Life hasn’t been easy for Adelie penguins who live on the western side of the Antarctic Peninsula, where warming linked to climate change is occurring at a faster rate than virtually anywhere else on the planet. This and other factors have led to the sharp drop in penguin populations in recent decades.
But on the eastern side, the story is different.
“On the west side of the peninsula, the situation is disastrous,” said Heather Lynch, a statistical ecologist at Stony Brooks University who studies penguin populations and their recent transformations. “On the east side, populations are stable and healthy.”
Lynch uses satellite imagery in much of his work, but he also organizes expeditions to the Antarctic Peninsula, the northernmost part of the Antarctic continent, to survey penguin populations. On the last of these expeditions, in January, three of her former and current doctoral students performed the count on islands on the east side of the peninsula, in the Weddell Sea.
Their work revealed that the area’s Adélie penguin populations have changed little from previous counts carried out over the past two decades. This suggests that as global warming continues and Adelie penguin populations dwindle elsewhere in Antarctica, the Weddell Sea could continue to function as a refuge for birds.
“It’s confirmation that in places where the climate hasn’t changed that much, the populations haven’t changed that much either,” Lynch said.
The Weddell Sea is notoriously icy, thanks to a rotating current, or gyre, that keeps much of the ice compacted within the sea for years. Ice makes navigation difficult for most ships. (It was in the Weddell Sea that explorer Ernest Shackleton’s ship Endurance was crushed by ice a century ago. The wreckage of the Endurance was located last month.)
Over the years Lynch’s students have surveyed penguins from cruise ships in exchange for giving lectures and helping in other ways. On the Antarctic Peninsula, these ships are usually on the western side. There are regulations that limit visits to the coast to a specific set of colonies.
The January voyage was made on a Greenpeace ship that circled the tip of the peninsula, arriving northwest of the Weddell Sea. “It’s a place we’ve been wanting to go,” Lynch commented.
The three researchers — Michael Wethington, Clare Flynn and Alex Borowicz — used drones and manual counts to determine the number of chicks present in Adelie penguin colonies on the islands of Joinville, Vortex, Devil and others.
Flynn, who is a doctoral student at Stony Brook University, said manually counting birds takes time. The counters identify a specific area of ​​the colony — this could be a cluster of nests or an area delineated by the paths formed by the penguins’ gait — and count all the chicks within the area. To ensure accuracy, counting is performed three times. At Penguin Point, a large colony on Seymour Island that is home to 21,500 pups, the count took two days.
Each breeding pair usually produces two young a year.
“It’s exhausting to count the pups three times,” Flynn said. “But it’s an amazing place and an amazing job to do.”
Adelie penguins are one of the most numerous penguin species found in Antarctica, with an estimated 3.8 million breeding pairs in colonies across the continent. They use their beaks to gather stones to build nests on dry land. The chicks are hatched around November, in the late spring of the southern hemisphere, and the parents go out in search of food that they regurgitate to give to their offspring. Adelie penguins on the Antarctic Peninsula are selective about their diet — they eat only krill, a small crustacean — although those elsewhere also consume fish.
Krill and ice, or a lack of both, are at the root of the Adelie penguin’s problems on the western side of the peninsula, where temperatures have been rising in part as a result of atmospheric circulation patterns that have their origins in the tropics. in the process of heating. Krill does well in icy conditions, but just as warming is causing sea ice to decline, krill is also less abundant.
This leaves Adelie penguins without a sufficient supply of food. “The fact that penguins on the peninsula are so selective about what they eat hurts them, because it makes them very tied to the health of the krill population,” Lynch said.
Adelie penguin populations have declined by up to 90% in parts of the western side, and their place is being taken by gentoo penguins, with their bright orange beaks. “Gentoo penguins will eat anything and breed anywhere,” Lynch commented. “I think of them as the urban plagues of the peninsula.”
Models suggest that with global warming continuing, the Weddell Sea and Ross Sea in West Antarctica will be the last places to become unfavorable for Adelie penguins to survive.
It has been proposed that the Weddell Sea become a marine protected area under the terms of the Antarctic Treaty, which would protect the penguins and other life there from human activities such as krill fishing, especially as water cover ice shrink due to heating, making the area more accessible. “As scientists, we want to map out where all the important biology is” for this effort, Lynch said.
The finding that populations are stable “doesn’t mean climate change isn’t happening in the Weddell Sea,” she said. “Due to oceanographic conditions, this region remains icy and remains exactly the kind of place these Adelie penguins need to live.”
Translation by Clara Allain
