Caribou Migration: What Is It and Why Do They Do It?

Written by AZ Animals Staff
Published: September 1, 2021
Written by AZ Animals Staff
Published: September 1, 2021


When we think about migration, we typically think of birds flying south for the winter, but actually other animals, in particular some species of caribou Rangifer tarandus, also migrate. Unlike birds, who are primarily avoiding harsh winter weather and temperatures, however, caribou migrate for a variety of reasons.

One reason Caribou migrate is in order to reach remote birthing grounds. This is so that their newborn young are protected from predation from golden eagles, wolves, and grizzly bears during the calves’ most vulnerable early days.

Another reason for their travel is to reach northern ice fields, thereby staying away from mosquitos that would otherwise plague them in warmer months. And finally, they return south when the weather grows colder.

Migration also allows them to avoid overgrazing specific areas and gives the animals the ability to eat whatever food is growing most abundantly in each season. For instance, in winter, their diet will consist primarily of abundant lichen more commonly known as reindeer moss.

What Are Caribou?

Caribou Migration
The Cairngorm reindeer in a beautiful colorful landscape in the autumn of Scotland.

If the term caribou is unfamiliar to you, perhaps their other name is more familiar. These relatives of the deer are also known as reindeer, which almost certainly explains why the lichen they feast on in winter is referred to as reindeer moss. In North America, they are typically referred to as reindeer only when domesticated, whereas the free-roaming wild herds are called caribou. Their scientific name is comprised of two different words for “reindeer,” one Latin and the other New Latin.

Some interesting facts about caribou, including that they, among all the animals in the world, are the only ones known to be able to see ultraviolet light and they are the only member of the deer family where both the males and the females will grow antlers.

These animals also live about 15 years, weigh up to 700 lbs, and, even when one day old, can reach speeds faster than human sprinters. It is an unfortunate truth that, despite their high population numbers, their survival is potentially being threatened by arctic drilling. While some species appear to be thriving others are considered endangered and at risk of going extinct.

Caribou Herd Facts

The largest caribou herd is probably the Western Arctic Herd, which at its peak consisted of nearly 500,000 animals and still has numbers close to 260,000. Its migration territory covers over 150,000 miles of Alaska, an area larger than the whole state of California.

Perhaps the best known of the migrating caribou herds is that of the Porcupine Caribou in Alaska, located primarily within the Arctic National Wildlife Refuge and named for the river they migrate along. There are nearly 200,000 of them, and on their route, they traverse an area that is equivalent on the map to the size of the state of Wyoming, across the Alaska refuge, and also into parts of the Northwest Territories and the Yukon in Canada.

By contrast, the Central Arctic Caribou Herd had only about 22,000 at their last count in 2016, down from 70,000 only six years prior. Not all of the Central Arctic herd actually migrate and those that do have a much larger roaming area.

Scientists use a radio tracker collar on select members of the herd, as well as low altitude photography, in order to follow their migration patterns each year. These trackers have taught biologists a lot about the traveling habits of these intriguing creatures. In July of 2003, it took a team of 13 biologists with four planes and a large mapping camera in order to count the herd population of the Western Arctic Herd. They took more than 1000 photos in order to accurately assess the numbers.

Scientists take a herd census every three years, weather and conditions permitting. This lets them know whether herd populations are rising or falling, and also whether migration patterns have changed significantly from the prior census.

Caribou Migration
Caribou herd on pastures in the mountains of Kamchatka in Russia.

When Do Caribou Migrate and How Far?

The typical caribou migration route for the various North American species begins in spring, during the month of April. This is when pregnant cows and the rest of the herd begin their 400-mile trek toward the herd’s specific birthing fields, which are located on the arctic coastal plain for the Porcupine herd. Oftentimes only maternal cows will make the full journey into the calving grounds, with males and non-maternal females staying on the outskirts of the grounds until migration begins again.

The next leg of their migrating journey begins in summer, during late June or early July when the biting pests known as mosquitoes begin to hatch out in huge numbers. In order to avoid being endlessly bitten, the caribou head further north during this time, up toward the ice fields near the Brooks Range, which are too cold for mosquitoes to survive. They will only stay there a few weeks before they start heading back south, toward wherever they plan to spend the fall and winter.

This varies from year to year and is sometimes in the refuge in Alaska for the Porcupine herd, and sometimes in Canada. In total, their trek across the map takes them as many as 3000 miles.

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