by Blair Hurst, Walsh Environmental


Those deer ate my flowers! That bear rummaged through my trash! That beaver plugged my culvert! These and other similar experiences remind us that while we may have successfully established communities, homes and gardens, we continue to share the landscape with our resident wildlife. One noted and oftentimes-unappreciated member of the wildlife community with whom we share riparian, wetland and stream areas is the industrious American beaver.
Scientifically known as Castor canadensis, the American beaver is indigenous to the North American continent while the European beaver, Castor fiber, is its not-too-distant cousin. Historically occurring in most areas with flowing or standing freshwater, the unregulated capture of beaver for their pelts, musk glands and tails in North America during the 1800’s led to their near extinction. Protection and relocation efforts have helped to re-establish local populations. However, it is estimated that restoration of only approximately 10 percent of the historic beaver population has been achieved in the West.
Commonly known as nature’s ecosystem engineers, beaver are considered a “keystone” species in that they modify their natural environment in such a way that the overall ecosystem builds upon the change. Second only to humans in their ability to manipulate their environment, it is estimated that up to 85 percent of wildlife in the West at some point in their lives depend upon the habitats that the beaver creates.
The engineering efforts of the beaver greatly modify ecosystem process and influence biota. Benefits associated with beaver activity include, but are not limited to, the creation of wetland areas, groundwater recharge and water table elevation, increased willow production and vegetative cover for riparian wildlife, creation of pools and cool water habitat for fish, reduction in water velocity and channel shear stress, and suspended sediment removal from the water column.
While their industrious building and creation of ponds benefits a large number of wildlife species, beaver are not necessarily mindful of sharing their environment with humans! Driven by the sensory cue provided by the sound of flowing water, beavers preferentially build dams in areas of water constriction and increased velocity. In developed land settings, these areas frequently coincide with culverts and bridges for road and railway crossings. Beaver-felled trees and limbs plug culverts and catch on bridge piers, raising the water surface elevation, threatening the crossing, and, unfortunately, casting the beaver as a nuisance.
As proponents of Colorado’s riparian, stream and wetland areas, we all understand the values of, and need for, both healthy ecosystems and sound infrastructure. Achieving these objectives simultaneously is ultimately an issue of balance and creative solutions. Fortunately, two individuals, Sherri Tippie and Skip Lisle, stand out as leaders in the quest to successfully coexist with the beaver over the long-term.
Denver resident Sherri Tippie is Colorado’s renowned lover and sole licensed live trapper of beaver, trapping and relocating anywhere from 30 to 50 beavers annually. Specializing in beaver education and relocation through her non-profit organization Wildlife 2000, “Tippie”, as she is affectionately known in certain circles, is one of the few resources for anyone seeking economically-viable, environmentally-friendly, and mutually beneficial alternatives to killing dam-building, tree felling beaver. Frustrated landowners or floodplain administrators have called upon Tippie to trap beaver in metro Denver’s urban streams and release them in rural areas where their labor is appreciated for creating wetlands, raising water tables, storing surface water, restoring top soil, and slowing water velocities. “Nuisance” beavers are welcomed with open arms by many, including ranchers hoping to raise the water table for subsurface irrigation of forage for sheep, cattle, deer and elk, fishing clubs looking to create and improve fish habitat, and owners of creekside property who would like to stimulate vegetation growth and prevent soil erosion. For more information about Wildlife 2000, or to volunteer or donate to beaver trapping and relocation efforts, contact Sherri Tippie at             303.935.4995       or

The Castor Master

Vermont wildlife biologist Skip Lisle has been experimenting with fences and flow devices aimed at beaver-proofing culverts and stream channels where flooding could be an issue. Lisle’s “beaver deceiver” and “castor master”, with customized site-specific designs, have worked with great success in several settings. A typical beaver deceiver, shown in the figure to the right, is used at culverts. It is a trapezoidal structure made with cedar posts and heavy gauge wire fencing that is narrow at the culvert and widens upstream. The trapezoidal fences push beaver far enough away from the vulnerable culvert that the animal apparently decides that the effort to dam the stream is no longer worth it.
The castor master is a simple flow device used to set and maintain the maximum water surface elevation backed up behind a beaver dam. It consists of a caged filter atop an upright drain that feeds a pipe running through the beaver dam. The upright drain is set at the maximum water surface elevation the property owner determines for the pond. When the pond reaches this maximum height, water flows into the drain and through the pipe. This reduces the pond’s water level and the potential for flooding adjacent land and structures. Since the beavers are unable to plug the caged filter, the desired maximum water level is never exceeded and the presence of beaver can be at least tolerated, if not appreciated and enjoyed.
A castor master has been in place and functioning properly for over three years at the Telluride Golf Club, where beavers have rebuilt their dams and ponds around the structure since its installation. Here, the beaver are maintaining a healthy wetland ecosystem, where bird species, deer, elk and other wildlife take advantage of the habitat. In this case, an investment of $250 and 20 hours required to install the device saves 10 hours of labor per week, as workers no longer remove debris and clean up behind the beaver. The site serves as an example of a sensitive solution for dealing with growing beaver populations in the area, and has been used for demonstrations on the functioning of the castor master and as an educational opportunity for school groups to learn about beaver ecosystems. For further information regarding these flow devices, contact Skip Lisle at             802.843.1017      ,, or visit
As an example of their current efforts educating the public and working with beaver, both Sherri Tippie and Skip Lisle spoke and provided training at a workshop sponsored jointly by the New Mexico Environment Department and Animal Protection of New Mexico. The free workshop, Coexisting with Beavers by Preventing Damage, was held May 20th and 21st in Santa Fe. Day one of the workshop was open to government agency participants only, and day two of the workshop was open to the public. For further information, visit
With proper planning and consideration of their habitat needs, the large majority of beaver-human conflicts may be prevented or solved at a surprisingly small cost. This will eliminate the need to relocate or kill beaver each time they reoccupy available habitat. This approach also helps to maintain the integrity of aquatic and riparian habitats and, perhaps most importantly, serves as an example of how we can successfully share the landscape while deriving unexpected benefits, such as more clean water and greater species diversity, provided at no expense by our original North American ecosystem engineer.

Colorado Riparian Association