Below Zero Activities

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Snow Place Like Home

Age: Grades 4 - 9
Subjects: Science, Art, Geology
Skills: examination, evaluation, comparison
Duration: two 30-minute periods
Group Size: any, divided into groups of four
Setting: indoors and outdoors
Conceptual Framework References: 1c, 2a, 2c, 4a, 4b, 5b
Key Vocabulary: subnivean, intranivean, carbon dioxide, oxygen, snow crystals

Objective

Students will be able to describe the subnivean (under the snow) habitat and how small animals and insects use it.

Method

Students dig a snow pit and examine the winter plant and animal community living there. Students then develop a visual presentation of their findings.

Background

Note: See also "Snow Way to Hide!".
Snow is a wonderful insulator. It prevents heat loss, and protects creatures, plants and tiny organisms living within it. Life in the intranivean (within the snow) and subnivean (under the snow) environments is snugly sheltered from winter winds and extreme temperatures. Nonetheless, this wintry existence does have its dangers.

In early winter, small animals such as mice and voles, hunt for food on top of the snow. However, when snow deepens to between 15 and 25 cm, these creatures retreat beneath the snowy blanket. For the rest of the winter, they live in the subnivean space just above the soil. This is the natural space that develops between snow and the ground when snow falls and softly drapes over plants, bushes, grass and other objects like a big, fuzzy blanket. In this insulated space, temperatures are much warmer. In fact, if the outside thermometer plunges to a frigid -40C, it may be a positively balmy -4C beneath the snow at ground level. (Knee High Nature: Winter by D. Hayley, P. Wishart.) In the dim and quiet subnivean space, small animals like voles are busy all winter, bustling through a network of tunnels, storing food or nibbling plant stalks. (Snow, by John Bianchi & Frank Edward.) Sometimes they meet "roadblocks" caused by the packed down tracks of vehicles or footprints. Then they must surface, scurry quickly over the obstacle and burrow down into the safe, subnivean space again. While they are hurrying over the snow's surface, small mammals are an easy target for predators such as owls or coyotes.

How can creatures breathe beneath the snow? There's lots of air in and between snow flakes. There can be as much as 97 per cent air in a fresh, dry snowfall. (Snow, by John Bianchi, Frank Edwards). In the subnivean space, there are also natural ventilation shafts to the surface provided by grasses, trees, and shrubs. Under some weather conditions, snow can block the movement of light and gases, such as oxygen (from plants) and carbon dioxide (from animals). However, scientists aren't just sure how or even if this situation can harm subnivean creatures.

Snow doesn't stay the same once it falls to the ground. In fact, the winter snow pack is constantly changing. All winter long, old snow crusts break down, new ones form, and fresh snow falls, depending on the wind and weather. You can actually see the history of winter in the different layers in the snow pack. -- (Life In The Cold: An Intro. To Winter Ecology; Peter J. Marchand, pg. 184.)

Winter can be tough on wildlife, but fall and spring are actually the most dangerous times for small mammals. This is when floods happen, or unexpected early or late freezes. Sometimes not enough snow falls, or sheets of ice form within the snow, cutting off air and wildlife tunnels. Strangely enough, with its relatively stable temperature, winter is often the easiest time for small subnivean dwellers.

NOTE: For further information, see "Winter Fun" article from Owl magazine, pages 120-121, ISBN 0-9919872-86-7, and "Winter: An Ecological Handbook", Halfpenny, J. C. and R. D. Ozanne (1989). Johnson Books.

Materials

small shovel or digging implement; magnifying glass; rulers and measuring tape; paper and pencils; thermometers; black construction paper; and a small area of undisturbed snow

Procedure

1. Discuss the subnivean world, and how snow can insulate. Brainstorm a list of animal and plant adaptations for winter survival. Hand out the materials.
   
   
2. Outside, dig a snow pit big enough to stand in (about 1 m x 1 m) in an area of undisturbed snow. Measure the dimensions of the pit.
   
   
3. Examine both the snow strata and the ground surface. Collect samples of plants (alive and dead) within both areas. Note any signs of animal life on the snow surface and in the subnivean space. This might include tunnels, tracks, scat, hair, feeding areas, etc.) Also record interesting snow conditions, like ice sheets -- which prevent air circulation -- and different types of ice and snow crystals. (Students may want to sketch crystals for identification later.) Can you distinguish and count the number of layers in the snow from ground level to the snow's surface?
   
   
4. From the ground, record the temperature of the snow every 10 cm. Push the thermometer well into the snow and wait for three minutes before reading.
   
   
5. In the classroom, draw and identify the plants, snow and ice crystals, and other samples.

Variation

1. Hypothesize on possible adaptations an animal must develop for winter survival in the subnivean space.
   
   
2. Research and compare the sub-snow communities of the forest floor versus a grassland or meadow environment.
   
   
3. Students role play a vole, mouse, or insect and describe why and how they develop their winter subnivean habitat.
   
   
4. Students examine the variations in snow and ice crystal types and discuss what may cause the differences.

Evaluation

Students make a wall chart or large poster illustrating a cross section of the snow. The poster may include descriptions and samples of each layer, including plants, insects, temperatures and animal signs.

Copyright 1998 by the Canadian Wildlife Federation.
All rights reserved.