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Northern Exposures

Surviving the Arctic Tundra: A Look at Cold-Weather Adaptations
by Jeff Brune

To keep warm on a cold day, you might pile on lots of clothes or have a cup of hot chocolate. The nose bot fly of the frigid arctic takes a decidedly different approach to staying warm. It takes refuge in the warm, steamy nose of a caribou. Once in the nostril, the fly withstands the snorts of the irritated caribou and quickly deposits its wormy offspring. The maggots then crawl through the caribou's nose passages and settle in its throat, where they spend the winter warmed by the caribou's body heat and feed off its tissues.When spring arrives, the well-fed maggots are coughed up or sneezed to the ground,where they turn into adult flies, and begin the cycle all over again.

Snow GooseSnow Goose. Attracted by plentiful food, endless hours of daylight in which to eat, and a comparative lack of predators, snow geese and many other migrating birds flock to the tundra during the summer months.

Keeping warm is no easy task on the arctic tundra when winter lasts almost nine months of the year and where temperatures can plunge to -55C. Even during the brief summer, when the land thaws and the sun never sets, a sudden snowstorm can freeze everything. Constant high winds rob the environment of moisture and have a sandblasting effect; propelling sharp ice crystals and gritty dust that would tear a common house plant to shreds.When the growing season lasts only 10-14 weeks and the soil has few nutrients, its not easy for plants to make food. Similarly, when the sun sets for more than two months and the only light to hunt comes from the moon or the eerie shimmer of the northern lights, animals have a hard time finding sustenance.

SaxifrageSaxifrage. Like many arctic plants, saxifrage grows low to the ground, where it absorbs heat radiated from the soil in the summer and is protected from winds and wind-borne ice by a blanket of snow in the winter.

Despite such difficult conditions, life manages to survive in the arctic.Because the plants and animals that live there have special traits, or adaptations, that make them especially suited for the cold, the persistent wind, and the brief growing season. These unique adaptations can be physical traits (such as warm fur), behaviors (hibernation), or physiological traits (such as the chemical processes that allow certain arctic plants to make food in low temperatures).

Keeping Warm
Life forms on the tundra have devised many ways of dealing with the arctic chill.
Many animals avoid the cold altogether. Millions of birds that flock to the tundra during the summer months fly south to warmer climates during the winter. Vast herds of caribou also leave the tundra in the winter and head for the protective cover of northern forests, although some caribou remain on the tundra through the winter months.

Brown (grizzly) bear. Thick fur insulates this bear from the coldand affords it some protection from insects in the summer. Hibernation and a willingness to eat just about anything help the grizzly to survive the arctic climate.
Brown Bear

The hardy residents that stay in the arctic year-round have developed special adaptations to brave the chill. Musk ox, for example, have two layers of protective fur. The outer layer is made of long hairs that protect the animals from wind and water. The woolly inner layer of fur traps air next to the body. Body heat warms the air, keeping the musk ox cozy warm even at -40 degrees C! Other furry animals include brown bears, caribou, wolves, ground squirrels, foxes, and hares Even birds have responded similarly to the cold, developing thick layers of feathers. The willow ptarmigan, for example, has water-repellent outer feathers in addition to inner feathers. These birds, which live year-round in the arctic, even grow feathers on the soles of their feet! These feathers keep feet warm and double as snowshoes to prevent the bird from sinking into the snow.

When fur or feathers are not enough to stay warm, some arctic animals seek shelter. For example, to escape the cold winter winds, the willow ptarmigan takes flight and dives into a drift of soft snow. The snow blankets the land and acts as a good insulator, trapping heat that comes from the ground. Diving from the air, the ptarmigan leaves no tracks for predators to follow.

Marsh MarigoldMarsh marigold, nose bot fly, and mosquito larvae. The marsh marigold's bowl-shaped flowers follow the sun and focus light in toward the pollen and seed portion of the plant. Like all insects, the nose bot fly is cold blooded and often warms up by basking in flowers. Mosquitoes take advantage of the tundra's large areas of standing water to deposit their eggs. Once the larvae emerge, they immediately begin feeding on bacteria, microscopic plants and pollen.

