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Behavioral Adaptations: Migration

Q. Does the Porcupine caribou herd migrate?
For centuries this herd of caribou has migrated from its summer calving and feeding grounds on the coastal plain of Alaska and the Yukon south to winter in the mountains and valleys near the Brooks Range.

Q. What is their migration range?
The Porcupine caribou is a barren-ground caribou herd whose range is large- over 250,000 square kilometers. The range extends from northeastern Alaska across the northern Yukon to the Makenzie Delta in the Northwest Territories. The herd winters in the boreal forest of the Richardson and Ogilvie mountain ranges.

Q. How far will the caribou travel in a year?
The migration route can take them over 800 miles (1300 km) distance each year.

Q. What makes the Coastal Plain a good place for calving?
The full reason the herd returns each year traditional calving grounds is not fully understood. However, it is likely that they choose these areas because spring vegetation appears here first. These areas also offer better protection from predators and insects.

Q.How do winter snowstorms affect the caribou?
Believe it or not, caribou don't like deep snow. Caribou feed on lichens under the snow and tend to occupy areas with favorable snow conditions. Favorable areas for digging feeding craters have snow depths of less than 50-60 cm (20-24 in) and densities of less than 0.34 g/cm. Big snowstorms make it difficult to find food.

Q. Do they travel in herds or as individuals?
Because caribou need to be able to both watch for predators and eat at the same time they most often are found in herds. Barren-ground caribou form different kinds of herds at different times of the year. Starting in early September larger groups form and continue through fall migration. In winter, bull caribou may avoid groups of cow caribou and their calves because they know that preditors are drawn to the more vulnerable young caribou.


Q.What do Porcupine caribou eat in the winter?
Caribou are herbivores. The main component of the winter diet is lichens. Next is the evergreen low-bush cranberry shrub. They also eat moss, grasses, equisetum and other small shrubs. Caribou have to dig holes in the snow (called feeding craters) to find these plants. Caribou seek areas of reduced snow cover, south slopes and windswept mountain ridges to locate winter food supplies.

Q. What do Porcupine caribou eat in the summer?
In late May when the caribou reach the calving grounds on the coastal plains, lichens and lowbush cranberry are the most important componentw of the diet as well as moss. In early to mid-June cottongrass becomes an important food. Once willow leaves emege in late June, caribou quickly shift their diet. Other green leaves this time of year, including dwarf birch and bluebery are also eaten. They sometimes eat mushrooms when they are available.

Q. How much do they eat in a day?
Barren-ground caribou are grazing animals and the average caribou eats over 3 kilograms of vegetation a day.

Q. What is a lichen?
Lichens are plants made up of an algae and fungi growing together. The fungi forms the body of the plant and the algea cells produce energy through photosynthesis. They can live to be many years old.


Q. What is the caribou habitat?
Caribou, like all animals need food, water, shelter and space. The area where these requirements meet is called habitat.

Q. What are the caribou's critical habitat areas?
These areas include safe places to have their calves, areas where they can find relief from summer insects, access to favorable migration routes where they can safely travel, and access to winter range land with low snow depths so they can obrain their food.


Q. What are the caribou's main enemies?
The main enemies of the caribou are animals that prey on them (predators), and also sickness, disease, parasitism and other factors relating to calf death.

Q. What are the predators of the caribou?
Golden eagles who are non-nesting sub-adults are the most important predator of the calves on the calving grounds.They kill the calves with their talons. Wolves can be an important predator of adult caribou in the winter. Grizzly bears are found on both the summer and winter ranges of the Porcupine caribou. Wolverine are capable of killing a newborn calf or a cow giving birth. They also will take a sick or dying caribou. Blood-sucking insects are often called "micro-predators." Both mosquitoes and black flies bite persistantly and can prevent caribou from feeding, calves from nursing and even cause injuries by caribou rushing wildly about. Foxes, ravens, owls,haegars and hawks are other carrion eaters or scavengers that feed on caribou kills.

Q. What do we know about caribou sickness, disease and parasitism?
Information about sickness, disease and parasitism is very limited. We do know that diseases and parasites are not thought to be significant factors in the general survival of the caribou. Parasites consist of a variety of worms and microscopic one-celled animals and insects that spend all or part of their lives inside the caribou.

Q. Porcupine caribou are affected by 2 kinds of flies. What do we know about the Warble and Nosebot flies?
Warble flies can cause caribou a lot of irritation. About the size of a small bumblebee, the flies cause caribou to run wildly about to the point where they can lose considerable amounts of the weight they have gained in the warm summer months causing them to go into winter with less fat reserves. The flies lay eggs on caribou and live inside the animal until the following spring when they exit through the back of the animal as larvae. Nosebot flies also cause panic within the caribou herd, too. They hover and dart about the animals landing on their faces. The fly deposits it's larvae near the caribou's nostrils. Larvae crawl up into the nasal passages of the caribou where they live for many months and exit as larger more mature larvae. If the concentrations of these larvae become too great the caribou can have difficulty breathing which can weaken the animal.

Q. What about fire?
Generally fire is a friend to caribou habitat. The vegetation, birds and mammals - including the caribou depend on the fires of the northern boreal forests to replenish and nourish their growth. Desirable and important species such as willow and reindeer lichen are rejuvenated and made more palatable to the caribou after the fire.

Q. What kind of impact do humans have on caribou?
For thousands of years native people have hunted this caribou herd. Early hunting weapons and strategies changed dramatically with the arrival of Europeans. Significant changes came about with the arrival of the whalers in the 1800’s when caribou were needed for provisions. Later, fur traders, trappers and miners took more of the caribou harvest. Since the development of snow machines and high-powered rifles human hunters have become a significant source of mortality on caribou.
In addition, the building of roads and discovery of oil throughout the migration range have brought on additional challenges for management of the herd.

Q. What is involved with conservation of the herd?
Conservation of the Porcupine caribou involves wise use of the caribou as a resource of food and traditional culture for the Vuntut Gwitchin and protection of its habitat. The Vuntut Gwitchin, a First Nation tribe depends heavily on the Porcupine caribou, a source of food and other products that has sustained them for thousands of years. In recent years, intended oil exploration and development in the area has threatened the herd's calving grounds. In spite of their small population and limited resources, the Vuntut Gwitchin have taken on the United States government successfully to protect the traditional calving grounds of the Porcupine Caribou.

Q.Why does the Arctic National Wildlife Refuge play an important role for conservation of the herd?
The coastal plain of the Arctic National Wildlife Refuge has been the calving grounds of the Porcupine caribou for centuries. The coastal area provides rich vegetation, harbors few predators and offers wind of the Beaufort Sea to keep insect pests to a minimum for the calves and cows.