Migratory birds love New York Harbor islands, but humans are forcing them out

New York Harbor is a dating hot spot for migratory birds.

About 40 islands dot the waters around New York City, but only a handful become a hotbed for bird breeding from the end of April to mid-July. These isles are typically off-limits to humans, but every May, New York City Audubon gets special permission from the city parks department to traverse the islands to count the nests of 10 wading bird species — and this year, Gothamist tagged along.

The annual nesting survey for the NYC Harbor Herons Program is more than just counting birds. Audubon scientists use the numbers to gauge the effectiveness of conservation efforts. These wading birds — or waders, as the field researchers call them — are characterized by long necks, long bills and long legs that allow them to catch food in shallow water.

They fill the desolate patches of harbor land with tightly packed reed-spun nests in bushes, in trees or right on the beach. They’re guarded overhead by a cacophony of adult birds screeching, vomiting fish and defecating. By taking tallies at their breeding grounds, scientists can also track adult and baby populations — and the potential threats to their survival.

While this year’s count looks promising with 1,398 active nests — a 25% increase over 2022’s numbers — scientists have witnessed alarming declines in nine of the 10 wading bird species they track in New York City’s waters. Rainbow-breasted glossy ibises and black-crowned night herons are faring the worst, while great egrets are the only birds in the Harbor Herons survey that are not in decline.

“While that may seem like a lot of nests for New York Harbor, these counts are nearly half of what was in the harbor in the mid 1990s,” said Dustin Partridge, director of conservation and science at NYC Audubon. He said they have noticed a downward trend since 2010 — reversing gains obtained through past conservation efforts.

The 2023 spring survey also detected a decrease in the number of wader species visiting the harbor. Last year, a total of nine species came to the island to mate. This year, only seven species were present on the six islands still used for breeding.

NYC Audubon is now investigating the declines in New York Harbor by conducting a full analysis of the data set that goes all the way back to 1985, the first year of the official annual survey. In the early 2000s, when the harbor’s peak population was recorded, waders converged on 15 of these islands every spring.

But rising sea levels and predators such as rats and raccoons have caused the birds to abandon more than half their colonial nesting sites.

“This is amazing real estate on an island in New York City, and you would expect that to be developed by now,” Partridge said. “One of the reasons this has been set aside is exactly because of the importance of this island as a reference for these herons and egrets.”

How the Harbor Herons survey happens

After jumping off a speed boat in Jamaica Bay at low tide in late May, Partridge and a team of half-dozen ecologists waded in hip-deep water toward the shore, carrying a car’s rear-view mirror attached to a 10-foot pole. The contraption is used to look into and count nests on high branches as well as the eggs and chicks inside.

The harbor islands they visit vary in size and layout. Some of these breeding sanctuaries are as small as 450 square feet, roughly the size of a subway car plopped into the East River — and the 10 wading species share the spaces with other types of birds. One isle was crowded with orange-faced double-crested cormorants, a species that has been on the rise in the harbor and is only tracked secondarily to see its influence on wading birds.

The breeding habitats also include the flat marshy patches in Jamaica Bay, which are covered in brush with nests stacked like many tiers of an afternoon tea stand. The land is so soggy, a footstep can be knee-deep.

“A lot of times you have a bunch of different species nesting together,” said Shannon Curley, a migratory bird researcher at the Cornell Lab of Ornithology. “You’ll have great egrets on top, and then black-crowned night heron and snowy egrets below them and then glossy ibis on the bottom.”

Stepping foot on these islands can disturb the birds and raise the chances of the animals eventually abandoning the habitats. So, the scientists do their work quickly, spending as little time on the islands as possible. In the future, Partridge said they would prefer to use drones to avoid human presence on the islands altogether.

As soon as they reached the shore, Tod Winston, a former survey leader, drew a map in the sand with his index finger, describing the parts of the island. The six conservationists then set off in different directions.

Curley, the survey leader and data collector, juggled a memo pad in her left hand and a pen in her right. She moved amid the counters, listening for the nest counts to come in from the rest of the team.

“I have a snowy egret nest with two eggs and one chick,” one person called out. In her palm-sized steno pad, Curley wrote down everything.

What’s threatening the waterbird isles?

Amid the signs of bustling life, there was also a death toll.

Curley took note of numerous deceased birds caught up in fishing lines, or chicks that had perished from ingesting the plastic that litters all the islands.

