What Caused the Halley Bay Colony of Emperor Penguins in Antarctica to Disappear Overnight?

A catastrophic sea-ice collapse off the Brunt Ice Shelf in Antarctica, in 2016, saw thousands of emperor penguin chicks disappear overnight

What Caused the Halley Bay Colony of Emperor Penguins in Antarctica to Disappear Overnight?

Emperor penguin colonies have thrived in Antarctica since time immemorial, as an abundance of sturdy patches of sea-ice serves as ideal breeding grounds for this tallest and heaviest of all living penguin species.

One such colony was in Halley Bay, on the edge of the Brunt Ice Shelf in the Weddell Sea, where, on an average, some 14,000 to 25,000 breeding pairs flocked every year to breed and raise their fledglings until they were able to fend for themselves.

The colony was the world’s second-largest, representing 5 to 9 percent of the global population of these flightless beauties.

However, thousands of emperor penguin chicks were lost overnight, in 2016, when the sea-ice they were being raised on collapsed under the onslaught of a severe storm.

The hapless hatchlings drowned in the freezing waters of the Weddell Sea, as their feathers were not developed-enough for swimming.

The mass drowning of the little emperors was first spotted and reported by British Antarctic Survey (BAS) scientists, Dr. Peter Fretwell and Dr. Phil Trathan, who noticed the missing Halley Bay colony while studying satellite images.

The species took a massive hit that fateful day, but what’s even more disturbing is that adult emperors have not returned to the breeding site ever since – probably due to the fact that a huge iceberg is predicted to disrupt the site, anyways.

Another reason that has kept the birds away from the spot is the fact that the sea-ice that broke off from the side of the sturdier Brunt shelf never really formed properly to support breeding.

Dr. Fretwell – who is the lead author of the paper entitled, “Emperors on thin ice: three years of breeding failure at Halley Bay,” published in the journal Antarctic Science, said:

“We have been tracking the population of this, and other colonies in the region, for the last decade using very high resolution satellite imagery.
“These images have clearly shown the catastrophic breeding failure at this site over the last three years.

“Our specialized satellite image analysis can detect individuals and penguin huddles, so we can estimate the population based on the known density of the groups to give reliable estimate of colony size.”

Being the tallest and heaviest of all extant penguin species, emperor populations as large as the doomed Halley Bay colony need strong and firm sea-ice under their feet – strong enough to withstand the forces of nature and last until their babies have developed the right feathers for swimming.

The length of time we’re looking at is about nine months, as the birds arrive in April and stay until their offspring fledge in December; that’s how long the sea-ice needs to stay colony-worthy.

If, for some reason, the sea-ice breaks up too soon, then a repeat of what happened in 2016 is a foregone conclusion.

Here’s how Dr. Fretwell explained the situation:

“The sea-ice that’s formed since 2016 hasn’t been as strong. Storm events that occur in October and November will now blow it out early. So there’s been some sort of regime change. Sea-ice that was previously stable and reliable is now just untenable.”

However, all is not lost, as a majority of the breeding pairs that lost their chicks in 2016, have moved to safer breeding sites across the waters of the Weddell, with one colony near the Dawson-Lambton Glacier witnessing a “ more than tenfold increase in penguin numbers,” say the authors.

They have, however, not been able to explain why the sea-ice did not redevelop on the Brunt Shelf’s edge; they have no reason or evidence to attribute this to climate change or to anomalies in atmospheric and oceanic conditions in the Brunt Shelf region.

“It is impossible to say whether the changes in sea-ice conditions at Halley Bay are specifically related to climate change, but such a complete failure to breed successfully is unprecedented at this site,” said Dr. Trathan.

That said, Dr. Trathan believes that global warming will impact the continent’s, and indeed the world’s, emperor penguin populations, in the long run, as strong sea-ice will become increasingly hard to come by in warmer waters.

If computer models of the effects of global warming are anything to go by, we could well be looking at a 50 to 70 percent depletion in the world’s emperor population by the end of this century.

“Even taking into account levels of ecological uncertainty, published models suggest that emperor penguins numbers are set to fall dramatically, losing 50-70 percent of their numbers before the end of this century as sea-ice conditions change as a result of climate change,” Trathan said.

“They’re an important part of the food web; they’re what we call a mesopredator. They’re both prey for animals like leopard seals but they also prey themselves on fish and krill species. So, they do play an important role in the ecosystem,” Dr. Michelle LaRue, an ecologist at the University of Canterbury in New Zealand, told BBC News.

“What’s interesting for me is not that colonies move or that we can have major breeding failures – we know that. It’s that we are talking here about the deep embayment of the Weddell Sea, which is potentially one of the climate change refugia for those cold-adapted species like emperor penguins,” Dr. Trathan said.

“And so if we see major disturbances in these refugia – where we haven’t previously seen changes in 60 years – that’s an important signal,” he added

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