Calving Grounds - Caribou Activities


May to Mid-June

Female caribou return to the same calving grounds year after year. Each population or "herd" of caribou has its own calving area. While small populations of caribou often calve in mountains or forested areas, calves of large, migratory caribou populations like the Porcupine Herd are typically born in treeless tundra where there are few large predators. The calving grounds of the Porcupine Herd stretch for over 100 miles, from the arctic coastal plain of the Yukon Territory in Canada across the border into northeastern Alaska. Many nutritious plants grow on the tundra calving grounds, and insect pests like mosquitoes and warble flies are scarce at calving time.

Because Porcupine Herd caribou migrate toward their calving grounds from the east, many cows are forced to give birth in Canada if late snowmelt slows down migration. In normal years, however, the majority of calves are born farther west in Alaska in the Arctic National Wildlife Refuge, where there is generally more nutritious forage and fewer predators. Therefore, calves survive better when calving occurs in Alaska.

Caribou mothers give birth to a single calf. Females typically give birth for the first time when they are three years old, but very well fed and healthy cows may give birth at age two, and cows in poor condition may not start having calves until they are four years old. Well-nourished adult cows give birth every year, but more poorly fed cows may skip one or more years between having calves. Caribou calves are very precocious so they can run and follow their mothers within a few hours of birth. Nevertheless, young calves are vulnerable to predators such as wolves, golden eagles, and grizzly bears. Caribou milk is rich in fat and full of nutrients, so calves grow quickly. When they are about three weeks old, calves begin to eat some of the same nutritious plants as their mothers. By then, the calves are also big and fast enough to have a better chance of escaping from predators.

Return to A Caribou Year.