Why did almost a million king penguins disappear without a trace?

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Why did almost a million king penguins disappear without a trace?
Why did almost a million king penguins disappear without a trace?
Anonim

Almost a million black and white birds have disappeared without leaving any trace. Once the island of Cauchon in Antarctica was densely populated by penguins, but now it is empty. Scientists traveled to the island to test all hypotheses for bird extinction, including disease, predators, and a warming Antarctic Ocean that could be a harbinger of future disasters.

In early 2017, Henri Weimerskirch wondered where all the penguins might have gone. His colleagues sent him aerial photographs of Cauchon Island, a deserted volcanic island located between Madagascar and Antarctica, where people rarely look. These images showed the vast empty cliffs where about 500,000 pairs of king penguins lived just a few decades ago, which nested and raised their offspring there. Obviously, by now this colony - once the largest colony of king penguins and the second largest colony of 18 penguin species - has declined by 90%. Almost 900 thousand black and white birds, reaching a height of 1 meter, disappeared without leaving any trace. “It was just incredible, completely unexpected,” recalls Weimerskirch, who works for the French national research agency CNRS.

Together with his colleagues, he planned to soon go on an expedition to this island - the third expedition to the island in total and the first in 37 years - to try to find an explanation for what was happening. “We had to see it with our own eyes,” said CNRS ecologist Charles Bost.

While the researchers prepared for their expedition, they had to solve the logistical, political and scientific problems that have long plagued biologists trying to study the ecosystems of Antarctica. The vast distances, harsh weather and rugged terrain made expeditions there difficult and costly. Scientists needed a ship - and a helicopter, because icy seas and rocky island shores often made landings in Antarctica extremely risky. Meeting the stringent biosecurity requirements of this French-controlled island - which means scientists are prohibited from disrupting the balance in fragile ecosystems - required meticulous planning and a ton of paperwork that took many months. After arriving on the island, scientists had very little time - only five days - to test all hypotheses for the extinction of penguins, including diseases, predators and the warming of the Antarctic Ocean.

Most likely, these scientists will no longer have a chance to return to Cauchon Island. “We knew this would be the only expedition,” recalls biologist Adrien Chaigne, an expedition organizer working for the French Southern and Antarctic Territories National Park, which controls the island. "We were under tremendous pressure."

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Similar problems have long plagued biologists trying to study the features of life in Antarctica. Two centuries ago, scientists who wanted to get to the region had to sail alongside discoverers, whalers and sealers. For example, the Adélie penguins were first discovered by a naturalist who joined the 1837 expedition to the southeastern part of Antarctica led by the French traveler Jules Dumont d'Urville, who named the place Adelie Land after his wife. Arduous sea voyages ultimately succeeded: in 1895, botanists, convinced that no plant could survive in the icy Antarctic, to their great surprise, discovered lichens on Possession Island, near Cauchon Island.

Today, modern research budgets, as well as an entire network of polar research stations, have made Antarctica more accessible. Biologists have traveled to the region to find answers to a number of fundamental questions, including how animals evolved to survive in subzero temperatures and how ecosystems in the vast Southern Ocean are organized. Climate change, which has made Antarctica the fastest-changing place on planet Earth, has spawned research on phenomena such as glacier movement and ocean acidification. The potential for new discoveries makes the region extremely attractive to scientists, according to marine biologist Deneb Karentz of the University of San Francisco. "If a scientist gets there at least once, he will always want to return."

But even today, Antarctic exploration is fraught with challenges. “If you only need two hours at home to collect the necessary samples, then in Antarctica it will take 10 hours,” explains Karentz. Severe weather conditions can sometimes result in the loss of valuable equipment. In 1987, moving sea ice broke the plexiglass frame that Karenz used to study microorganisms beneath the surface of the water. She had to replace it with a device that she built from materials found at a nearby research station. In Antarctica, she said, "you have to be creative."

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Weimerskirch and Bost, veterans of Antarctic exploration, learned these lessons well when a helicopter from the French research vessel Marion Dufresne flew scientists and 700 kilograms of equipment to Cauchon Island in November 2019. It was the height of the king penguin nesting season, and scientists were greeted with shrieks and chirps from tens of thousands of chicks. But scientists also saw huge empty cliffs that were once infested with penguins. According to scientists, once 67 square kilometers of the island was densely populated by penguins, and now most of this space is empty.

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Family of juvenile Humboldt penguins in the nest of Loro Parque penguinarium in Tenerife

Scientists wanted to find out what led to such a sharp drop in the colony. King penguins, with an estimated 3.2 million birds in Antarctica, are not in immediate danger. In fact, their numbers are now recovering after centuries of hunting them. Meanwhile, about half of the world's penguin species are endangered, and some have recently faced rapid extinction. However, the large losses among relatively healthy penguins point to wider threats, which is why the catastrophic situation on Cauchon Island has caused such alarm among scientists.

Studying king penguins is relatively easy. Unlike their ice-dwelling counterparts such as the emperor penguins, king penguins live on islands in the Subantarctic belt. This means that they can be regularly counted thanks to satellite imagery and that scientists can live in camps near penguin colonies to keep watch over them. During the long breeding season, parents share responsibilities among themselves: one incubates eggs and feeds fluffy brown chicks, while the other goes to the sea to catch fish. According to data from electronic transmitters attached to birds, penguins can travel distances of 500 kilometers in search of food.

