
Subject: How They Survive
Summary: How do plants, birds and mammals survive the harshness of the winter,
  and what activities could you have on this theme -- localized to north-
american
  fauna and flora



How They Survive
Ben Kruser
The Leader, December 1985


The absence of concealing foliage during winter presents the
opportunity to discover wildlife habits and happenings that occurred
during warmer months. Bird and insect nests appear where we were sure
no animal could hide.

Winter also opens the door to discovering how wildlife copes with
extreme cold. By studying different survival schemes, we learn some
good lessons about environmental adaptations.


Plants

Do plants migrate? Why is sap stored in the roots? How do plants avoid
drying out when they are exposed to cold, arctic winds?

Once a plant is rooted, it must contend with changing environmental
factors. Plants do migrate, in a sense, by dispersing seeds that,
given the right conditions, will germinate in far-away areas.

Plants that overwinter in the mature stage face moisture-related
problems. The cactus is adapted to desert conditions that are similar
to the winter environment. To conserve precious water, it has a small
surface area that cuts the number of pores exposed to moisture-wicking
wind. Cactus leaves are tightly rolled into spines that serve double-
duty as armament. A waxy coating covers the cactus body to seal in
moisture as well.

The life-preserving water inside the cactus becomes life threatening
in winter. Stored sap expands as it freezes and can burst cells and
damage the plant. To prevent this, the cactus expels its water and
overwinters as a limp deflated pincushion.

Deciduous trees also reduce their pore surface area for winter by
shedding their leaves. Evergreen needles with their small size and
waxy coating enable the tree to grow on poor soil and in colder
habitat zones. To prevent damage from the freezing of the stored
water, tree sap flows away from extreme freezing temperatures into
deep roots.

Rhododendrons are evergreens that retain broad leaves throughout
winter. On cold, windy days, the leaves will droop and furl to cut
exposure to the wind, an adaptation similar to that of the cactus in
winter.


Insects

Where do insects live in winter? Some insects, such as monarch
butterflies and dragonflies, migrate south. Most insects only live
until fall and pass on their legacy by laying eggs that will hatch the
following spring.

Examine the branches of fruit trees such as cherry and apple for the
small, thick, bubbled band of the tent caterpillar's egg case.
Although the case is coated with an impervious chemical-resistant
shellac, you can easily prune or peel it off to prevent infestation.

Some moths and wasps overwinter in the larval stage. Look under the
bark of dead trees or logs. Silky cocoons protect the pupae from the
elements, but not from the prying beaks of hungry chickadees,
woodpeckers and titmice.

Midges, sawflies and certain wasps have adapted to letting plants
build cocoons for them. The adult injects an egg and some body fluid
into a host plant. The fluid activates woody tissue around the egg to
grow rapidly. The result is a thick, bulbous gall. In spring, the now
mature insect chews a hole through the plant tissue and begins the
cycle anew.

There are numerous types of galls. Open and examine for larvae small
"oak apples" attached to oak leaves. Pine-cone-like growths on willows
are aptly called pine cone willow galls. Tumors on goldenrod stems are
goldenrod ball galls. A goldenrod bunch gall results when a gall midge
lays its egg on the tip of the plant's stem. Although the stem stops
growing, the plant continues to produce leaves and the result is a
rosette.

Tumors on elm, oak and pine trunks, called burls, are signs of a
bacteria or virus infection.

A gall has some advantages over a cocoon. It offers more camouflage
and resistance to predators than some cocoons. Red squirrels, however,
favour white pine blister-rust cankers and cottonwood leaf galls.


Amphibians

How do cold-blooded animals keep from freezing solid? How can they
breathe when they're buried in mud? Researchers looking for answers to
these questions ran experiments on three cold-resistant frog species;
the spring peeper, wood frog and gray tree frog. They froze the frogs
at -6 degrees C to -12 degrees C for a week, then exposed them to
temperatures between 8 degrees and 10 degrees C. After three days, the
frogs had fully revived.

Insects and amphibians are able to survive freezing because their
bodies produce glycerol, a glyxol alcohol compound we use in the form
of car antifreeze. The substance circulates through their blood and
prevents their vital organs from freezing up. As the body temperature
drops, their metabolism slows and they need less oxygen to maintain
body functions. Wintering frogs require only a fraction of their
normal oxygen intake and are able to absorb sufficient quantities
through the skin.

Animals without glycerol, such as snakes and turtles, have limited
northern ranges because of their low tolerance to sub-zero
temperatures and inability to reproduce quickly in a short breeding
season.


Mammals

Why do animals hibernate? What special traits do hibernating mammals
exhibit? Do they use glycerol too?

Hibernation is a specialized adaptation which allows animals to
survive in times of extreme environmental conditions or food
shortages. Some species of desert ground squirrels will enter into a
state of torpor during hot dry months. This is called estivation.

