Mystery of mass caribou deaths solved | Polarjournal
After the remains of countless caribou were found on two islands in the North American Arctic in 1966 and 2016, scientists have now found the cause of the mass die-off. Photo: Ben Townsend via Flickr, CC BY 2.0

For decades, researchers puzzled over the cause of mysterious mass deaths of caribou in the North American Arctic. In 1966, biologists found skeletons of thousands of animals on St. Matthews Island in the Bering Sea, and in the summer of 2016, a survey team again discovered countless dead caribou, this time on Prince Charles Island in Nunavut, Canada, 6,800 kilometers to the east. Using satellite data, NASA scientists have now been able to decipher the cause of the mass death of the animals.

There were dozens of carcasses scattered across the tundra of Prince Charles Island in the summer of 2016. According to estimates, the animals had been dead for at least several weeks, possibly since late winter. Some animals died lying down, others apparently just collapsed.

Exactly 50 years earlier, biologists on St. Matthews Island were confronted with an even more grisly picture: 42 animals from a herd that had numbered 6,000 caribou three years earlier were searching for food among the skeletal remains of thousands of members of their herd.

In 1966, the remains of a 6,000-animal caribou herd were found on St. Matthews Island in the Bering Sea. Only 42 animals had survived. Photo: Landsat/Joshua Stevens, NASA

Caribou and reindeer belong to the same species (Rangifer tarandus) but do not share the same way of life. North American caribou migrate in massive herds over large distances between their breeding and wintering grounds, while reindeer in Europe and Asia rarely migrate and some live in domesticated herds.

Whether caribou or reindeer, both feed on plants and lichen, which they find under the snow even in winter. In late autumn and early spring, when the snow cover is often covered by a hard crust of ice, they use their sharp hooves to reach the food. Although the animals manage their energy reserves well over the winter, they ran out of time on both islands.

Conditions on Prince Charles Island in Nunavut, Canada, can be harsh and unforgiving even in summer, as the caribou painfully experienced in 2016. Photo: Landsat/Joshua Stevens, NASA

To find out what caused the mass die-offs in the two herds, scientists evaluated extensive weather data, from satellites and from ground sensors. The results provided them with the answer. Prince Charles Island experienced severe storms with heavy snowfall in April 2016, at a time when caribou energy reserves are at their lowest after the long winter. The storms brought an unusually dense snow cover and made it impossible for the caribou to reach their food, resulting in starvation.

The same fate befell the great herd half a century earlier on St. Matthews Island. The scientists found from the data that the winter of 1963-64 was one of the harshest ever recorded in the Bering Sea Islands. At the time, the Caribou were battling hurricane-force storms, wind chills of minus 57.5 degrees Celsius and a record amount of snow. Here, too, the hard-frozen snow cover posed too great an obstacle for the animals. They found little or no access to their food when they needed it most and starved as well. Two years later, only 42 of the once 6,000 animal herd were still alive.

Julia Hager, PolarJournal

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