Largest On Earth: Caribou Migration

The caribou migration is the longest land migration on planet Earth. Joining the arctic tern and humpback whale who hold the respective records in air and sea, the caribou (Rangifer tarandus) walk 2,000 miles each year between their winter and summer grounds. Though they are also called reindeer, caribou don’t carry a flying sleigh around the globe at Christmas. However, the migration of these magnificent mammals inspires reverence and awe. Learn more about caribou ecology and the great caribou migration here!

Caribou Ecology

Caribou (Rangifer tarandus) are large mammals that evolved for life in the arctic. With adaptations like long legs for walking through deep snow, broad hooves for a snowshoe effect, and thick wooly fur for warmth, they live in one of the harshest climates on planet earth. Their coats change color throughout the seasons from shades of brown to white and gray, but they nearly always have a white neck and rump. 

Antlers All Around! Male vs. Female

Male and female caribou are called bulls and cows. Bull caribou are much larger, in both height and girth, weighing up to 400 pounds. Cows on the other hand are more slender, topping out around 225 pounds. From a distance, it might be a challenge to tell the difference between the two because both male and female caribou have antlers! Caribou are the only member of the deer family with this phenomenon. While across the genera, males use their antlers to compete for mates, you might wonder why females also develop antlers. It’s also about competition for them. During the late spring and summer after calving, the caribou form giant herds, putting pressure on food resources. Female caribou use their antlers to defend their food for themselves and their newborns.

Habitat 

Caribou live on the arctic tundra, boreal forests, and mountains of Eurasia and North America. In fact, caribou live nearly anywhere above 50° north in latitude around the globe with the caribou migration spanning across the arctic. The boreal forests, also called the taiga, are swampy forests of coniferous trees. Further north, the arctic tundra stretches to the ice cap. Though treeless, stunted shrubs, herbaceous plants, and lichens grow on the icy plain. Both the boreal forest and arctic tundra sport a layer of permafrost in the soil, which creates standing water to create bogs and swamps.  

Diet

If you see a caribou, it will likely be eating. Caribou are herbivorous and take advantage of any moment to graze. They eat predominantly herbaceous (non-woody) parts of plants, like leaves and grasses. Their favorite foods are willow and birch leaves, some sedges and grasses, and even mushrooms! In the winter months, lichen becomes the lifesaver. In the winter months, their powerful noses help them sniff out food beneath the snow. Scraping away the snow with their hooves, the caribou can dig down to the rock, revealing a feast of tiny lichens.

Though hard to digest and not very tasty, even humans have eaten lichen when there are no other options. Inuit people use reindeer moss as herbal medicine to treat sickness. Around the world, lichens are also used to flavor teas and bitters. If you find yourself stuck in the arctic without food, the caribou can show you the way to the lichen!

Life Cycle

While grizzly bears, wolves, and other carnivores hunt baby caribou, adults are rarely taken down by a predator. With the advantage of size, antlers, and a herd of their closest friends, they stay protected. However, while they may defend each other against a bear, caribou are not safe from each other. During the rut in the late fall, bull caribou compete for mates. Fighting with their antlers, males often are injured and worn down. Because of this, males only live an average of 4.5 years in the wild, while females can live up to 15 years. 

Reproduction

The rut begins in late fall when the pressure on the males sets in. The bull caribou stop feeding during this time, dedicating all of their energy and fat reserves to the rut. Naturally, fighting and competing leave them exhausted and sometimes fatally injured. The males that are successful restrict access to a group of about ten females. 

Females reach sexual maturity around two years. If they are in good health, a female can bear one calf each year. However, stressed conditions often force females to skip a year here and there. The calves are born in late spring often within a few days of each other, nurse until the early fall, and stay with their mothers until the following calving season.

Four Caribou Subspecies

While all the Caribou in the world fall under the same species, the caribou in Alaska differ from those in Greenland. In fact, there are nine subspecies of caribou including worldwide. North America alone is home to four subspecies: the Woodland, Grant’s, Barren-ground, and Peary caribou. Not all the subspecies include herds that have a caribou migration.

