The past few decades have brought unprecedented change to the bottom of the world—and Antarctica's penguins may be paying the price.

A recent, preliminary census of the chinstrap penguins on the islands along the Antarctic Peninsula has revealed a sharp and alarming decline in the birds’ numbers, with some colonies experiencing as much as 77 percent drop since the 1970s. Though the findings have yet to be published in a peer-reviewed scientific journal, they fall in line with the results of several other studies documenting similar drops in other polar species.

Experts also have yet to confirm the direct cause of the drop-off. But based on previous research in the region, the researchers behind the project suspect the likely culprit is climate change, which continues to bump up Southern Ocean temperatures and strip local ecosystems of their sea ice.

“Our best guess on why … is climate change, which we know is hitting the Antarctic Peninsula region harder than … practically anywhere else in the world except the Arctic,” team member Noah Strycker, an ornithologist at Stony Brook University, tells Aryn Baker at TIME. The report arrives on the heels of a sobering announcement from the World Meteorological Organization last week that said Antarctica had hit a record high temperature of nearly 65 degrees Fahrenheit.

Considered some of the most iconic Antarctic mainstays, chinstrap penguins have spent millennia adapting to the world’s southern pole. Standing just a couple feet tall, the blubbery birds are accomplished hunters at sea and expert mountaineers on the icy terrain. Evolution has tailored them exquisitely to their surroundings—and even the slightest changes can imperil their livelihood.

Chinstrap penguins, then, serve as a sort of ecosystem barometer: Their suffering is a litmus test for troubles to come.

“This shows something in the marine ecology is broken, or has drastically changed since the 1970s,” Strycker tells Jonathan Watts at the Guardian.

Strycker and his colleagues conducted the census as a part of an Antarctic Greenpeace expedition that ran from January 5 to February 8, deploying drones and handheld clickers to tabulate the number of chinstrap breeding pairs along the frigid continent’s northwest. All 32 colonies surveyed on Elephant Island—a famous chinstrap outpost—had dwindled, yielding a nearly 60 percent drop in the island’s total population compared to 1971, when more than 100,000 breeding pairs roamed its shores.

Assessments of the nearby islands of Livingston and Low are telling a similar story, the researchers told the Guardian. A formal report of the team’s efforts is forthcoming, but the main message is unlikely to change: The chinstraps are in trouble.

A likely driver of the birds’ issues is the alarming disappearance of their primary prey source, krill. These tiny crustaceans have decreased by as much as 80 percent in some Antarctic seas, reports Jason Bittel for National Geographic. Though scientists are still sussing out the factors killing the krill, warming waters and ocean acidification both likely play a role. These declines don’t just hurt chinstraps: As a key player in countless food chains, krill sustain many other species as well, including fish, seals and whales.

Increased rainfall in the region could also be endangering young chicks, who are prone to deadly hypothermia during these weather aberrations, P. Dee Boersma, a penguin expert at the University of Washington who wasn’t involved in the project, says in an interview with National Geographic.

Not all penguin species are likely to suffer the same fate. Quickly replacing the waning chinstraps are hardy gentoos, known for their flexible foraging and breeding habits. As climate change pushes more sensitive species out of the regions, these plucky, orange-beaked birds are engineering a form of “gentoofication,” Strycker tells TIME.

But for the most part, the outlook is not rosy—and the world needs to act fast. Greenpeace has beseeched the United Nations to commit to protecting 30 percent of the world’s oceans by 2030. As Greenpeace Oceans campaigner Frida Bengtsson tells Stuart McDill at Reuters, “I think we stand to lose much of what we love.”