Plants, shelter themselves from the arctic elements by growing low to the ground. In the arctic summer, dark-colored ground absorbs energy from the sun. So plants grow close to the warm ground, rather than tower above the ground. There is also more moisture near the ground away from the drying winds blowing above. In the winter, snow blankets and protects arctic plants from the wind and cold. In the winter, snow blankets and protects arctic plants from wind and cold. Any twigs that extend above the snow are slowly ground down by the sharp ice and snow blowing along the surface.

Insects battle the cold in many intriguing ways. All insects are cold-blooded and even on an arctic summer day, the chill in the air can make it difficult to move, let alone fly. So insects first need to warm up. Billions of mosquitoes, midges, gnats, crane flies, and hover flies warm up by basking in the sun often in the middle of a flower like the arctic dryad or arctic poppy.

Certain butterflies, such as the Polaris fritillary, spread their wings and point them at the sun like solar panels to collect heat. Bumblebees shiver their flight muscles to generate heat and trap the warmth in their velvety fur. While there are more than 20,000 species of bees around the world, only two kinds have adapted to life in the arctic, and both shiver. Amazingly, these busy bees can increase their body temperature as much as 15C above the air temperature! That means when it's freezing outside and most insects can hardly move, bees are out flying, to find nectar and pollen for their colony.

Arctic TernArctic Tern. These birds create their own "endless summer" by commuting between the Arctic and Antarctic, visiting each during periods of constant daylight.

Probably the most cold-hardy of all insects is the arctic woolly bear, a caterpillar which spends most of its 14-year life frozen solid. Even for a thumb-sized creature, this is no small feat. When body fluids freeze, they expand, form ice crystals, and damage cells and living tissues, most often killing the organism. The woolly bear combats the effects of freezing by producing special chemicals. During the fiercely cold arctic winters, these chemicals prevent ice from forming inside the cells of the caterpillar,even when ice forms in the space between cells, in the gut, and in the blood. This adaptation allows the woolly bears to withstand temperatures as low as -70 degrees C.

Tundra Adaptations

Investigation: Size and Heat
Biologists have noticed that many tundra birds and mammals are larger and have smaller appendages than do similar species living in warmer environments. Tundra hares, for example, are among the largest hares and have shorter ears and legs than do desert hares (called jackrabbits). Similarly, arctic foxes have shorter ears than do desert kit foxes. Even lemmings are larger and have smaller ears and tails than do most other mouse-like animals. Large size and short appendages are adaptations that reduce heat loss and resist the cold.

The amount of heat loss increases as the proportion of exposed surface area to body mass increases. Since that proportion is greater in small animals, they lose heat more quickly. An animal with long legs, ears, or a tail has more surface area than an animal of the same size that has shorter appendages.

However, in some cases, small size can be an adaptation for survival on the tundra. Why? A small organism can survive on less food than can a large organism of the same species. Shrews, the smallest of all mammals, thrive in the tundra of arctic Alaska.

Materials, Part 1: Each work station should have two laboratory-type thermometers; large and small containers made of the same material (two tin cans or two plastic jugs, for example); hot tap water; access to cold temperatures outdoors or to a refrigerator; the Adaptation Cards (This is on a separate page); and a posted set of instructions.

Materials Part 2: Each work station should have one pair of latex gloves; several rubber bands; two laboratory-type thermometers; warm water; graduated cylinders or beakers; two containers of at least 250 ml capacity; access to cold temperatures outdoors or to a refrigerator; the Adaption Cards; goggles; and a posted set of instructions.

Instructions: Part 1
Which will lose heat and grow cold faster, a large object or a small object? Test your hypothesis with the following investigation.

  1. Fill the large and small containers with hot water. Measure and record the water temperature in each container.
  2. Place both containers outside or in a cold place for 15 minutes. Again, measure and record the water temperature in each container.
  3. Find the difference between the starting and ending readings for both containers. Which container's contents cooled down more? Did your prediction match your results?
  4. Based on what you found out about the relationship between cooling and the size of the objects, do you think animals living in tundra environmental would be larger or smaller than animals living in warm environments?
  5. Using the Adaptation Cards, compare the sizes of the animals in each pair. Which animals are larger - the ones living on the tundra or the ones living in a warm environment? Which moose do you think would be larger, one native to Wyoming, or one native to Alaska? Try to find out if you are correct.

