When greeting people in the open space, most aren’t very excited to talk about plants, and some are excited about birds, but nearly everyone is excited to talk about the larger mammals that can be found there. These days, in the summer of 2021, the talk is all about beavers!
A Bit about Beavers
The beavers in Colorado are American beavers (Castor canadensis). Beavers are among the largest of living rodents; in Colorado they can get to more than 50 pounds.
Beavers are adapted for an aquatic lifestyle. They have webbed hind feet, a paddlelike tail and their small eyes have a transparent inner lid designed for seeing underwater. Their fur is two layers – an outer layer of long shiny guard hairs which they oil to keep waterproof and an inner layer of dense, softer underfur to keep them warm.
Beavers are highly social animals, living in family (or extended family) colonies. A colony typically consists of adults and their yearling and juvenile offspring, known as kits. The adult female is the dominant family member in many activities, including constructing and maintaining the lodge, building the food cache and maintaining dams. Young animals typically leave the colony at 2 years of age, at the time of birth of a new litter.
The generally create their own pond by blocking a stream with a dam constructed of logs, sticks, rocks and mud. Long curved incisor teeth, strong because they contain iron, allow beavers to cut a willow sapling in seconds and chop down a six inch-diameter aspen in a matter of minutes. In Colorado they are most common in areas with abundant willow, aspen or cottonwood, as the bark, buds, leaves and twigs of these plants are their most common foods. The stumps of trees cut down by beavers show their chew marks and are in the shape of an hour glass. At the Willow Spring Open Space, there is an abundance of Sandbar Willow shrubs for them to eat and to use in their dam.
Predators include wolves, coyotes, bear, river otter, lynx, bobcat and mountain lions and humans, who are still trapping beavers.
The Beaver Dam at Willow Spring Open Space
This past winter, beavers started setting up a beaver dam right next to the Englewood Dam. The beaver dam is horseshoe shape and can be best seen from the center top of the Englewood Dam. In prior years, there were beavers further upstream hidden behind the cattails, so not many people knew about them.
I first noticed the start of a beaver dam in December 2020. In this picture, the snow that is remaining on the pond’s ice provides a good outline of the beaver dam and resulting pond. At that time, the dam looked like it was about 2-3 feet tall.
In April, 2021, the beaver dam was more clear, and the cut ends of the willow branches making up the dam could easily be seen.
Their dam is so strongly built that it maintained its shape after being completely covered three times by high waters caused by the heavy rains at the end of June. This dam has altered the Willow Spring Open Space by creating a new pond where there was previously marsh land. This change can be seen by the dead willow shrubs in the pond and the cattails growing into the pond area. The beaver dam looks like it is about 5-6 feet tall as of August, 2021.
Finally Spotted a Busy Beaver!
After many times of trying to spot beavers and seeing only mallards making ripples in the water of the beaver pond, I was delighted to finally see a beaver swimming back and forth bringing Sandbar Willow branches to the site of the dam. When beavers are swimming, generally the only thing you can see are their heads above the water. It was at dusk at the beginning of August, and was a real treat to watch this beaver coming and going for about 15 minutes. I was lucky to see the beaver again a few weeks later – again at dusk.
This evening activity makes sense as beavers are crepuscular (from the Latin word for “twilight”) for animals active primarily at dawn and dusk.
I have not yet spotted their lodge at Willow Spring Open Space. Beaver lodges generally are dome-shaped structures that stick up out of the water and are surrounded by water or built partially up against a bank to safeguard against predators. The typical beaver lodge has an underwater entrance a meter or less below the water surface, which leads to a feeding chamber and an elevated, drier sleeping chamber, which is why they can be seen above the water level. The underwater entrance helps protect them from most predators as the coyotes and bobcats that have been seen in the Open Space do not like to go into the water.
Here is a picture of a mature beaver pond and lodge along the Three-Mile Creek hiking trail on Guanella Pass.
Community news of Beavers at Willow Spring Open Space
About a week ago, when I was looking for their lodge from the top of the dam, a neighbor told me that he had spotted an adult (he was presuming it was the mom) and 2 kits playing in the widened area of the creek below the beaver dam at about 11 pm on a moonlit night. Another friend mentioned that she had seen two beavers at about 6:30 a.m.
What a great connection with nature to be able to observe this wildlife so close at hand!
References and Further Reading
Mammals of Colorado, Second Edition by David M. Armstrong, James P. Fitzgerald and Carron A. Meaney, University Press of Colorado and Denver Museum of Nature and Science, 2011
The Naturalists’s Guide to the Southern Rockies, by Audrey DeLella Benedict, Mountain Press 2008