Caribou Migration

September 16 - 17, 2000

Normally, caribou arrive at the homestead in August. Sometimes they move on through and sometimes they stay for all or part of the winter. In 2000, moose season came and went. No one knew where the caribou were. September 15, there wasn't a single caribou on the mountain. September 16, there were thousands upon thousands. For only the second time in Dennis' memory, the main herd migrated right through the homestead, swimming in solid lines across the lake (photo) and swarming over the mountain like insects.

Caribou on a fine October day The caribou were still around in October. We watched a string of them attempt to cross what looked to be very thin ice. Suddenly, most of the group turned and ran back the way they had come. The lead bull had broken through the ice a long way from shore. We prayed as we watched his life-and-death struggle. He flung himself up onto the ice again and again, slowly breaking a path but becoming more and more exhausted. It took over an hour, but he finally made it to shore where he rested for a long time before moving on.

More recently, we enjoyed a warm, sunny, lazy day watching caribou in October. It was likely one of the few perfect days in a caribou's life. No bugs. No wind. No cold.

No need to hurry on.

Here are some interesting facts about caribou:

The caribou in the photos are barren-ground caribou in one of 13 large herds in Alaska. Alaska is home to more than a million caribou.
Caribou are a type of reindeer. One difference is both male and female caribou have antlers whereas only male reindeer have antlers.
Early miners brought domestic reindeer from Siberia for food. Some escaped and interbred with the caribou herds.
Caribou are almost always on the move. They range over 27,000 square miles and their routes of travel are unpredictable. They travel about 3,000 miles a year.
The main food for caribou is lichen. While wildfire increases moose forage, it destroys lichen mats, which may take up to 50 years to recover. Caribou avoid areas that have been burned.
Caribou normally lose about 5% of their body weight over the winter, though some individuals find enough food to gain weight in the winter!
Caribou mate in the fall. Calves are born in May or early June. All cows in a herd drop their calves within a few days of each other, swamping predators. Calves weigh about 15 pounds at birth and double their weight within 20 days. They walk within hours of birth and can outrun a person and swim across a lake within days. About 50 calves are born for every 100 cows. Twins are rare.
Caribou populations naturally peak and plummet. One variable is the weather during calving. If the weather those few days is harsh, most calves die and the population plummets. Heavy winter snow makes it impossible for caribou to dig deep enough to get food and can decimate caribou populations.
Caribou bulls have the largest antlers of any deer species relative to their body weight of about 400 pounds. Antlers grow new every year and are covered with velvet until fall. Bulls fight each other for dominance in the fall. Sometimes their antlers lock together and both die of starvation. Before winter, most antlers are shed, providing nourishment for small animals who eat them.
Caribou are especially adapted to cold. They have two layers of fur, a dense, woolly undercoat covered by long soft fur that is hollow and creates a dead air space. The hollow fur sheds snow and water. Caribou even have fur on their hooves and in their nostrils. Special bones in the nostrils allow frigid arctic air to be warmed by the animal's body heat before it enters the lungs.
Caribou hooves are broad and paddle-like. They can soften and spread to support the animals' weight in snow or soft tundra, or retract and become hard enough to cut into ice, depending on the situation.
The legs of caribou and moose are long and thin, with little fat. This enables them to walk through deep snow. How do they keep their feet warm? Their circulatory system is especially adapted to minimize heat loss. Arterial blood, originating in the animal’s core, is warm, whereas venous blood returning to the heart has cooled. In the animal’s legs, arteries pass right next to veins so venous blood can be warmed as it returns to the core in a kind of heat-exchange system. Arterial blood cools to near ambient (outside) temperature before it reaches the feet but the cell membranes of the feet have different fats that those in the body core and can tolerate the cold.
Caribou are thought to be the only mammals that can see ultraviolet light.