How might an environment change affect an animal's migration?

Winter is the most stressful time of year in the north for most forms of life. The key hardships are a lack of food and cold temperatures. However, don't let a reduction in activity appear as if there is nothing going on in the woods!

A lack of food occurs for at least two reasons, both related to low temperatures. The first reason has to do with a reduction in active plant life. Plants, of course, are the sources of nearly all food chains. The second reason has to do with availability. For many animals, food sources are buried under snow or ice. Deep snow is not a problem for all creatures. To field mice, it is a protective layer against most predators. To predators, deep snow means a time of going hungry.