Hibernating mammals do not use glycerol. Instead, they build up a
dense layer of brown fat and rely on a body-produced chemical called
HIT, the hibernation induction trigger.

White fat does not burn off readily and acts as an insulator. But,
when a hibernator's body temperature drops too low, stored brown fat
does "burn" to create body heat.

As the days grow shorter and colder, the hibernator's brain begins to
produce HIT. The chemical induces a deep sleep and regulates the
lowering of body temperature, heart beat and breathing. HIT also
guards against infections and diseases during hibernation.

In the golden-mantled ground squirrel, the heart slows from 350 beats
per minute to three or four. Body temperature drops from 37 degrees C
to just above 0 degrees C. Contrary to popular belief, ground
squirrels, woodchucks, bats and dormice do not sleep for five months
straight, but wake periodically to nibble on stored food. During
hibernation, there is virtually no body-waste build up.

Bears, skunks, raccoons and tree squirrels are not true hibernators.
Black bears enter into a hibernation-like state of lethargy where the
body temperature drops from 38 degrees C to 31-34 degrees C and their
breathing rate to only three or four times a minute. But they are
easily awakened from their sleep.

How do non-hibernators adapt to winter conditions? Food caches are
handy, but heavy snows can bury them out of sight. Many winter mammals
have an excellent sense of smell. Caribou can scent lichens under a
heavy snow crust and use their broad hooves to dig feeding craters.
The word caribou means "the one that paws". Researchers have found
that gray squirrels can smell their buried acorns through 100 cm of
snow.

Specialized hair helps some animals to repel cold. Deer hair is hollow
and the dead air space retains body heat. The long guard hairs of a
wolverine protrude well above the dense underfur to shed any ice or
frost buildup. Oily hairs on the foot pad prevent snow from balling
around hooves and paws.

A white fur coat has obvious camouflage benefits and, now, biologists
who study polar bears believe it offers an added solar radiation
advantage as well. The lack of pigmentation allows the hair to perform
like fibre optics to carry sunlight to the polar bear's black hide by
internal refraction. In this way, the skin is provided extra warmth.

Birds

Birds migrate for the same reasons mammals hibernate - to escape
environmental pressures. Some species of swifts hibernate when cold
weather kills off their insect food. The poor-will of the southwestern
U.S. lowers its body temperature to 6 degrees C and can endure almost
90 days without food.

Winter birds use similar schemes to those of winter mammals to cope
with frigid weather. Stiff feathers around the toes of the sharp-
tailed grouse act as snowshoes. To accommodate an increased demand for
oxygen as the temperature drops, the rock ptarmigan has a heart four
times bigger, compared to body size, than that of a ruffed grouse.

Before winter sets in, birds grow an added layer of air-trapping adult
down. This fluffy long-john suits the arctic dwelling willow
ptarmigan. Its winter plummage is so effective against cold that, at -
13 degrees C it needs only the same amount of energy to maintain body
heat that it uses at 32 degrees C. By digging a burrow into an
insulating snow bank, the ptarmigan can conserve its precious layer of
body fat.

Winter foods are very important.

High energy berries such as highbush cranberries, and rosehips are
rich in carbohydrates and vitamins. Insects are almost total protein.


Actvitities 

Collect and make a display of insect galls. Put some in a glass jar to
capture the emerging adult. Look for old white-faced hornet (paper
wasp) nests in trees or on buildings. Examine them for dead wasps and
note their characteristics. Can you find any coloured flakes in the
nest material? Wasps will sometimes take paint flakes from nearby
houses for building material.

Bird nests also give clues to wildlife behaviour. Can you find
evidence of food and eggshells? What was the favourite nest building
material? Do not remove the nest, since it is protected by law as are
the birds. One of the reasons for this protection is that returning
migrants can re-use the nest. This means birds can begin breeding
sooner and the young have longer to develop before having to begin the
fall migration.

Discuss the similarity and differences between how various animals
survive and how man survives. Why are wool and down coats better
insulators than nylon? What hardships did frontier explorers face when
travelling in Canada's high arctic? A study of nature's adaptations to
cold will give us insight on how we can live in harmony with the
natural world.


Resources

American Nature Study Society Newsletter, Teaching Tips - Winter
Outdoor Studies; 6(1), 1985.

The Mammals of Canada by A.W.F. Banfield; University of Toronto Press,
438 pp., 1974.

Cacti in Canada by Elliott and Nicole Bernshaw, Nature Canada 13(3),
pp 22-27, 1984.

Ptarmigans, Hinterlands Who's Who Series, Canadian Wildlife Service
1974.

Arctic Ordeal, The Journal of John Richardson, Surgeon-Naturalist with
Franklin, 1920-1822 by C. Stuart Houston, McGill-Queen's University
Press, 349 pp., 1984.

Some Plant Galls of Illinois by Glen S. Winterringer, Illinois State
Museum Story of Illinois Series, No.12; 1971.
