Counting Purple Sandpipers on the Coast of Maine, 2001–2024

Long-billed and plump, the Purple Sandpiper stands out against the blue Atlantic as it probes Acadia National Park's rocky shore for blue mussels, crustaceans and other marine invertebrates. Late-winter wind doesn't seem to bother it. Few shorebirds stay on Acadia's coast through the stormy winter, and the Purple Sandpiper has the northernmost winter range of any shorebird in the world.

It breeds farther north still, inside the Arctic Circle — in coastal Greenland, northwestern Europe and Canada's northernmost islands — laying eggs in a simple nest on the ground, where the males care for the young. The downy chicks can leave the nest and feed themselves almost as soon as they hatch. When they first fly is not known; it is presumed to be at about three weeks.

Hardy, but not immune

Shorebirds are among the most threatened groups of birds in the world because of human activity: habitat destruction, overharvesting of their prey, and climate-driven changes in their prey's life cycles all make life harder.

Purple Sandpiper numbers have fallen in Scotland and Belgium, where changing weather led some birds to winter farther west than usual, following plentiful food — leaving some shores emptier than expected while others stayed busy. That raises a question for North America: are populations truly declining, or are birds simply moving?

Hard birds to count

Until the early 2000s, North American Purple Sandpipers were little studied, partly because they prefer to winter on Maine's remote offshore islands, out of reach of most birders and of the Christmas Bird Counts.

• 2001–2004. Glen H. Mittelhauser, Lindsay Tudor and Bruce Connery carried out the first systematic survey of Acadia's coastline for the species, part of a wider statewide assessment. They suspected their count was low — many birds used stretches of coast that could not be seen from boats, and storms and poor light may have hidden others — yet Maine clearly held far more Purple Sandpipers than Christmas Bird Count figures had suggested.
• 2014–2017. A second survey of the Maine coast found a steep fall, suggesting a 49% decline over the preceding decade. If the decline continues at that rate, the species could soon face local extinction.
• 2023–2024. Using the earlier surveys as a baseline, a new statewide count was coordinated by Elliot Johnston, a postdoctoral scientist with the Maine Natural History Observatory, with support from the Maine Outdoor Heritage Fund. Johnston, Mittelhauser and biologists from the Maine Department of Inland Fisheries and Wildlife retraced the historical routes, including in Acadia, to give resource managers current numbers to guide protection.

The work is demanding. Maine's coast has approximately 4,500 islands and more than 3,500 miles of irregular shoreline across many habitats. Offshore waters mostly stay free of ice in winter, but the weather is changeable and can turn brutally cold and windy, so crews use boats of different sizes depending on conditions. They follow the mainland shore and circle islands as closely as safety allows, counting the small birds among the rocks — and even with several observers, some estimation is needed to reach a sound count.

Why the count matters

Surveys suggest Maine may host over a third of the western Atlantic's wintering Purple Sandpipers, which makes Acadia and the Maine coast an essential refuge. The birds are also a window on the Gulf of Maine ecosystem, which is harder to monitor directly. Even if the sandpipers can cope with a wide range of conditions, their prey may not: blue mussels and other mollusks are sensitive to warming seas and ocean acidification, so fewer sandpipers may mean fewer of the animals they eat. Surveys like this one help managers understand what the species needs and make decisions about the ecosystem around it — and the birds themselves remain a delight to watch.

Sources

Based on "Research Brief: Surveying Purple Sandpipers through the Decades," published by the National Park Service, Acadia National Park; rewritten in hubnx's own words.

• The brief spells one researcher's name two ways; this page uses Mittelhauser, as in the brief's first mention.
• The brief's photographs, credited to C. Schmitt of Schoodic Institute, are not reproduced.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.