Instructions: Part 2
Which one do you think keeps your hands warmer, mittens or gloves? Test your hypothesis with the following investigation.

  1. While wearing goggles, close off each of the five finger compartments in one of the gloves. Be sure the rubber bands are tight. This will be called the "mitten." The other glove will be called the "normal glove."
  2. Measure and record the temperature of the warm water.
  3. Pour 250 mL of the water into the "mitten." Tightly close the top of the "mitten" glove with another rubber band.
  4. Pour 250 mL of the water into the "normal glove," so that water runs into the finger compartments. Close the top of this glove with another rubber band. Again, be sure to close it tightly so it won't leak.
  5. Place both gloves in a cold place (a refrigerator, or outdoors if the temperature is cold enough), near each other, but not touching. Wait 15 minutes. Pour the water from the "mitten" into one container and the water in the "normal glove" into another container. Measure and record the temperature of the water in both containers.
  6. In which glove did the water temperature decrease? How would you explain this difference? Next time it's cold and you go outside, will you wear mittens or gloves to keep your hands warm?
  7. Now, think about animals living on the tundra. The blood in their bodies is like water in the gloves. Their toes, ears, and tails are like the fingers in the glove. Considering what you learned from this exercise, which animal do you think would stay warmer in the tundra, one with long ears, toes, and tail, or one with short ears, toes, and tail?
  8. Looking at the Adaptation Cards, compare the appendages (ears, tails, toes, and so on) of the arctic animals to those of the warm-climate animals. Give a reason for the differences you observe.

 Teacher Wrap-up
In the first part of this investigation, students observe that the small container lost more heat more quickly than did the large container. Heat loss increases as the proportion of exposed surface area to body mass increases. Since that proportion is greater for the small container than for the large one, the small container loses heat more quickly. In the second part of the investigation, students observe that heat loss is greater for the glove than for the mitten. This is because the glove has a greater surface area than does the mitten.

The Adaption Cards can help students make the connection between their investigations and animals adaptations. Tundra birds and mammals are larger the have smaller appendages than do similar species in warmer environments and, therefore, retain heat better than their desert counterparts.

Finding Food
The menu of available food in the arctic changes with the seasons. The summer is like an all-you-can-eat buffet. The sun shines 24 hours a day and plants soak up the sun and grow rapidly. Tundra ponds thaw and become thick with water plants, insect larvae, and shellfish. Millions of ducks, geese, loons, gulls, sandpipers, and other migrating birds return, ready to nest, have young, and gorge themselves. Great herds of caribou also arrive from their winter homes to give birth and feast on plants. Wolves, bears, and other predators take part in the foodfest. And let's not forget the mosquitoes, sucking blood from any animal, large or small.

The winter menu, on the other hand, is bleak. There is little sunlight, plants are snow-covered, and the summertime crowds have left. The hardy, year-round residents are left to forage for what little food remains. Microscopic organisms, plants, and insects go into a state of dormancy-- so they don't need food. Because birds and mammals need to breathe, they can't go completely dormant. Animals like the grizzly bear and arctic ground squirrel hibernate instead. Hibernating animals become inactive, their breathing and heart rates slow, and they have little need for food energy beyond that supplied by stored fat. 

Kit Fox. A creature of warmer latitudes and less seasonal change, this fox's fur does not change color with the seasons. And, unlike the arctic fox, the kit fox's ears are rather large. For this animal, heat retention isn't desirable, and the more of it lost by radiating out from those ears, the better.
Kit Fox

Another food-getting adaptation is moving or migrating for food. This is the strategy of millions of birds that arrive in the summer when food is plentiful and leave in the dark winter, when the food runs out. The arctic tern, considered to be the world's greatest traveler, flies from the Antarctic Ocean near the South Pole all the way to the Arctic to spend the summer breeding and nesting.

Caribou also migrate. Living on the tundra during the summer, they feed mostly on grasses, sedges, birch, and willow. In the winter, many caribou migrate to the moist northern forests where they feed on lichen, a plant composed of fungus and algae.

