Beavers, the largest rodents native to North America, measure more than three feet in length, and weigh up to 55 pounds, with a broad, nearly naked, flat tail and webbed feet. Their sign is familiar: dams, lodges, bank dens, canals, slides and of course gnawed stumps of aspen, alder, willow or cottonwood. It takes a beaver approximately 30 minutes to fell a 5-inch diameter tree. Beavers feed on the upper, tender branches, leaves and bark of trees. Many mountain ponds, willow thickets and meadows also are the works of beavers over time. Beavers are active year-round. Their ponds provide navigable water beneath the ice. No mammal other than humans has a great an influence on its surroundings. This is a "keystone species" in riparian communities; without them the ecosystem would change dramatically.
As abundant as beavers are today, it is difficult to believe that once they were on the verge of extinction, trapped for their under fur, which was used to make felt for beaver hats. In the mid-19th century, silk hats replaced beaver felt as a fashion, and that probably saved the beaver from extinction. But, before it ended, the beaver trade opened the mountains of Colorado to European exploration.
Beavers are fairly well protected from predators by their large size and aquatic habits. Mink eat some kits, and coyotes can capture a beaver waddling on dry land. Aside from that, floods may be the largest cause of death. Beaver in Colorado are managed as furbearers.
The beaver lives throughout Colorado in suitable habitat, although it is most abundant in the subalpine zone.
Beavers live around ponds and streams that are surrounded by trees.
Beavers feed on grasses and forbs in the summer, and bark in the winter. Beavers eat the upper, tender branches, leaves and bark of trees. They do not eat the inner wood.
The den houses a nuclear family: parents, yearlings, and four or five kits. A single litter of young is produced each year, born in the spring after about a four month gestation period.
By David M. Armstrong Department of Ecology & Evolutionary Biology Environmental Studies Program, University Museum of Natural History University of Colorado-Boulder