Almost everyone knows that birds fly south for the winter. Even those who have no interest in nature have heard of this phenomenon in songs, poems or common folklore. But few are familiar with the concept of vertical migration, the seasonal movement of birds and mammals in mountainous areas.
Rather than changing latitudes, many mountain residents adapt to the seasons by altering the elevation of their residence. Heavy snows and severe winter weather can impair the survival of mountain dwellers and they have thus developed the instinct to move on to lower terrain as the days shorten. Elk, mule deer and bighorn sheep adhere to this pattern, as do the carnivores (mountain lions, wolves and coyotes) that prey on them. The same is true for a number of mountain birds; an exception among Colorado birds is the blue grouse, which summers in the footills but winters in the higher mountain forests.
Contrary to popular perception, winters are relatively mild across the Front Range urban corridor. Though overnight lows often drop into the teens, January highs are usually in the low 40s (in contrast to the low 20s across the Upper Midwest); combined with abundant sunshine and modest winter snowfalls (the heaviest snows arrive in early spring), the region is downright balmy when compared to the mountain conditions. Our Littleton farm, which sits at 5400 feet, welcomes a number of mountain migrants each winter; among them are Townsend's solitaires, red-breasted nuthatches, dark-eyed juncos (gray-headed race), Cassin's finches, pine siskins, mountain chickadees, red crossbills, golden-crowned kinglets and yellow-rumped warblers.