Adélie penguins have had a rough time on the western
side of the Antarctic Peninsula, where warming linked to
climate change has
occurred faster than almost anywhere else on the planet. That and other factors
have led to sharp declines in Adélie populations in recent decades.
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But on the east side, it’s a different story.
“It’s just a complete train wreck on the
western side of the peninsula,” said Heather Lynch, a statistical ecologist at
Stony Brook University who studies penguin populations and how they are
changing. “But on the eastern side, the populations are stable and quite
healthy.”
Lynch uses satellite imagery in much of her
work, but she also organizes penguin-surveying expeditions to the peninsula,
the northernmost part of the Antarctic continent. On the latest one, in
January, three of her current and former doctoral students did the counting at
islands on the eastern side of the peninsula in the Weddell Sea.
Their work showed that Adélie populations
there have changed little since previous counts taken over the past two
decades. That suggests that as global warming continues and Adélie populations
decline in other parts of the continent, the Weddell may remain a refuge for
the birds.
“It’s a nice confirmation that where the
climate has not changed as dramatically, the populations have not changed
dramatically,” Lynch said.
The Weddell Sea is notoriously icy, a
function of a rotating current, or gyre, that keeps much of the pack ice within
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 wreck was found last month.)
Over the years, Lynch’s students have done
penguin surveys from cruise ships in return for giving lectures and otherwise
helping out. On the Antarctic Peninsula, those ships usually stay on the
western side, and regulations limit shore visits to a specific set of colonies.
The January trip was on a Greenpeace vessel
that sailed around the tip of the peninsula into the northwestern Weddell.
“It’s somewhere that we’ve wanted to get to,” Lynch said.
The three researchers — Michael Wethington,
Clare Flynn, and Alex Borowicz — used drones and hand-counting to determine the
number of chicks at colonies on Joinville, Vortex, Devil, and other islands.
Hand-counting takes time, said Flynn, a
doctoral student at
Stony Brook. Counters identify a specific area within a
colony — perhaps a grouping of nests, or an area delineated by the birds’
walking paths — and count all the chicks within it three times to ensure
accuracy. At Penguin Point, a sprawling colony on Seymour Island that is home
to 21,500 chicks, the counting took two days. (Adélies normally produce two
chicks per breeding pair each year.)
“It does get tedious, counting them three
times over,” Flynn said. “But it’s just such an amazing place to be and such an
amazing job to be doing.”
Adélies are among the most numerous of the
penguin species found in Antarctica, with an estimated 3.8 million breeding
pairs at colonies all around the continent. They use their beaks to gather
stones to make nests on dry land. Chicks hatch around November, late in the
Southern Hemisphere spring, and the parents forage for food that they
regurgitate for their offspring. Antarctic Peninsula Adélies are choosy about
their diet: They eat only krill, a small crustacean, although elsewhere, they
also eat fish.
Krill and ice, or the lack of both, are at
the root of the Adélies’ problems on the western side of the peninsula, which
has been warming in part as a result of atmospheric circulation patterns
originating in the warming tropics. Krill flourish in cold, icy conditions, so
as warming has caused sea ice to decline, krill have become less abundant as
well.
That leaves Adélies without enough of the
food they need. “The fact that they’re such picky eaters on the peninsula is to
their detriment, because they’re very much tied to the health of the krill
population,” Lynch said.
Populations have declined by as much as 90%
in parts of the western side, and Gentoo penguins, with their bright orange
beaks, have largely taken over. “They’ll eat anything, they’ll breed anywhere,”
Lynch said of Gentoos. “I think of them like the urban pests of the peninsula.”
As the world continues to warm, models
suggest that the Weddell Sea and the
Ross Sea in West Antarctica will be the
last places to become unfavorable to 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 ice cover declines from warming and the area becomes more
accessible. “As scientists, we want to map out where all the important biology
is” for that effort, Lynch said.
The finding that populations are stable “doesn’t mean
that climate change isn’t happening in the Weddell Sea,” she said. “By virtue
of the oceanography, it remains cold and icy and exactly the kind of place
where these Adélies need to live.”
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