Beavers (Castor canadensis) are large (up to 40 pounds), brown, aquatic (water-living) mammals. Two of their most distinctive characteristics are their large orange teeth that continue growing throughout their lives, and their flat, black, scaly tails. They are active all year long, and breed between January and March. Pairs mate for life. Gestation takes about 107 days and usually a litter consists of two or three kits. Young beavers stay with their parents until they are about two years old, and help with food collection, dam construction and repair, and care of kits. Beaver colonies usually consist of about five or six animals- the adult pair, yearlings, and kits. Beavers eat both woody and non-woody plants. They prefer non-woody vegetation, but store large quantities of aspen and willows for winter consumption when non-woody plants are not available.
Beavers are considered by many to be "nature's engineers," because of their dam building activities. Scientists regard them as keystone species - those that modify the environment in such a way as to encourage the presence of other species. In the case of beavers, their propensity to build dams and thus create or expand wetlands, dramatically altering the landscape, encourages a multitude of other aquatic species. Beavers are most frequently associated with streams in the park. They generally prefer areas that are not particularly steep, with a stream gradient of less than 6%, and are not known in Colorado to inhabit areas with stream gradients of more than 15%. A 1% gradient represents a decrease in altitude of one foot for every 100 feet of distance.
Predators of beavers in Rocky Mountain National Park may include coyotes, wolverines, bears, otters, hawks, owls, and eagles. Most of these predators take kits, although coyotes can take adults. Beavers are also susceptible to diseases. Two beaver found dead in the Park during the past 10 years tested positive for tularemia, although recent testing of beavers in the park indicates this is not a widespread problem.
Beaver populations have declined in many areas of Rocky Mountain National Park for the past 50 years. Recent beaver surveys have documented about 15-20 active beaver colonies in the park. Populations in the past 10-20 years have remained low, despite some apparently suitable sites for dispersing beaver. Research in the park continues in an attempt to determine what is keeping beaver numbers low, and how beaver modify the park's landscape and hydrology where they are present.