Ruddy turnstones and semipalmated sandpipers are among shorebirds who congregate near the shoreline at Kimbles Beach in Middle Township, New Jersey. Each spring, shorebirds migrating from South America to the Arctic stop on the sands of Delaware Bay to feast on horseshoe crab eggs. Jacqueline Larma/Associated Press

As we mark Earth Day this weekend, I want to consider the plight of shorebirds. Shorebirds are a convenient grouping of bird families that generally include wading birds that frequent the shorelines of oceans, lakes and flowing water.

Shorebirds include sandpipers, plovers, oystercatchers, avocets, stilts and phalaropes, as well as other birds like the ibisbill and painted snipes that don’t occur in North America. Most shorebirds are long-distance migrants, spending the northern winter as far south as Tierra del Fuego in Chile.

We have some nesting species of shorebirds in Maine like killdeer, spotted sandpiper, Wilson’s snipe and American woodcock. However, most shorebirds breed at high latitudes on the Arctic tundra. Most shorebirds on the list of Maine birds are passage migrants; we see them briefly in the spring and fall as they pass through to and from the tundra.

Shorebird migration differs in an important way from landbird migration. On migration, landbirds may end a migratory leg anywhere along their migration route. However, shorebirds tend to use traditional stop-over areas. Their migrations are therefore often point-to-point routes.

These stop-over areas are food-rich areas that permit shorebirds to fatten to replace their fuel stores so they can continue their migration. For brief periods of time, most individuals of some species can be found at a single site. Examples include Delaware Bay in late May, when red knots stop to feed on horseshoe crab eggs, and the upper Bay of Fundy, where semipalmated sandpipers gather in August and September to feed on small crustaceans in the expansive intertidal mudflats. Obviously, protecting these stop-over areas is of paramount importance.

The Western Hemisphere Shorebird Reserve Network was established with the cooperation of biologists throughout North America, Central America, South America, and islands of the Caribbean. This network has no legislative power but serves to educate politicians, environmental managers and naturalists about important stop-over areas for shorebirds in the Western Hemisphere. Nineteen countries are participating in the network, and 115 stop-over areas are identified as critically important.

A recent article in the journal “Ornithological Applications” provides an alarming assessment of shorebird populations in the Western Hemisphere. Paul Smith and nine co-authors (a mix of Canadian and American biologists) considered the population status of 28 shorebird species.

The study relied on shorebird abundance data in the fall from 1980 to 2019. Several monitoring programs (the International Shorebird Survey and two Canadian shorebird surveys) provided the bulk of the data.

The authors found that 26 of the 28 shorebird species for which sufficient data was available showed declines over the four decades. Nineteen species showed uniformly negative declines across all survey areas.

This pattern is distressing enough but is exacerbated by the finding that the rate of decline is accelerating. Comparing the current three-generation period (10 to 23 years depending on the species) with the previous three-generation period showed that 18 species have stronger declines in the more recent period.

Over half of the species analyzed had declines of 50% or more over the study period. This rate of decline qualifies these species as threatened under current international guidelines.

Staging areas between North Carolina and Nova Scotia show the strongest declines of shorebird abundance. Staging areas along the Gulf Coast and in the center of North America show negative but less severe declines.

What species seem to be most in danger? Red knots and Hudsonian godwits head the list. Both species lost 90% of their numbers over the study period. Others with precipitous declines are short-billed dowitchers, long-billed dowitchers, dunlin, lesser yellowlegs, whimbrel, stilt sandpiper and ruddy turnstone. The only two species showing an increase are marbled godwit and willet.

What are we to do? Interventions require targeted efforts based on the biology and migration route of each species. The success of the American oystercatcher project gives hope. Recovery efforts were started in 2010, and by 2019, a 23% increase in oystercatchers was realized.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu