Winter Food Paths at the Water Tower

Field Notes from the Water-Tower Grounds

Snow covers the grounds around a small town's water tower. From a public path outside the fence, a winter nature club watches a meadow vole and a red fox. The vole is a small animal that travels through tunnels beneath the snow. The fox walks across the snow and sometimes stops to listen. Club members want to compare the routes that food energy takes to reach these two animals.

The club has notes from several visits. In late summer, members watched grass plants growing in sunlight and producing seeds. Some seeds fell onto the ground. During a winter visit, members saw a vole eating fallen grass seeds beside a tunnel opening. On another visit, they saw a fox catch and eat a vole. These observations describe selected meals, not the animals' complete diets. Both animals may eat other kinds of food.

Grass plants use light from the sun to make food. Some of this food is stored in their seeds. Food contains stored energy, which animals can use for movement, growth, body repair, and keeping warm. An animal uses some food energy while it is alive. Some energy remains stored in its body and can be transferred when another animal eats it. An animal does not receive the full amount of energy that originally reached a plant.

The club uses boxes and arrows to model these transfers. A box names an energy source or receiver. An arrow points from the source toward the receiver. A sun-to-plant arrow represents light reaching the plant. A plant-to-animal arrow represents energy transferred through eating plant food. An animal-to-animal arrow represents energy transferred through eating another animal. The arrows do not represent the direction an animal walks or the direction sunlight makes a shadow.

The club's models follow selected food-energy routes. They do not show energy amounts, meal sizes, or how long an animal can run after eating. Members also record when an observation happened. The grass produced its seeds during warmer weather, but the vole ate fallen seeds during winter. The club must account for both events when explaining the food energy available beneath the snow.