The main task of the expedition members was to attach such transmitters to 10 penguins in order to understand if the changes associated with finding and obtaining food could somehow entail such a loss in the population of the penguin colony. It wasn't easy. The group of scientists was allowed to move only along one well-trodden road and work only on the very edge of the colony. Scientists were also allowed to glue these transmitters to bird feathers.

During this time, other members of the group set up traps, cameras and night vision goggles to monitor the behavior of cats and mice, which were once introduced there by whalers and which are known to eat eggs and hunt chicks. In addition, scientists have collected feathers and dug up the bones of penguins, which can serve as clues, including to tell about changes in diet.

“The first two days, the work was very intense,” says Shenyi. “We understood that bad weather conditions could put an end to our expedition at any time.” Fortunately, the team of scientists managed to avoid serious storms, and by the end of the fifth day, they were able to fix the sensors on the penguins and collect all the necessary samples.

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Now a huge amount of data needs to be processed. However, researchers have already put forward several hypotheses regarding the reasons for the sharp decline in the colony of king penguins. For example, land predators obviously did not play any role in this. As a result of examining chicks and adults of penguins, as well as examining bones, scientists did not find any traces of bites from mice or cats, and the cameras installed by scientists did not record a single episode of an attack. (Interestingly, the scientists also noted that the rabbits that were seen there previously disappeared from the island.)

In addition, scientists have not found any sure signs that the penguins have simply gone elsewhere. In a smaller colony on the same island, which could serve as a natural place for resettlement, there were no more than 17 thousand pairs - this is too few to explain the sharp drop in the number of the main colony. According to Bost, they were unable to detect signs - for example, in satellite images - that this colony has moved to some other island.

According to Bost, there is only one rational explanation: "If the penguins are not there, then they are dead." But what killed them?

Obviously not disease. Scientists are awaiting the results of the final analysis of blood samples, but on the island they noticed only a few sick birds and few fresh corpses. “We thought we would find many dead birds there, many birds in poor condition,” says Shenyi. But the birds looked healthy.

Shenyi and his colleagues speculate that changes in the surrounding ocean have caused the penguins to swim much further in search of food. Studies of other king penguin colonies show that birds from Cauchon Island typically swim hundreds of kilometers south in search of food, reaching what is known as the Polar Front or Antarctic Convergence. This polar front is where the cold waters of Antarctica meet warmer waters. Penguins are attracted there by a variety of marine life, especially the abundance of the main prey of birds, glowing anchovies, gathering in huge schools.

This polar front does not stand in one place. Over the years, climatic anomalies such as the El Niño Southern Oscillation or the Indian Ocean Dipole cause the ocean waters in this region to heat up and the polar front shifts southward, that is, closer to the pole and farther from Cauchon Island. When one parent goes on a long journey in search of food, hunger can force the other parent to leave the nest to find food, causing the chicks to die from predators or starvation. Such long journeys make penguins more vulnerable to predators and lead to overwork. These anomalous years bode well for how the Southern Ocean will warm over the next few decades, continually shifting the polar front further and further south.

The evidence that ocean warming could threaten penguins comes from a 2015 study by Bost and his colleagues on a smaller colony of king penguins on Possession Island, 160 kilometers west of Cauchon Island. The island is home to the Alfred Faure research station and has less stringent biosafety regulations that allow scientists to continuously monitor the colony, climatic and oceanographic conditions. In the study, the results of which were published in the journal Nature Communications, scientists analyzed 124 routes of penguins in search of food, which 120 birds traveled over 16 years. The study showed that in those years when the polar front moved south, penguins had to swim hundreds of kilometers further. During the period when these unfavorable conditions were observed, the researchers noted, "the penguin population declined by 34%."

Based on this study, in 2018, the journal Nature Climate Change published a forecast that warming seas and other environmental changes could lead to a decrease in the number of king penguins in half by the end of this century.

Scientists may never be able to figure out if this scenario explains the sharp decline in penguin numbers on Cauchon Island. (Another hypothesis is that this colony has grown to an unusually large size over the decades of especially abundant food, and now it has shrunk to its normal size.) However, the transmitters that scientists attached to 10 birds during the 2019 expedition can give them new tips. Five transmitters continue to transmit data and can do so until 2021.

The data transmitted by these devices have already brought many surprises: they show that some penguins go in search of food not to the south, but to the north. This means that the penguins have begun to hunt on the subantarctic front. “Of course, this is a small sample size,” says Weimerskirch. "But it's very interesting." Transmitter data may also confirm a trend towards longer travel for penguins in search of food, which in turn may indicate that alarming predictions about the impact of climate change are actually quite accurate.

According to scientists, an unexpected sharp decline in the colony of king penguins on Cauchon Island could be a harbinger of future disasters and, possibly, a sharp decline in the number of other penguin colonies. However, after spending five days on the cold island, scientists are now forced to observe birds from afar, realizing that the authorities are unlikely to allow them to send another expedition there anytime soon. Helicopters flying over the island from time to time, as well as satellite imagery, will also help keep track of the fate of the penguins.

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