Adélie penguins have had a hard time on the western side of the Antarctic Peninsula, where warming due to climate change is faster than almost anywhere else in the world. That and other factors have led to a sharp decline in Adélie populations in recent decades.
But on the east side, it’s a different story.
“It’s just a complete train wreck on the west side of the peninsula,” said Heather J. Lynch, a statistical ecologist at Stony Brook University who studies penguin populations and how they change. “But on the eastern side, the populations are stable and fairly healthy.”
dr. Lynch uses satellite imagery in much of her work, but also organizes penguin surveying expeditions to the peninsula, the northernmost part of the Antarctic continent. On the latter, in January, three of her current and former PhD students counted on islands on the eastern side of the peninsula in the Weddell Sea.
Their work showed that Adélie populations there have changed little from previous censuses over the past two decades. That suggests that as global warming continues and Adélie populations in other parts of the continent decline, the Weddell may continue to be an important refuge for the birds.
“It’s a nice confirmation that where the climate hasn’t changed so dramatically, populations haven’t changed dramatically,” said Dr. Lynch.
The Weddell Sea is notoriously icy, a function of a rotating current, or gyre, that keeps much of the pack ice in the sea for years. The ice makes it difficult for most ships to navigate. (The Weddell is where explorer Ernest Shackleton’s ship Endurance was crushed by ice a century ago. The wreckage was found last month.)
Over the years, Dr. Lynch penguin surveys done from ships of opportunity, often sailing cruise ships in exchange for lecturing and otherwise helping. In the Antarctic Peninsula, those ships usually stay on the west side, and regulations limit visits to the coast to a specific set of colonies.
The January trip was aboard a Greenpeace ship that ventured around the tip of the peninsula to the northwest of Weddell. “It’s somewhere we wanted to go,” said Dr Lynch. “Many of these colonies hadn’t been visited for a very long time, if ever.”
The three researchers – Michael Wethington, Clare Flynn and Alex Borowicz – used drones and counted by hand to determine the number of chicks in colonies on Joinville, Vortex, Devil and other islands.
Counting by hand takes time, says Ms. Flynn, a first-year doctoral student at Stony Brook. Counters identify a specific area within a colony — perhaps a group of nests, or an area delineated by the bird’s trails — and count all the chicks in it three times to ensure accuracy. At Penguin Point, a particularly sprawling colony on Seymour Island with 21,500 chicks, the count took two days. (Adélies produces two chicks per breeding pair each year.)
“It’s getting tedious to count them three times,” Ms Flynn said. “But it’s just such a great place to be and such a great job to do.” And the birds can be entertaining, she said, like when a hungry chick furiously chases after a parent demanding food.
Adélies are among 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 collect small stones to build nests on dry land. Chicks hatch around November, late spring in the Southern Hemisphere, and the parents take turns guarding them, searching for food that they regurgitate for their offspring. Antarctic Peninsula Adélies are picky about their diet, eating only krill, a small crustacean, although they also eat fish elsewhere.
Krill and ice, or the lack of both, are at the root of the problems of the Adélies on the western side of the peninsula, which has warmed in part due to atmospheric circulation patterns originating in the warming tropics. Krill thrive in cold, icy conditions, so because warming has reduced sea ice, krill has also become less abundant.
As a result, Adélies does not have enough of the food they need for themselves and their chicks. “The fact that they are such picky eaters on the peninsula is to their disadvantage, as they are very linked to the health of the krill population,” said Dr. Lynch.
Populations have declined by as much as 90 percent in some parts of the western side, and Gentoo penguins, distinguishable by their bright orange beaks, have largely taken over. “They eat everything, they breed everywhere,” said Dr. Lynch on Gentoos. “I see them as the urban scourges of the peninsula.”
As the world continues to warm, models suggest the Weddell and Ross Sea in West Antarctica will be the last places to turn unfavorable for Adélies.
The Weddell has also been proposed as a marine protected area under the Antarctic Treaty, which would further protect the penguins and other life there from human activities such as krill fishing, especially as warming reduces ice cover and makes the area more accessible. “As scientists, we want to map where all the important biology is,” said Dr. Lynch.
The finding that populations are stable “doesn’t mean that climate change isn’t happening in the Weddell Sea,” she said. “It just means that because of the oceanography it stays cold and icy and is exactly the kind of place these Adélies have to live in.”