plover, American golden plover, short-billed dowitcher and marbled godwit, among others.

When the counts happen

• Early years: mainly April and May, for spring migration, and September and October, for fall migration.
• 2020: a hard year — the pandemic made it difficult to survey as a group.
• Recent years: more surveys, added in spring and summer and as late as November, to catch the end of fall migration, when red knots and dunlins can still be seen. Surveys now run 2 to 3 times a month.

What the counts show

Since 2013, the surveys at Assateague have counted 309,331 shorebirds, an average of 25,778 a year. Around 15 shorebird species are usually recorded, but some years have found as many as 19 using the island as a stopover on migration.

Shorebirds counted, and surveys conducted, each year during International Shorebird Surveys on Assateague Island, 2013–2024. NPS.

Two birds of special interest

The ISS also tracks two shorebirds of particular concern at Assateague: the piping plover and the red knot. Both are federally listed as threatened. Maryland lists the piping plover as endangered, and Assateague is its only breeding site in the state.

A piping plover on Assateague Island during fall migration, 2024. NPS.

More red knots have been seen in recent years, likely helped by extending the surveys later into the fall, including November.

Piping plovers and red knots observed each year during International Shorebird Surveys on Assateague Island, 2013–2024. NPS.

Why it matters

The ISS remains a useful way to monitor shorebird numbers and migration at Assateague, and to compare them with regional and hemisphere-wide trends.

All ISS data are public, on eBird and through Manomet Conservation Sciences, whose mapping tools let anyone explore migration trends by species, place, month or year. Researchers have used the data to study single species and regional trends, and a recent paper documented accelerating declines in North America's shorebirds (Smith and others, 2023, in The Condor: https://academic.oup.com/condor/article/125/2/duad003/7031074). More on the survey and its maps: https://www.manomet.org/project/international-shorebird-survey/

Sources

• Emily Paciotta, Biological Science Technician, with park contact Lindsay Ries, Biologist, "Contributions to the International Shorebird Survey at Assateague Island, MD", Assateague Island National Seashore, National Park Service. https://www.nps.gov/articles/000/contributions-to-the-international-shorebird-survey-at-assateague-island-md.htm
• Rewritten in hubnx's own words.