The North American beaver (Castor canadensis) is native to Colorado, and its role as both an environmental engineer and a keystone species has profoundly impacted the state’s ecology and history. Although their populations today are low, beavers continue to shape Colorado’s environments.
Ecology and Early History
Beavers are the largest rodents in North America, and the second largest in the world. On average, they weigh between forty and fifty pounds and measure about forty-eight inches in length. Active in riparian areas (near waterways), the semiaquatic animals have developed waterproof fur and flat, scaly tails that function as a rudder, help with balance on land, and act as a lever in dam construction.
The most environmentally significant activity beavers do is create dams. They use their large teeth to cut down shrubs and trees, which they use as building material. Beavers form nuclear families, and several families live together in a colony. Working together, these colonies interweave materials, creating complex and watertight structures. Beavers are resourceful creatures, and their methods for creating dams vary depending on water levels and available materials.
Beaver dams create ponds with stable water levels that perform a variety of functions. According to wildlife resource scientist Dietland Müller-Schwarze, the beaver pond is a “highway, canal, lock … escape route, hiding place, vegetable garden, food storage facility, refrigerator/freezer, water storage tank, bathtub, swimming pool, and water toilet.” Not only do the ponds create a suitable habitat for beavers, but they help create and expand wetlands, providing habitat for other water-loving animals. This is why beavers are regarded as a keystone species–a species that disproportionately affects its environment and alters its ecosystem.
Prior to European settlement, an estimated 60 million beavers ranged across much of what became the United States and Canada. In Colorado, beavers could be found up to heights of 10,500 feet. Over thousands of years, beavers have aggraded small river valleys in North America, dramatically altering water systems and shaping ecology. Beavers were considered very important by many Native American cultures over the centuries. For example, the Comanche prized beaver pelts and tied strips of beaver skin to their braids.
Westward Expansion and the Fur Trade
Together, beavers’ warm fur and Europeans’ fashion tastes spurred a demand for beaver pelts that lasted from the mid-sixteenth century to the mid-nineteenth century. With the destruction of beaver populations in eastern North America and the American acquisition of the Louisiana Purchase in 1803, the search for new beaver trapping grounds lured trappers westward to Colorado.
The Rocky Mountains proved a bonanza for the fur trade from 1822 to 1840. Mountain men, the name given to trappers in the Rocky Mountains, explored much of what was to become northern Colorado over the course of the 1830s and 1840s in search of beavers. As the 1830s progressed, and as beaver populations declined in other areas, the Colorado Rockies became the second-most-important trapping ground for the fur trade. Trappers and traders also became some of the first Europeans and Americans to settle in Colorado, driven by the abundance of beaver. By 1837, fur trading posts had been established all along the Colorado Piedmont. Beavers thus played a large role in opening Colorado to white settlement and exploration.
In 1840, mountain man Robert Newell declared the fur trade in the Rocky Mountains dead. The destruction of beaver populations throughout the Rockies, as well as domestic economic instability and global changes in fashion, had brought an end to the economic productivity of the trade. However, it was not until 1900 that Colorado lawmakers decided to restore the drastically low numbers of beavers in the state. State legislation then began to restrict beaver trapping to specific seasons.
Beavers are still a rare sight in Colorado and have never fully recovered from their nineteenth-century depletion, even declining in many areas since the 1940s. In Rocky Mountain National Park, beavers inhabit only 10 percent of suitable habitat. There are numerous reasons for this. Beavers are widely considered to be an inconvenience rather than an environmentally essential species. Even though the Rocky Mountain Fur Trade ended in the nineteenth century, beaver hunting has persisted, albeit on a much smaller scale. Under Colorado State Law, so-called nuisance beavers that cause damage to property can be killed or hunted. There is no limit on the number of beavers an individual can bag during the hunting season.
Lack of adequate riparian plant life, such as willows, in Colorado is also a major factor in the stagnation of beaver populations. These plants are both essential food resources for beavers and greatly benefit from the stable water levels engineered by beavers. Rising populations of elk and cattle in riparian areas over the last century have led to increased grazing, which in turn has stunted the growth of riparian plants. Limiting elk and cattle grazing has been proposed as a solution to low beaver populations.
Current Rocky Mountain National Park conservation and wildlife management plans do not directly focus on beavers. However, officials have taken beavers into consideration in the park’s “Elk and Vegetation Management Plan” of 2007. The plan states that once willow vegetation has resurged, natural recolonization of beavers may occur. The twenty-year plan also proposes that if natural recolonization does not happen, then reintroduction would be considered. This, however, has yet to happen, rendering the future of beavers in Colorado uncertain.