Seabirds evolved about 60 million years ago, as Earth’s continents drifted toward their current positions and modern oceans took shape. They spread across thousands of undisturbed islands in the widening seas. And as flying dinosaurs and giant omnivorous sea reptiles died out, seabirds also started filling an ecological niche as ecosystem engineers.

They distribute nutrients, in the form of guano, that’s beneficial to plankton, seagrass and coral reefs, which, in turn, nurtures fish populations that are eaten by seabirds and marine mammals in a cycle that forms a biological carbon pump. The stronger the pump, the more carbon dioxide it pushes into seabed sediment storage.

Seabird colonies of almost unimaginable size likely persisted through eons of profound climate shifts and the geological upheavals of colliding continents, playing a profound role in the ocean carbon cycle. But even in their most far-flung island realms, they were quickly decimated by humans who colonized and industrialized the planet during the past 200 years.

By some estimates, the overall global seabird population has dropped by as much as 90 percent during that time, with a decline of 70 percent just since 1950. Seabirds are the most threatened group of birds and one of the most endangered groups of species, according to the International Union for the Conservation of Nature. Of 346 seabird species, 97 are globally threatened, and another 35 are listed as near-threatened. Almost half of all seabird species are known or suspected to be experiencing population declines.

Most of the damage has been from invasive predators—humans themselves, and the rats, cats, dogs and pigs they brought along as they exploited island after island. After millions of years of predator-free evolution, the birds didn’t recognize the new species as threats. They were particularly vulnerable because they don’t breed as prolifically as many terrestrial birds, and spend a long time nurturing their flightless young on land. 

There was also direct human predation on an industrial scale, with the harvest of seabird eggs for food, their guano as fertilizer and the birds themselves to render for oil, along with seals, sea lions and whales, or as the unwanted bycatch of commercial fishing boats. On the Farallon Islands near San Francisco, home to the largest single seabird nesting colony in the United States, the murre population dropped from 400,000 to 60,000 in just a few decades during the gold rush, as people harvested up to half a million eggs per year.

Today the Farallon Islands are protected as part of a marine sanctuary and the nesting seabird colonies are recovering, helping to sustain the surrounding marine ecosystem, including great white sharks, apex predators that sometimes feed on the population of northern fur seals that have returned to the islands since they were protected. Rhinoceros auklets, related to puffins, have also returned and more than 20 endangered and threatened species—birds, reptiles, insects, marine mammals and even sea turtles—live on and and around the islands.

Related: Ocean Protection Around Hawaiian Islands Boosts Far-Flung ‘Ahi Populations

The Comeback Has Already Started

And there are hundreds of other seabird restoration projects around the world showing signs of success, said Dena Spatz, a scientist with Pacific Rim Conservation, a nonprofit that focuses on ecosystem repairs. Spatz was lead author of an April 10 study in the Proceedings National Academy of Sciences that compiled data from 851 restoration projects in 36 countries targeting 138 species of seabirds over the past 70 years. 

The new study focused on efforts to actively bring back bird populations, including social attraction methods, like using decoys, as well as direct translocation of young birds to new sites free of invasive predators. In more than 75 percent of the restorations, targeted species visited the sites and started breeding within 2 years. 

“It’s an incredible success story,” she said. “A lot of seabirds come back without any intervention… But that’s not always the case all the time.”

Some populations of seabirds are tiny and widely dispersed across distant islands, and a few of them have blinked out, she said. That makes it hard for the bird populations to get back to historic breeding levels without help.

“That’s where active restoration, moving things from one place to another, becomes super critical,” she said.

Restoring seabirds could bolster ocean ecosystems and their ability to draw down carbon dioxide, said Hans-Otto Pörtner, a climate scientist at the Alfred Wegener Institute in Germany, who recently co-authored a research paper in Science that spells out the the connections between biodiversity, ecosystem protection and climate stabilization.

