It’s a sunbaked April morning in Ocean City, New Jersey, and from her perch atop the Ninth Street Bridge, Christina Davis scans the twisted limbs of trees growing from a small salt-marsh island below. The potent fragrance of low tide laces the briny spring air as Davis, a wading-bird biologist with New Jersey Fish and Wildlife, points to the nests among the gnarled branches.

This island, the shape of an elongated teardrop and so narrow you could toss a baseball across it, is the most productive wading-bird breeding site in the state, she says. Among the species that come here to reproduce, New Jersey lists seven as species of greatest conservation need, including black-crowned night herons, yellow-crowned night herons, great blue herons, and snowy egrets. But as of a few years ago, Davis adds, the busy breeding site has had a notable new arrival: white ibis (Eudocimus albus).

With long, slender bills; porcelain-white plumage; and tomato-red faces, white ibis are tropical birds on the move. In the early 20th century, in response to rising temperatures, white ibis expanded the northern extent of their range from Florida to South Carolina. Then, in the 1970s, they began nesting in Virginia. In 2020, the ibis made their latest leap. That year, biologists unexpectedly found four white ibis nests within the tussle of the Ocean City rookery. The discovery marked a roughly 1,300-kilometer (800-mile) move from the bird’s original home in Florida, and it left Davis stunned.

“When they returned the following year in bigger numbers, we wondered, ‘What’s going to happen?’” Davis says. “‘Will they boot everyone out?’” 

As we watch, a snowy egret shuffles on a cedar branch as a white ibis swoops in to land beside it. The branch sags heavily beneath them. In the background the bay looms large, making the rookery feel small and impermanent as Davis explains why the ibis’ arrival scared her.

Not long after the birds initially appeared in 2020, she says, the Ocean City rookery hosted more than 200 white ibis nests. More ibis were showing up each year. Davis worried that if that trend continued, with the newcomers presumably straining the rookery’s limited space and resources, the existing birds would suffer.

To monitor the health of the bird populations, Davis has been conducting annual surveys, heading out in a helicopter every spring for the past four years to track the number of adults, chicks, and nests of each species present. In 2023, she found so many white ibis chicks that the rookery’s surface seemed to roil.

Her four years of tracking, however, has revealed an unexpected surprise: Though the white ibis population has continued to grow, the populations of the other birds have remained remarkably stable. So far, competition between the different species seems not to be an issue. But the future of that ecological harmony is not guaranteed. 

Elsewhere around the world, other animals are also on the move. Scientists have documented bears, armadillos, wolves, lynx, frogs, butterflies, and other species shifting their ranges in response to rising temperatures.

“These species are doing exactly what we want them to do in the context of global anthropogenic change,” says José Ramírez-Garofalo, a graduate student studying species’ adaptive migrations at Rutgers University in New Jersey. “We want them to be able to adapt.”

Though many of the world’s plants and animals are following easily understandable escape routes—moving toward the poles or climbing to higher elevations—others are reacting in less predictable ways, which can pose a challenge for the biologists tasked with protecting them or managing their effects. 

Take, for example, the barred owl. Starting in the early 20th century, barred owls began expanding westward from eastern North America. Soon, the barred owls encroached into the territory of their close relative, the northern spotted owl. The two species live similar lifestyles, and they began competing for nesting space and food. The barred owl is a fierce competitor, and researchers with the United States Fish and Wildlife Service say barred owl encroachment, in conjunction with the loss of old-growth forest habitat, triggered a sharp decline in the northern spotted owl population. Today, the agency is being forced to consider how to control the barred owls’ impact and has proposed killing as many as 450,000 barred owls over the next three decades.

Davis is relieved New Jersey’s budding population of white ibis is not hurting the rookery’s other wading birds, though she’s unsure how long the current truce will last. A primary concern of Davis’s, which she shares with her New Jersey Fish and Wildlife colleagues, is sea level rise. As the state’s coastal marshes become inundated with water, islands like the one underlying the rookery will shrink. 

Recent government efforts to create new islands for nesting coastal birds are helping, but Davis says that may not be enough. If New Jersey’s average sea level rises by just 0.9 meters (3 feet), a figure well within the expected range for the area within the next 75 years, small salt-marsh islands like the Ocean City rookery will likely vanish.

Making the situation more difficult, Davis says, is that while state law protects individual bird species, it doesn’t protect their habitat. “That’s a huge hurdle for us,” Davis says. 

While nesting habitats shrink, New Jersey continues to welcome even more new species. In 2024, four years after the arrival of the first white ibis, the state documented its first roseate spoonbill, a species more familiar in Florida mangroves than mid-Atlantic marshes. Brown pelicans have started to migrate to New Jersey from southern latitudes, too, but have yet to nest. Davis expects that to change any year now.

One day in the not-so-distant future, Davis predicts that the mix of species in the Ocean City rookery will look wildly different than it does now. New species will establish themselves, while other species might head north or disappear. But she’s happy that, for now, everything appears to be working out. 

“They’re just incredible,” Davis says, turning her attention to a white ibis fluffing its silky white feathers over its egg-filled nest. “I hope they continue to be good neighbors.”