Migration is one of the key strategies animals use to cope with Colorado’s harsh winters. When we think of animals that migrate, many of us think of flying creatures. The return of the hummingbirds is always a welcome sign of spring. The journey monarch butterflies make from all over North America to their breeding grounds in Mexico each winter is incredible, especially considering the size and fragility of a butterfly. And of course, grandparents across the northern reaches of the country, from New Jersey to Chicago, don metal wings as they flee the winter weather for sunny beaches and deserts of the south.
But animals without wings (or access to jet planes) make migrations as well. The vertical relief in Colorado means the state has numerous microclimates in a relatively small geographic area. Our famous 250 days of sun also means that hillsides with a southern aspect may offer vegetation, browse, and ease of travel that would be impossible on northern aspects that retain feet of snowpack all winter and well into the spring. Humans have noticed these differences and built most of their ski resorts facing north to shade them from the sun as it arcs across the southern sky in winter.
This variation in aspect can be the difference between life and death for Colorado animals that cannot travel thousands of miles to warmer climates. Large herbivores like deer and elk take full advantage of differences in aspect and elevation to survive the winter. They conserve energy by frequenting drier hillsides where there is less snow to trudge through. The shallower snow leaves vegetation exposed for food as well. Winter is a dangerous time of year for animals that do not have a wood stove to warm them and a grocery store to import fresh produce all year long. In a harsh season many deer and elk may barely scrape through the winter, finding just enough food to barely meet their energy demands and surviving off stored fat from the past summer.
Fortunately, the deer and elk that have made it to the month of May are likely in the clear. Flowers and grasses are sprouting and turning green again. As the weather warms, the large herbivores will follow the bloom uphill as spring reaches higher elevations. They will shed their thick winter coats but will still be more comfortable this summer in the shade and in cool, high mountain meadows than they would be in the arid scrublands and on southerly slopes where they took refuge for the winter.
This seasonal migration has been going on for millennia. It certainly occurred long before European settlers ever visited Colorado. The Ute Indians, who primarily survived on subsistence hunting, gathering, and some agriculture, learned to follow the migration paths of Colorado’s other large mammals long ago. Now that the population of Colorado has burgeoned above 5 million, the elk and deer probably benefit by retreating further from low-elevation population centers as well.
For humans interested in seeing some of these animals on the move in large herds, now is the time. In spring, animals who will only be active at dusk and dawn in mid-summer are actively grazing all day long as they try to make up the energy deficit they ran during the winter. While spring is here and summer is an easier time for these large mammals, winter is only a few months away. Especially for animals born this spring, time is scarce to fatten up and get healthy for another challenging winter.
Peter Wadden is the Landscape Stewardship Coordinator at Walking Mountains Science Center. He would like to encourage you to be aware of wildlife on and near the road during their spring migrations.