Plastic is a major pollutant in the harbor. NY/NJ Baykeeper, an environmental advocacy group, estimated at least 165 million bits of plastic are in the New York-New Jersey Harbor. That’s more than 1,000 plastic particles per acre.

The harbor birds also face other dangers. Avian flu continues to plague birds globally, though no evidence of the bird flu was found on the islands. Predators are another danger, and many of them are urban animals that thrive due to human activity.

The field scientists found rat holes burrowed underneath the ground nests and raccoon scat near a baby bird carcass. These animals, which most likely swam from parks on the mainland, often break open eggs. Their presence is one of the key factors causing birds to abandon their longtime colonies.

“Within about a year of raccoons being spotted on an island, the colony abandons,” Partridge said. “That’s happened repeatedly over the years we’ve done this survey.”

Unauthorized humans are another factor. The scientists record the telltale signs of trespassing: beer bottles, graffiti, charred wood and abandoned Jet Skis.

“A lot of these birds, especially colonial nesting waterbirds, are very sensitive to having human presence on the island,” Curley said. “It’s going to prevent the birds from returning to this habitat.”

She noted how the perimeter of one island was once full of nests. This year the birds had all crowded inland, away from the shore and potential intruders. The island’s interior foliage was covered with chalky white guano.

Rising sea levels are a perpetual and growing danger for waterbird isles.

Winston said that over the past decade, the team has found drowned nestlings, whose numbers have been increasing with more frequent and severe storms.

“These low-lying islands in Jamaica Bay are amazing, but that’s also why they’re so vulnerable,” Partridge said. “They’re so close to the high tide lines. They’re so close to predators.”

Some islands no longer have any birds to count, but the volunteer conservationists visit them anyway – hoping to see signs of a return or if the birds will use them as a secondary feeding ground.

With fewer than half the harbor islands being used for breeding, Partridge said discovery of a recolonized habitat would be a victory for conservation efforts. For the last three years of surveys, the islands have experienced their slowest breeding seasons.

“Last year, our surveys were disheartening because they were the lowest number of wading bird nests ever recorded in the harbor,” Partridge said. The number of nests in the harbor was 1,116.

Once birds abandon an island, they don’t return. Sometimes, they even cause overcrowding on islands with existing colonies. Since 1982, when the Audubon started recording its observations, it has never seen birds return to an island they have fled from.

Last year’s survey noted the abandonment of one of the largest and most diverse island colonies in NY Harbor: Subway Island, where the A train runs without stopping on its way to and from Broad Channel.

“Every time we lose an island, we’re losing birds,” Partridge said.. “The birds that we do have are concentrated on the few islands that are left, and that increases their risk to predation, flooding, disturbance.”

What else this year’s annual survey found

Partridge believes that most of Subway Island’s breeding populations just moved to neighboring island of Little Egg Marsh — where the wading bird population had tripled this year. He said that could be a bad sign for the future.

“Unfortunately, this island is close to shore and people visit frequently, which may result in colony abandonment or death of the chicks due to disturbance,” Partridge said.

Three species weren’t even spotted this year: cattle egrets, tricolored herons and green herons. Last year, these species had no nests or just a few nests spotted the year before. Three other species had fewer than 10 nests: little blue herons, yellow-crowned night herons and great blue herons.

The number of active nests belonging to great egrets, the one species in the Harbor Herons Program that isn’t facing decline, swelled by about one-third year over year.

Two other species bounced back compared to 2022: black-crowned night herons increased their active nests by 36% and glossy ibises added 66%. But those rebounds weren’t enough to counteract their long-standing decline.

“Year to year there is a natural variation in the number of nests, and then there are overall population trends,” Partridge said. Overall, these two wading birds’ populations have declined more than 60% over the last two decades from their peak in the early 2000s.

Black-crowned night heron populations are dwindling across the Northeast, and the species is listed as endangered, threatened or of special concern in surrounding states.

“These species are really having a hard time everywhere,” Partridge said. “Black-crowned night heron is not yet a listed [endangered] species in New York state, but its population in New York is disappearing as fast, or faster, than in nearby states.”

Avian declines are a nationwide trend. The National Audubon estimated in 2019 that the U.S. has 3 billion fewer birds now than it did in 1970. That’s more than 1 in 4 birds vanishing from U.S. habitats over the last half-century.