March 2 (UPI) -- Scientists have found another 1.5 million penguins living in Antarctica.
Ecologists had grown concerned in recent years as they counted fewer and fewer Adélie penguins, once the most abundant species in Antarctica. It turns out, population surveys were ignoring a super-colony just off the coast of the Antarctic Peninsula's northern tip.
With the help of satellite images, scientists were able to locate 1.5 million Adélie penguins congregating on a remote, jagged outcropping of islands known as the Danger Islands.
"Until recently, the Danger Islands weren't known to be an important penguin habitat," Heather Lynch, an associate professor of ecology and evolution at Stony Brook University, said in a news release.
Satellite images of the island chain didn't reveal penguins themselves, but researchers were able to pick out the telltale signs of a large colony -- large guano stains.
Inspired by their discovery of seabird excrement, researchers set off in search of the birds themselves. In 2015, a research ship delivered a team of scientists to the islands. The team used a drone to help them survey the islands.
"The drone lets you fly in a grid over the island, taking pictures once per second. You can then stitch them together into a huge collage that shows the entire landmass in 2D and 3D," said Hanumant Singh, professor of mechanical and industrial engineering at Northeastern University.
Singh helped scientists develop the imaging software. He also designed algorithms to scan the collected images and identify the location of penguin nesting sites.
Ice loss and rising temperatures are a threat to penguins in both the Arctic and Antarctica, but the latest discovery suggests some colonies and their habitats remain resilient.
"Not only do the Danger Islands hold the largest population of Adélie penguins on the Antarctic Peninsula, they also appear to have not suffered the population declines found along the western side of Antarctic Peninsula that are associated with recent climate change," said Michael Polito, a researcher at Louisiana State University.
Additional surveys of the Danger Islands and the penguins that live there could help scientists better understand what makes the habitat there more desirable.
"The population of Adélies on the east side of the Antarctic Peninsula is different from what we see on the west side, for example," said Stephanie Jenouvrier, a seabird ecologist at Woods Hole Oceanographic Institute. "We want to understand why. Is it linked to the extended sea ice condition over there? Food availability? That's something we don't know."
Scientists detailed their discovery of the new super-colony in a new paper published this week in the journal Scientific Reports.