Arctic Fox
Arctic Fox. Thick fur provides warmth for this acrtic resident, changing color from summer (red-brown) to winter (white). Compared to foxes that live in warmer climates, the arctic fox has smaller ears, minimizing loss of body heat.

Plants too, have adapted to the Arctic. They are able to make food faster, and at lower temperatures, than plants in warmer climates. The alpine saxifrage, for example, has leaves that survive the winter without shriveling up. Once the spring sun hits the leaves, they begin to make food for the plant right away, thus providing a clear advantage over plants that must wait for new leaves to break out and unfurl.

Producing and Protecting Young in the Arctic
Of course, there is more to life on the tundra than just keeping warm, finding food, and avoiding predators. Animals have to raise their young, too, and do so quickly, before the short summer ends.

Birds that migrate to the arctic have to find mates, build nests, lay eggs, hatch them, and feed their young to the point where they can fly -- all in 10-14 weeks! So why do millions of birds fly from all over the world to the Arctic? First, food is plentiful, especially high-energy foods like insects that young birds need. There are also fewer predators than in the south. And there's more "working hours," provided by the constant sunlight, for parents to feed their young.

Jackrabbit. This warm-climate creature stays the same color year-round because there is not much variation in its environment. Note the large ears; the more heat lost through radiation from the ears, the better.

No matter what the climate,it takes lots of energy to have young, feed them, and raise them. Because food can be scarce even in the arctic summer, most animals have adapted the ability to adjust the number of young they have, depending on environmental conditions. For example, if the snow remains in the spring longer than normal, food sources remain covered. Some migratory birds, such as geese and swans respond by laying fewer eggs or none at all. Meat-eating animals like arctic foxes, weasels, and snowy owls will produce fewer young when their main food source -- lemmings --is scarce.

Caribou and musk ox put on a lot of fat in the late summer, but not just to prepare for winter food shortages. These animals also need large amounts of food energy for the mating season and birth process. Males need energy for doing battle with antlers or horns in an effort to win mating rights. Pregnant females need energy to feed the developing fetuses over the winter, and to take care for the calves born in the spring.

Snowshoe HareSnowshoe Hare. This arctic animal congregates in large groups, which helps create confusion when the hares scatter before the onslaught of predators. The hare's large padded feet act as snowshoes, and its coat changes color from winter (white) to summer (brown) to camouflage it from predators. Small ears help it to reduce loss of body heat.

Even mosquitoes need energy to have young. To get that energy, female mosquitoes drink blood. In fact, most female mosquitoes found worldwide must have a blood meal before they can lay eggs. Arctic species, however, can lay at least a few eggs even if they can't get blood, because they build up enough food reserves for this purpose as larvae. Of course, these mosquitoes can lay many more eggs after a quick slurp from some unsuspecting animal. And slurp they do, by the billions. In just one week's time, a single caribou can lose two liters of blood to mosquitoes. The insects don't get off scott free, however; yellow jackets catch many mosquitoes on the wing and feed them to their grubs .

With the summer so short, most plants on the arctic tundra do not have enough time to make seeds. Instead, the plants spread vegetatively, without producing seeds. For example, some plants grow runners above ground or below ground that reach out and form new, separate plants. Others grow little buds that fall off, blow away in the wind, and start to take root once they land in a good growing spot.

Ground SquirrelGround Squirrel. Thick fur protects this squirrel from the cold during hibernation. Prior to hibernation, the squirrel stores food to be eaten in the spring before new plant growth appears.

Those plants that do produce seeds rely heavily on mosquitoes and other insects of the far north to facilitate pollination. Some plants, like the Pallas's wallflower and prickly saxifrage, use the high winds of the arctic to their advantage. At the beginning of summer, for example, the plant stalks are short. Once the seeds are ready, the stalks grow tall, pushing the seed pods up above the fall snow cover. The high winds blow the seeds over the slippery, crusty snow, sending them over a wide area.

Life in the Arctic goes on, despite the brutally tough conditions. Faced with bone-chilling temperatures, relentless winds, and dramatic changes in the seasons, life does one thing: It adapts.

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Last updated: 11-13-2009