Autumn comes early to the high Rockies. As early as August, plants and animals begin to prepare in various ways for the coming cold, snow, and high winds of winter. In essence, organisms can either settle in for the winter or flee to warmer climes, and if they stay, they can either sleep the winter away or stay active.
The pika (Ochotona princeps), for example, spends a busy winter under the deep snow above treeline eating “haystacks” of grasses that it harvests during the brief summer. The yellow-bellied marmot (Marmota flaviventris), on the other hand, drifts into a true hibernation, during which it can lose up to half its body weight. In late summer, marmots begin storing fat. They hibernate from September or October into April or May.
Animals don’t always survive hibernation. Recent research shows that mammals that eat human handouts during the summer are less likely to survive hibernation because the quality of fat stored is not as high as that on a natural diet. Another good reason to not feed the animals!
Among trees, the conifers (spruce, fir, pine, and Douglas-fir) retain their leaves, which remain green throughout the winter, but much of the plants’ summer activity is shut down or decreased. Photosynthesis stops except for uncommonly warm, sunny days. Intricate molecular changes allow these species to keep photosynthesis in a “dormant” state but geared up and ready. If conditions permit, photosynthesis and other functions can be started up quickly to take advantage of the favorable state of affairs. The broad-leaved trees, however, drop their leaves - usually after a brilliant show of fall color - and become dormant until longer spring days waken them to start producing leaves – their photosynthetic organs.
Birds have mobility that the earthbound can only envy. But, while many species flee to warmer climates, some remain and do well either by finding a niche in the cold or by migrating down to nearby parks, fields, and lawns as the weather changes. The mountain chickadee (Poecile gambeli) for example, spends the winter in the park or in nearby lowlands. At the other extreme, the broad-tailed hummingbird (Selasphorus platycercus ) migrates to Mexico and Central America before returning in spring.
While winters can be long and hard in Rocky Mountain National Park, the plants and animals who live here use a variety of strategies to persist from year to year.