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
Q. What makes the Coastal Plain a good place for
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
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
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
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.
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