Christi Heun

Caribou often click to mind during the winter, but what happens during the rest of the year? Let's migrate through eight facts about caribou to learn what defines a caribou herd, why caribou migrate, what the difference is between caribou and reindeer and so much more.

1. Caribou and Reindeer are the Same Species, Rangifer tarandus.  

In North America, caribou are found in Alaska and Canada. Only domesticated caribou (originating from an introduced European stock) are called reindeer. All wild animals are called caribou. In Europe, both domestic and wild animals are referred to as reindeer. All caribou and reindeer worldwide are the same species, but there are seven subspecies.  

Alaska Caribou herds map
Map of Alaska's 31 caribou herds, which are defined by their calving grounds.
2. There are 31 Distinctive Herds of Caribou in Alaska.

Caribou travel in massive groups to the same calving grounds each spring to give birth. A herd is distinguished by the distinct calving grounds it uses. Around September, smaller clusters and individuals begin congregating into larger groups again for fall migration. As a giant herd, caribou travel back from their calving grounds to their wintering grounds where they disperse into small groups or lone individuals until the spring. Herds may crossover and mix on winter ranges.  

Porcupine Herd Bonus Fact
3. Caribou Ankles make a Distinctive, Loud Click.

If you’re near a caribou, you’ll hear something like a loud pen clicking or snapping finger noise. The sesamoid click is made when tendons snap over the sesamoid bones of the caribou ankle. The purpose of the click is uncertain, but the leading theory suggests it helps members of a herd stay in contact, especially during points of low visibility like snowstorms.

4. Not All Caribou Herds Migrate.

Large herds, sometimes numbering up to 500,000 animals, often migrate long distances between summer and winter to find adequate food. And, as outlined in the above bonus fact, the Porcupine Herd undergoes the longest migration of any ungulate. Smaller herds numbering in the hundreds, however, may not migrate at all.

5. Caribou Optimize their Nutrition by Synchronizing Their Movements with Plant Growth Patterns.

In the summer, caribou primarily consume lichens, but they also eat dried sedges and small shrub leaves, like blueberries. Plants contain a wide array of nutrition that vary seasonally and by plant species. The time of year and available nutrition influence what specific plants caribou need. In the summer for example, they bulk up on nitrogen-rich greens—plants with fresh leaf growth—which help them persist during the long winter with limited nutrition. In later months, they will shift feeding habits to take advantage of the fresh growth of willows, sedges, flowering tundra plants and mushrooms.

Caribou Roaming Across Field - Alaska - Lois Epstein
Lois Epstein
6. Large Herds are Safer Against Things that Bite: Predators and Mosquitos.

A young caribou alone with its mother is much more vulnerable to predation than a group of calves surrounded by many adults. But wolves and bears aren’t the only concern for caribou. Mosquitoes, while tiny, are more than a nuisance and are a seasonally devastating force to mammals in the Arctic. A single caribou in the Arctic tundra, for example, would have no chance of reprieve from the dense, thick swarm of mosquitoes attracted to it. A massive group of caribou, on the other hand, allows the same swarm of mosquitoes to disperse and prey on thousands of caribou. The same holds true for black flies and oestrid flies—parasitic flies that lay eggs under the skin and in the noses of caribou which cause painful, infected sores.  

7. Newborn Caribou Calves Can Outrun a Human at Only a Few Days Old.

Caribou enter the rut, or breeding season, in October. After a gestation period of 230 days—7.5 months—calves are born by early June. Caribou calves are precocious, meaning as soon as they hit the ground they begin stumbling, then walking, and after only a few days on the tundra, are capably running with the adults.  

Caribou and Calves crossing a river at National Petroleum Reserve Alaska
Subhankar Banerjee
A herd of caribou with calves cross the Kokolik River at National Petroleum Reserve Alaska.

While there is safety in numbers, many calves are lost to predation in the first week of life when they are most vulnerable. In healthy, intact ecosystems, approximately 50% of calves succumb to predation each year.

8. Caribou Are the Only Ungulate Species Whose Males and Females Both Produce Antlers.  

Females drop their antlers shortly after giving birth, while mature bulls usually drop their antlers after they have mated with females. Young males might keep their antlers as late as March. A few caribou, 3% to 5%, won’t grow antlers at all throughout their lives.

Antler Bonus Fact

How to Help Caribou

Worldwide, populations of caribou and reindeer have dropped 56% in the past two decades. Support caribou herds by applauding the cancelled leases on the Coastal Plain of the Arctic National Wildlife Refuge where the Porcupine Caribou Herd calves each year. Stay informed by following the progress of Defenders of Wildlife’s active court case against Conoco Phillips’ Willow Project that cuts through the Teshekpuk Caribou Herd’s migration route in the National Petroleum Reserve-Alaska.  

In May 2024, the Bureau of Land Management took steps to conserve critical wildlife habitat, including caribou habitat, and added more robust protections to the five designated “Special Areas” across the National Petroleum Reserve. Watch for an opportunity to help conserve caribou habitat provided by these regulations this summer.

Buckle up, we're virtually hitting the road this summer! Learn about the other amazing species in Alaska we are fighting for and check out cool places you can visit during your next trip to the state. 


Christi Heun

Christi Heun

Alaska Senior Representative
Christi Heun works on Arctic issues and Tongass National Forest restoration efforts. She works with Tribal partners and state and federal biologists to serve as a terrestrial mammal specialist supporting efforts to protect species like caribou from large oil and gas developments in the Arctic.

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Caribou in Denali

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