In addition to direct CO2 emissions from burning fossil fuels and other industrial processes, the disruption of ecosystems and biodiversity declines have also significantly contributed to rising atmospheric greenhouse concentrations that are heating up the planet, he said.

“Biodiversity loss contributes to climate change through loss of wild species and biomass,” the paper concluded. “This reduces carbon stocks and sink capacity in natural and managed ecosystems, increasing emissions.”

The resulting warming disturbs ecosystems in a vicious circle that worsens “the unprecedented loss of biodiversity already caused by human-induced habitat degradation, overexploitation of natural resources, and pollution,” he and his co-authors wrote in the Science paper. 

Adding continued biodiversity loss and habitat decline with projections for greenhouse gas emissions, Earth is on a path to heat up to near 3 degrees Celsius by 2100, and that won’t change unless humans proceed on the planet in a way that “allows biodiversity to thrive, and which incorporates a strengthening of the natural pathways of carbon binding and storage,” Pörtner said.

Related: ‘Rewilding’ Parts of the Planet Could Have Big Climate Benefits

Can Assisted Migration Help?

The new seabird restoration study is part of a growing canon that documents thousands of various nature restoration projects on every continent, according to Restor, a nonprofit network building a global restoration database. 

Restoring seabirds can help turnaround the declines in biodiversity and carbon sequestration, Spatz said, describing some of the translocation research pioneered by scientists in New Zealand that will help similar efforts elsewhere. The idea of moving birds physically from one place to another to restore populations is part of a growing effort of assisted migration, which some scientists think will be critical as climate change impacts intensify. For seabirds, it’s done most with species that have evolved to return to the place they are born, she said.

“There’s this amazing biological response in birds like petrels, shearwaters, albatross and some puffins,” she said. “They’re born on an island, they fledge, they go to sea from anywhere between one and eight years, depending on the species and then go back to the place where they were born.”

Relocation of the chicks is timed so they imprint on their new home in the way they normally would at the site where they hatched, she said. 

“It’s a huge endeavor to do this stuff. But it works when you do it, right,” she said. “What’s amazing is, once these birds come as fluffy chicks to a restoration site, they’re raised by people, but they don’t imprint on us. That’s just the way seabirds are, so that’s not a worry. Then they get feathers, and they fly on their own out to sea. And when it’s time to breed, they go to the restoration site instead of the place they were born.”

On Hawai’i, she said, scientists have been relocating albatross and petrel chicks from some of the low-lying Northwest Hawaiian Islands, where there are huge bird colonies, but some nesting grounds are already being swamped by rising seas.

“It’s not a future threat,” she said. “It’s a current threat. Those chicks probably wouldn’t have survived anyway if we hadn’t taken them.”

Let Ecosystems Flourish to Benefit the Climate 

Scaling up nature restoration and conservation efforts, including with seabirds, is absolutely critical to preventing a worst-case global warming outcome, said Bernie Tershy, an ecology and evolutionary biology researcher at the University of California Santa Cruz.

“A key part of that is pulling pollutants out of the atmosphere, right? So if you’re going to do that, one could argue that the best way to do that is to plant a whole bunch of the fastest growing trees over the most area possible,” said Tershy, who was not an author of the new seabird study but has worked on similar research.

But that would be like putting all your climate eggs in one basket, he said, describing risks, like wildfires and insect infestations that could quickly wipe out such monocultures before they have any climate benefits. A better approach is a diversified investment spread across ecosystems that suck carbon out of the atmosphere. 

“It’s also totally the cheapest way because it’s a passive thing,” he said. “All you have to do is protect these natural areas and manage them well. They’ll soak up a ton of carbon and they’ll do it in a way that is incredibly resilient.”

But you can’t just focus on a single species, he added.

“You need a bunch of different plant species,” he said. “And you need insect grazers and fertilizer-producing species. You need small mammal seed dispersers and you need the birds that disperse seeds and the fertilizers they produce that nurture the seeds. You need all that biodiversity to maintain resilient ecosystems that pull carbon out of the atmosphere.”