Woodland Caribou

The boreal woodland caribou (Rangifer tarandus caribou) are the largest caribou subspecies. Dependent on extensive boreal forests, they are also endangered subspecies. Three-quarters of woodland in Canada is boreal forest, and while the woodland caribou cover the range of the forest, they are generally non-migratory. However, some herds of woodland caribou do move elevation with the seasons. Additionally, there are a couple of woodland caribou herds that are migratory, though these are the exceptions. 

Newfoundland Caribou

The woodland subspecies include Newfoundland’s herd of sedentary caribou. Originally separated into their own subspecies (Rangifer tarandus terraenovae), they are now clumped in with R.t. caribou. The least migratory of all the caribou, the Newfoundland herb includes around 100,000 animals restricted to the island. Interestingly, reindeer in Newfoundland have smaller antlers than their cousins in other parts of the world. Living in mostly forested habitat, smaller antlers allow them to move with more agility through the trees.

Are they migratory caribou? Most herds are not, with a few exceptions.

Peary Caribou

Far north in the arctic Canadian archipelago, the Peary Caribou (Rangifer tarandus pearyi) reign. The smallest of all the subspecies, the Peary Caribou live in an extremely harsh climate. With broader hooves and a thicker coat, these reindeer are meant for the arctic. However, with climate change and a warming habitat, the Peary’s Caribou is perhaps the most at risk, and they are listed as endangered under the Canadian Species at Risk Act. 

Are they migratory caribou? Not up for long-distance journeys, Peary’s caribou make short seasonal migrations between the islands.

Barren-Ground Caribou

The barren-ground caribou (Rangifer tarandus groenlandicus) are the most abundant subspecies. In contrast to the woodland caribou, the barren-ground herds are migratory. They dominate the Northwest Territories of central Canada, ranging from the Tuk Peninsula south to the United States border.

The barren-ground caribou includes the Western Arctic caribou herd, which is the largest caribou herd in the world with over 300,000 individuals.

Are they migratory caribou? Yes – the barren-ground subspecies have a caribou migration!

Grant’s Caribou

Very similar to the barren-ground caribou are Grant’s caribou (Rangifer tarandus granti). Also known as the Porcupine Caribou herd (PCH), they get their names for their calving grounds along the Porcupine River. Though sometimes included in the barren-ground subspecies, Grant’s caribou have a couple of distinguishing features that have earned them their own group. First, the Porcupine herd is one of the largest caribou herds in North America. With 170,000 individuals, the PCH makes quite an impact during the gregarious summer months. 

Their true claim to fame, however, is their migration. The Porcupine herd holds the record for the largest land animal migration. Not only do they travel further than any other caribou, but they also walk further each year than any other creature on land.

Are they migratory caribou? Yes, including the herd with the longest land migration. 

Caribou Migration

Known collectively to travel incredible distances, caribou may travel upwards of 2,000 miles in a single year. One individual holds the record by walking 2,700 miles in a single year! That would be like walking the Appalachian trail every single year! Lifetime achievement for a person is just another day in the life of a caribou. Here, we dive into some of the details about the magnificent caribou migration.

Fun Fact: Not only do they have the travel bug, caribou are also very fast. They can run at speeds up to 50 mph. 

What Drives the Caribou Migration?

First, caribou migrate based on food availability and energy needs. Because of calving, lactation, antler development, and molt, the spring and summer require the greatest dietary needs. As a result, the caribou move in the direction of abundant food. 

Another reason caribou migrate is to avoid predators. Just after birth, baby caribou are extremely vulnerable. The grizzly bears, wolves, and even golden eagles hunt young caribou. By migrating far north and aggregating into massive groups, the caribou get out of the range of some of the more vicious predators that share their wintering grounds.

Are All Caribou Migratory?

