The red-eyed and feisty black-crowned night herons are in danger of disappearing from New York City Harbor, ecologists say.
The nocturnal creature is the city’s most common wading bird, and the Big Apple has historically been home to the largest population in the Northeast. But the noisy, belligerent bird’s local population dropped 55% between 2000 and 2022, when researchers counted roughly 470 active nests.
In a report released June 3, researchers with the New York City Bird Alliance said the data suggest the black-crowned night heron could vanish from New York City as soon as 2037.
“Black-crowned night herons are the quintessential New Yorker,” said Dustin Partridge, the alliance’s director of conservation and science. “They are these cool-looking birds that like to stay out late.”
The declining number of nests could also suggest a larger problem.
The stocky, monochromatic bird is what ecologists call an indicator species, which means that if it’s struggling, there’s something amiss within the ecosystem.
“ Black-crowned night herons are just not another bird species in the harbor. These are an indicator species telling us something about environmental health,” said Shannon Curley, an avian ecologist and lecturer at Stony Brook University. “Their decline may be an early indicator, an early warning sign that there's other additional ecological pressures that are building in places that people are not always visually seeing.”
Ornithologists are not certain what might be causing the decline. But their theories include predators, human activity and pollution.
The birds congregate in dense, noisy colonies and favor islands and wetlands like marshes, ponds and swamps. But the location of their woody, foot-wide nests makes them susceptible to predators such as raccoons, which reach the islands by swimming or taking the subway tracks that cross some of the islands. The nests are located on shrubs and in trees, and can yield between three and five bluish-green eggs each year on average.
Raccoons eat eggs and chicks under the cover of night while the adults are out hunting for food.
Curley said the presence of raccoons will cause birds to abandon an island altogether for nesting, reducing the size of available habitat and increasing competition among birds for space.
Around 2022, during the height of mating season, ecologists found the once-bustling bird colonies of Subway Island in Jamaica Bay completely deserted, likely due to raccoons using the A train tracks that traverse the island’s length.
“Raccoons use the subway tracks that run through the islands in Jamaica Bay as a land bridge to get there,” Curley said. “Raccoons can decimate entire colonies and cause them to abandon habitats.”
Human activity, like boat traffic and development, affects all bird species. Bird colonies congregate over small wetlands, sometimes hardly an acre in size.
“They're just like New Yorkers. They will make do with what they can find,” Partridge said. “These smaller wetlands that are around New York Harbor, both in New York and New Jersey, are incredibly important.”
The most worrisome theory for the declining population is the presence of contaminants in the environment, the alliance said.
Despite improved water quality over recent decades as a result of the Clean Water Act, new pollutants such as microplastics and PFAS — also known as forever chemicals — that remain in the environment, and possibly even raw sewage from combined sewer overflow, could be a major factor in the decline. According to the alliance, black-crowned night herons are very sensitive to pollution.
Partridge and Curley’s report, published in the journal Conservation Science and Practice, is meant to raise the alarm on the black-crowned night heron’s decline.
“We made this discovery before it's too late, which means that our conservation efforts can save these birds,” Partridge said. “We won't let these birds go extinct in the next 10 years.”
The next steps for ornithologists are to identify the cause, which could include testing feathers and eggs for the presence of toxins.
Identifying the reason for the decline is intrinsic to creating an effective conservation plan, whether it's environmental remediation to reduce pollutants, deterrents for predators or legal avenues such as listing the species as endangered or stricter policies to protect wetlands. The species is listed as threatened in Pennsylvania and endangered in New Jersey.
The alliance said it is urging New York state’s Department of Environmental Conservation to also list the bird as threatened or endangered.
“If these birds disappear from the harbor, we're probably going to start losing some of the nesting islands because other birds are going to get the cue that something's going wrong,” Partridge said. “These birds are charismatic and if that bird disappears, we're losing that connection with nature and fewer people are going to care or be invested in trying to make positive change throughout New York City.”
The environmental conservation department said in a statement that in 2024 it began proposing updates to the state’s list of animals it considers endangered, threatened or of special concern. It said it would use all available data to make recommendations for the list of birds it adds to its list. It added that the decline noted by the alliance is supported by other data.
Black-crowned night herons inhabit New York City from March through October. During the winter, the birds fly to the southern portion of the United States and the Gulf of Mexico.
At the height of mating season during the spring, the herons build nests out of twigs in trees and bushes in colonies of dozens, among several other species. They mate for life.
The noisy avians are very tenacious about defending their nests, including bullying other heron species, attacking with their beaks, defecating or regurgitating on human intruders and creating an unpleasant, ear-splitting cacophony of harsh songs.
While they have a near-perfect hatch rate among their eggs, only about half of the fledglings survive to adulthood.
“ I love how feisty these nestlings are in the nest. They're like little dinosaurs,” Curley said. “They’ll chase you with their beak and try to go after you. I really appreciate that about them.”