The Fantastic Fall Migration

It’s fall in Alaska, and that means that a spectacular migration is in full swing. Each year our North American caribou, Rangifer tarandus granti, undertake an epic journey from their breeding range to wintering grounds – one of the biggest large-mammal land migrations on Earth.

The Arctic National Wildlife Refuge is home to two herds of caribou: Latest estimates put the Porcupine Herd at about 169,000 animals, and the smaller Central Arctic herd at 70,000. Can you imagine herds of this size on the move? Yet move they do – in fact, caribou are constantly on the move, looking for more food in the vast Arctic landscape.

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Every summer, caribou herds enjoy the rich, nutritious vegetation of the Arctic tundra and the coastal plain of the Arctic National Wildlife Refuge. While these summer stomping grounds are ideal for raising young, they become harsh and windy places in winter. So when the weather turns and the first snow falls, the caribou begin to migrate south, travelling hundreds of miles to milder weather and more protected habitat in Alaska’s boreal forests.

More than 200,000 caribou on the move is certainly an amazing sight and necessary for these animals’ survival, but the migration has an ecological impact beyond the caribou themselves. Their journey impacts everything, from the vegetation that they eat and trample, to the bacteria that thrive on their droppings, to the predators like wolves and bears that prey on old, sick and young caribou. They’ve made this journey for thousands of years, and the cycle has become an integral part of the changing seasons and systems in the region.

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While their wintering range is friendlier environment than the Arctic tundra this time of year, Alaska’s boreal forests aren’t exactly an easy place to spend the winter, so caribou are specially adapted to cope with harsh conditions. Their winter hair is hollow, which not only insulates them against their chilly surroundings, but also helps them to float high in the water when they need to cross rivers along their migration route. Caribou have four hoofed ‘toes’ on each foot, and though they usually walk on the two largest toes, when travelling through deep snow they can spread out all four to provide more surface area, just like humans using snowshoes. And caribou hooves are sharply shaped, which is great for digging through snow and ice to reach buried food.

Despite all these excellent adaptations, caribou, like many species in the Arctic, may have difficulty keeping up with changes in their habitats. Their home, along with the rest of the Arctic, is warming faster than anywhere else on Earth. A warming climate might sound like a good thing – easier winters, right? – but reality isn’t that simple. For instance, some of the snow that we would usually expect to see in northern Alaska falls as rain instead. But because temperatures are still cold, the rain freezes into a layer of ice on the ground. Caribou are used to battling through snow and ice to reach the lichen they feed on in winter, but with more ice to chip through, they’ll use more energy to do it. Too much effort to reach not enough food can be a serious problem for any species trying to survive the winter.

Another threat comes not from the cold, but from the heat. Alaska has seen more than its fair share of wildfires this year, and experts link the dramatic increase to climate change. A warmer, drier climate is drying out the boreal forests in the caribou’s winter habitat, making it more susceptible to fire. Luckily, the fires that have burned 5 million acres in Alaska this year have largely spared the winter range of the Porcupine and Central Arctic caribou herds. But fire remains an ongoing threat because it can have a marked impact on the lichen that comprises the caribou’s main winter food source. Wildfires can easily destroy the ground-dwelling lichen, and it can take a very long time for these organisms to recover. In the meantime, the herd is faced with a shortage of food at the very time it’s most needed.

Defenders works hard to protect areas like the Arctic National Wildlife Refuge which, in addition to caribou, is home to 36 species of land mammals, eight marine mammals, 42 fish species, and more than 200 migratory bird species. In addition to climate change, potential development by the oil and gas industry could threaten the refuge. We’re committed to preventing development that will harm this fragile ecosystem, and have worked with the Administration and on Capitol Hill to protect the refuge and make sure our decision-makers fully understand how unique and valuable the Arctic Refuge is intact. You can do your part by voting for elected officials that support protecting wildlife refuges, and reaching out to your representatives to make sure they know that protecting the Arctic Refuge and combating climate change are important issues that matter to you.