Nope! Caribou subspecies and their herds can be divided into migratory or sedentary ecotypes. Migratory ecotypes move seasonally to and from their birthing grounds along predictable routes. Each spring, they return to the same place where the baby caribou are born. Called the natal grounds, these specific landscapes define the herd. For example, the Porcupine Caribou herd’s natal grounds are along the Porcupine River. 

On the other hand, sedentary caribou generally stay in the same area year-round. However, some sedentary herds take an elevational migration, moving to lower altitudes in the winter. 

Caribou Migration Routes of the Porcupine Herd

The record holder for the longest land migration, the Porcupine herd has the most impressive route. The Porcupine herd migration takes them from the arctic coastal plains of Alaska and the Yukon in the summer to the valleys of Western Alaska and central Yukon in the winter. 

Spring Caribou Migration

In the spring, the caribou return to their natal grounds along the coast, but not always to the exact same location. Stretching along the Alaskan and Canadian coasts, each year the exact location of the calving grounds slightly shifts. 

By nature, herd animals are gregarious, meaning they are social and like being in large groups. While rarely seen solitary at any time of the year, caribou form the largest herds during the summer. After calving, the caribou come together in the largest aggregations all year. Likely due to the swarms of mosquitos and flies in early July, grouping together gives the caribou some relief from incessant biting. Once the insects settle down, the groups of caribou section off into smaller herds before the rut.

Fall Caribou Migration

In the fall, the caribou head southwest toward the mountains. Tracking by GPS collars has allowed biologists to see the subtle variations in the wintering grounds. Generally, the Porcupine caribou winter between the Brooks Range and the Old Crow flats in Canada.

Importance for Humans

Caribou play particular importance for indigenous people of North America. The Gwich’in tribe specifically relies on the Porcupine caribou. Sharing the land in eastern and central Alaska, the Gwich’in call themselves the caribou people. The Gwich’in culture is interwoven with the caribou. Not only do caribou play a role in their spirituality, but they also hunt the caribou for food, clothes, and materials. 

Conservation and the Caribou Migration

Unfortunately for both the caribou and the cultures that rely on them, caribou populations are at risk. The Porcupine herd specifically is targeted by oil drilling in Alaska, but caribou around the globe are threatened by the impacts of climate change.

The Fight for ANWR

In 1960, President Eisenhower established the Arctic National Wildlife Refuge (ANWR) to preserve the integrity and beauty of Alaska’s wilderness. The nesting and denning area to polar bears, grizzly bears, and waterfowl, ANWR provides critical habitat for many animals. Additionally, ANWR encompasses the entire range of the Porcupine caribou herd. 

The same land along the coastal plains that provides refuge for the Porcupine herd’s calving season likely has oil reserves. Oil developers want to extract the resource, destroying over 300,000 acres of the caribou’s calving habitat. Additionally, the pipelines needed to transport the oil would further disrupt the idyllic ecosystems across ANWR. If drilling is approved in ANWR, it would be devastating for both the porcupine herd and the Gwich’in people who rely on them. 

Pipelines in Alaska disrupt caribou migrations. Image by Troutnut on Shutterstock. https://www.shutterstock.com/image-photo/highway-winds-along-alaska-pipeline-on-392296861 

Caribou and Climate Change

Even with protected habitats, caribou around the globe are at risk of climate change. Initially, warmer temperatures may seem like a perk, meaning a long summer with more forage. However, a warmer fall also means rain instead of snow. While caribou can dig through snow to reach their tasty lichen, the rain will freeze into an icy layer at night. Caribou hooves can’t be used as ice picks, and the reindeer would struggle to find enough food over the winter.  

Magnificent Mammalian Migration

Whether surviving an arctic winter on tiny lichens or journeying the farthest distance on land, caribou are tough, resilient, and impressive. However, preserving their habitat and slowing the effects of climate change is critical to the survival of caribou. Between grassroots activism and political change, saving the caribou and their arctic habitat is possible, but quick action is critical. Let’s work to keep these amazing mammals around for future generations!

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[Featured Image by Sherri Cassel on Shutterstock]