Documenting the return of the terns to Poplar Island

Each year, seabirds migrating along the Atlantic Flyway pass through the Chesapeake Bay region looking for sandy beaches to call their home. Once here, the water-loving birds will make their nests, lay eggs and welcome new chicks into the world.

But between human recreation on beaches, new development and increased coastal flooding, these birds increasingly struggle to find safe habitat on and around the Bay.

Two species of concern—the least and common tern—face particular challenges in the area.

In Maryland, common terns are classified as endangered and least terns are classified as threatened, and both species have shown a steady decline since the mid-2000s all along the Atlantic coast. The birds prefer open beaches with sparse vegetation, preferably free from human disturbances and large mammals who prey on their young.

There have been a number of efforts to provide terns with more habitat in Maryland—from inland bay restoration to man-made nesting rafts—but one of the most notable is the work being done on Poplar Island. Located in the Chesapeake Bay in Talbot County, Maryland, Poplar Island is a three-mile island that was once a fully functioning community with over 100 residents. When sea levels began to rise and erosion took its course, Poplar Island became uninhabitable and residents were forced to move to the mainland. By 1990, the island was a mere five acres.

To salvage this land, island restoration began in 2001—relocating dredged material from the waterways that flow into the Port of Baltimore to the remnants of the island. Now, Poplar serves as an environmental restoration site for a variety of threatened wildlife. Wildlife biologists from a collection of federal and state partners maintain habitat conditions and monitor visitors to the island.

Of the 38 waterbird species that nest on the Poplar Island, least and common terns are some of the most vulnerable. Compared to other species of emphasis—including American black ducks, snowy egrets, cattle egrets, double-crested cormorants and osprey—terns have had especially variable success when hatching and fledging (when young develop wings large enough for flight) at the island.

“This year we have been facing high levels of pressure from avian predators such as great blue herons and crowned night herons,” explains Jeffery Sullivan, a biologist in the U.S. Geological Survey’s Eastern Ecological Science Center.

In 2013, the United States Geological Survey (USGS) launched a project to monitor nesting sites and tern chicks more closely on Poplar Island. With the help of volunteers, USGS scientists such as Sullivan temporarily capture tern chicks to mark them with special bands. Plastic field readable (PFR) bands that differentiate each bird are placed on one of the hatchling’s legs, while metal bands provided by USGS’s Bird Banding Lab are placed on the other. With the help of high-power spotting scopes (small, portable telescopes that magnify objects), USGS scientists are able to identify and read the bird’s band from far distances to keep track of how young terns are progressing and which sites they travel to on Poplar Island.

“The most surprising thing is the flexibility [of terns] to follow ideal habitats across the island,” said Sullivan. According to the USGS scientist, when returning north in the spring, terns will venture to different areas of the island with freshly placed sand stockpiles, rather than nest at sites they’ve previously been to.

Through this project, USGS scientists have gathered useful data on how tern colonies perform each year. While the pairs of nesting common terms have fluctuated between 2002 and 2018, with a low of 86 and high of 915, 307 pairs were estimated in 2018. Least terns, who have had as low as 12 nesting pairs, had their highest estimate with 330 pairs in 2018.

In an effort to identify how common terns use global habitat, USGS scientists created a growth-friendly tern harness to attach to 18 adult and 24 juvenile common terns during their 2021 migration. These harnesses contain radio-transmitters that allow scientists from the USGS Eastern Ecological Science Center to track their migration journey.

One of the harnessed common terns was spotted by a community scientist in Aruba—over 1,850 miles away from where it was originally tagged. These radio-transmitter tags gather detections from receivers but since there were no receivers in the region of the sighting, the scientist’s report was especially helpful.

The wildlife management that takes place on Poplar Island is dependent on interagency collaboration. While USGS monitors terns, the United States Fish and Wildlife Service (USFWS) works to improve habitat for the bird. For example, the organization makes sure that the beach’s vegetation is sparse enough for the terns to lay their eggs in the soft sand, which would otherwise be taken over by wild plants and grasses. In general, USFWS enhances the underwater grasses and wetlands that are in and around the Poplar Island, which improves habitat conditions for multiple species.

The Poplar Island Environmental Restoration Project, as the restoration effort is officially called, will come to an end in 2043 and the island will then be turned over to the State of Maryland.

Luckily, Poplar Island is only the beginning of island habitat restoration in the Chesapeake Bay. Just south of Poplar—in western Dorchester County—you’ll find early construction of the Mid-Bay Island Ecosystem Restoration Project or “Mid-Bay.” Similar to the work being done on Poplar Island, this project is repurposing dredged material to rebuild the remains of the separate James and Barren Islands, providing hundreds of acres of wetland and terrestrial habitat for fish, reptiles, amphibians, small mammals and birds.

Until then, the work at Poplar Island will continue to serve tern populations and expand habitat options for seabirds in the Chesapeake Bay.