Located at the edge of a treacherous stretch of ocean and surrounded by sea ice even in most summers, the Danger Islands on the Antarctic Peninsula’s northern tip are among Antarctica’s most inhospitable and aptly named areas. Because the trek there is so arduous, scientists have rarely set foot on the islands and didn’t know much about the penguins that had been anecdotally reported living on the rocky outcrops in the Weddell Sea.

Until recently, that is. In 2014, Stony Brook University ecologist Heather Lynch and NASA Goddard Flight Center scientist Mathew Schwaller used algorithms to search NASA’s Landsat satellite images of Antarctica for signs of penguins. On the Danger Islands, they saw light brown stains on the islands’ white ice surface: it was guano, a sign of a large grouping of penguins, which they verified with higher resolution imagery. But the true size of the colonies was impossible to know until Lynch and a group of scientists finally sailed there the following year to get a closer look.

They were amazed to find that the islands are home to a “supercolony” of Adelie penguins tallied at about 1.5 million individuals or 750,000 nesting pairs. The discovery, reported in a new study in the journal Scientific Reports, includes the third- and fourth-largest individual Adelie penguin colonies in the world on two of the islands.

“They are by far the most well-studied of all penguin species, which is one of the reasons why this new finding was so surprising,” said Lynch, who is coprincipal investigator of the research.

The discovery underscores the importance of protecting areas like the Danger Islands where penguins still thrive, especially as climate change alters sea ice patterns and the ocean conditions that support krill, the tiny crustaceans that polar predators love to eat. In some areas of the Southern Ocean, krill populations are also declining, even as they are still fished commercially.

To count all the penguins, Lynch and her team spent about a month on the Danger Islands, which lie past the southern tip of South America, surveying some areas themselves. They also used unmanned aerial vehicles (UAVs) to examine the landscape more systematically, flying drones a minimum of 82ft (25m) in the air so as not to disturb the penguins. Hanumant Singh, professor of electrical and computer engineering at Northeastern University, led the effort to piece together the photos into larger images and train an algorithm to recognize penguin nests in them. They compared the software’s work to their manual counts on four islands – Brash, Earle, Beagle and Heroina – to ensure accuracy, arriving at the 1.5 million penguin figure.

Lynch said the work shows how technology can be deployed to further conservation science.

“We’re certainly not the first to use UAVs for counting penguins, but this was a nice demonstration of the technology and we were fortunate to have good weather during the expedition to fly the UAV,” she said. “The biggest takeaway [from the study] is that this validates the use of satellite imagery as an important management tool, and we need to make sure that the marine protected areas being designed in this region account for this massive penguin hotspot,” said Lynch.

Currently, the international body that governs Antarctic marine conservation is considering a proposal to create a marine protected area in the Weddell Sea. However, as presently drawn, its boundaries would not encompass the Danger Islands. Lynch and her colleagues hope that their discovery would lead to an expansion of the proposed marine protected area’s borders, providing the penguins an additional buffer from human activities and climate change.

The discovery of this enormous and previously unknown Adelie penguin population, which the study said contained more individuals than the rest of the region combined, offers hope for the species. Adelie populations have steeply declined in recent decades on the western side of the Antarctic Peninsula, and in 2016 scientists projected a 30 percent decline by 2060 in Adelie penguin colonies across Antarctica, based on current population losses.

But on the Danger Islands on the eastern side of the peninsula, the penguins seem to be doing well. By using limited older aerial images taken in 1957 and satellite images from 1990, the scientists surmised that the population has remained stable or may have even increased somewhat over the last 60 years. Why Adelie penguins are doing relatively well in some areas but are struggling to survive in others isn’t fully known, but scientists believe it has to do with ecosystem shifts caused by climate change.

Western Antarctica – which includes the full Antarctic Peninsula – “is an area of very significant climate change over the past decade,” noted Michael Polito, assistant professor of oceanography and coastal sciences at Louisiana State University and a coauthor of the study. He said there have been “large fluctuations in temperature, sea ice and fluctuations in organisms penguins eat, including krill” in the region.

Megan Cimino, a postdoctoral scholar at Scripps Institution of Oceanography who was not involved in the study, said that the discovery made by Lynch’s team is significant particularly because “Adelies are considered to be a top predator, playing an important role in the Antarctic food web.” Scientists consider penguins a key Antarctic indicator species and the health of their populations, which are easier to study than, say, tiny fish or whales, can serve as a proxy for the broader health of the ecosystem.

Krill, the food that species like penguins and whales eat, are highly sensitive to changes in ocean temperature. In January, scientists published a study projecting a 25 percent decline in krill in an area near the Antarctic Peninsula if greenhouse gas emissions continue to increase. The study’s authors noted that krill decline caused by warming could have even more dramatic effects if Antarctic krill fishing continues at present catch levels. According to scientists, a large, sustained loss of krill could significantly reduce the survival of Antarctic predators, especially penguins. So can variability in sea ice.

“During the summer, too much sea ice could prevent Adelie penguins from getting to or leaving their colony,” said Cimino. “Not enough sea ice in winter may force the penguins to travel further distances to find suitable habitat at the sea ice edge.”

So while the discovery of the Danger Islands penguins offers hope for future conservation, especially because scientists predict the area’s climate will stay relatively stable, there are no guarantees.

“The good news in this story is that this region is projected to be more stable under climate change than other areas further west,” said Lynch. “So we have a large population in what we think will be, at least for the foreseeable future, a climate change refugia.”