A massive colony of Adelie penguins has been discovered in Antarctica, surprising scientists who had thought their numbers were in decline.

The 1.5 million penguins were spotted on the Danger Islands, a chain of nine rocky islands off the Antarctic Peninsula's tip, near South America.

The first bird census there found around 750,000 breeding pairs.

A team led by researchers from the US-based Woods Hole Oceanographic Institution reported their discovery in the journal Scientific Reports.

Image: The penguins can grow up to 70cm tall. Pic: Rachael Herman, Louisiana State University, Stony Brook University

Study co-author Heather Lynch said it had "real consequences for how we manage this region" and that "the Danger Islands weren't known to be an important penguin habitat".


This may have been because of their remoteness and the difficult waters that surround them: even in the summer, anyone trying to reach the islands can expect to deal with thick sea ice.

Four years ago, Ms Lynch teamed up with Mathew Schwaller from NASA and examined satellite images that hinted at a curiously large number of penguins in the area.

Image: Adelie penguins are one of five species in the area. Pic: Woods Hole Oceanographic Institution

Determined to verify the find, she set out on an expedition with a team of researchers.

They arrived in December 2015 and counted the birds with the help of a drone that took pictures once every second.

The photos were then stitched together to give a comprehensive picture.

Image: A drone was used to help count the penguins. Pic: Stony Brook University

One of those on the expedition, Michael Polito, from Louisiana State University, said the islands "appear to have not suffered the population declines found along the western side of Antarctic Peninsula that are associated with recent climate change".

Just 100 miles away, on the peninsula's west, Adelie numbers have dropped by around 70% in recent decades due to melting sea ice, something blamed on global warming.

Image: Adelie penguins can be recognised by the white ring around their eyes

Ms Lynch said: "One of the ways in which this is good news is that other studies have shown this area (the eastern side of the Antarctic Peninsula) is likely to remain more stable under climate change than the western Antarctic Peninsula.

"So we end up with a large population of Adelie penguins in a region likely to remain suitable to them for some time."

Adelie are one of five species that live in and around Antarctica.

They grow to a height of about 70cm and weigh between three and six kilograms.