How Far Do Caribou Migrate? Among the Longest Land Migrations

The longest migrations on land

For a long time, claims about the “longest land migration” relied on rough estimates. In 2019, researchers led by Kyle Joly compared GPS tracking data from large mammals on several continents, from caribou to Mongolian gazelles, wild asses and wolves. They found that caribou herds in Alaska and northern Canada made the longest migrations, with round-trip distances of more than 1,000 km (620 mi) measured in straight lines between seasonal ranges.

The same study found that gray wolves moved the most over a whole year, because predators roam widely in search of prey, but wolves do not migrate in the same regular way. Among migrating land animals, caribou came out on top. The longest animal migrations list shows how this compares with birds, whales and insects.

Real routes are much longer than straight lines. Caribou follow valleys, cross mountain passes and detour around lakes and rivers. When every move is added up, total yearly travel for some animals runs into several thousand kilometers; figures of up to about 5,000 km (3,100 mi) a year are often quoted, though totals like this depend on how often a collar records the animal’s position.

The yearly journey

A typical migratory caribou herd follows the same basic calendar each year:

Migrating caribou usually travel about 19–55 km (12–34 mi) a day. They walk long distances on broad hooves that spread on snow and soft tundra, and they are strong swimmers that cross wide rivers and lakes without hesitation. Calves can follow their mothers within hours of birth and must keep up within days.

The Porcupine caribou herd

The best-known migration is that of the Porcupine caribou herd, named after the Porcupine River that flows through its range in Alaska and Yukon. The herd winters in the Ogilvie and Richardson Mountains of Yukon and the southern Brooks Range of Alaska. Each spring, pregnant cows head north to calve on the Arctic coastal plain near the Beaufort Sea, much of it in the Arctic National Wildlife Refuge.

The herd’s range is often described as covering about 2,400 km (1,500 mi) of travel a year, and its calving grounds are some of the most studied wildlife areas in North America. A 2017 photo census counted about 218,000 caribou, a record high for the herd. The Porcupine caribou are central to the life and culture of the Gwich’in people, whose communities were traditionally placed along the herd’s routes.

Why caribou travel so far

Caribou migrate to follow food and to protect their calves:

• Fresh food: spring green-up on the tundra provides protein-rich new plants just when cows need them most for milk.
• Safety for calves: open calving grounds have fewer wolves and bears than the forest, and many cows giving birth at once overwhelm predators.
• Insect relief: summer winds on the coast and in the mountains help keep away mosquitoes, black flies and warble flies.
• Winter shelter: the forest edge has lichens and softer, shallower snow that is easier to dig through.

Read more about seasonal foods in what do reindeer eat?

Not all caribou migrate

Migration is a lifestyle of certain herds, not the whole species. Barren-ground caribou of the tundra are the long-distance travelers. Woodland caribou of Canada’s boreal forest live in small groups that stay in roughly the same area all year. Island populations such as the Svalbard reindeer and the Peary caribou of the Canadian high Arctic make local movements, sometimes crossing sea ice between islands.

In Eurasia, wild reindeer generally migrate shorter distances, although the huge Taimyr herd of Siberia makes long seasonal journeys. In Scandinavia, Sámi herders move their semi-domesticated herds between inland winter pastures and coastal or mountain summer pastures.

Shrinking herds and blocked routes

Many migratory herds have declined sharply. Canada’s George River herd fell from roughly 800,000 caribou in the early 1990s to fewer than 9,000 by 2018, and Alaska’s Western Arctic herd has fallen from about 490,000 in 2003 to around 150,000 in recent counts. Causes include climate change, which affects snow, ice and the timing of plant growth, along with roads, mines and other development that can block or disturb migration routes. Herd sizes also rise and fall naturally over decades.

Because of these declines, the reindeer, as the species is known in Europe, is listed as Vulnerable by the IUCN. Protecting calving grounds and keeping migration corridors open are key to conserving these journeys.