November 7, 2019 at 3:47 pm
By Regional Wildlife Biologist Chuck Hulsey
Beaver are valuable semi-aquatic furbearer whose presence enhances wetland function as well as benefiting many species of fish, insects, reptiles, amphibians, birds, and mammals. But their need to impound water can also impact road culverts. This is especially true in cases where the road inadvertently functions as a dam, and the culvert is viewed by beaver as a leak needing to be fixed. So on September 25th and October 3rd training was held in Wilton and Buckfield to teach beaver ecology, and to share proven methods to exclude beaver from road culverts.
The training was for folks who manage and maintain our roads and highways or are responsible for resolving these types of human/wildlife conflicts. It was planned and conducted jointly by Ben Nugent, Wildlife Biologist, USDA-Wildlife Services, Scott Lindsay, Regional Wildlife Biologist, Maine Department of Inland Fisheries and Wildlife in Gray, and Chuck Hulsey, Regional Wildlife Biologist, MDIFW in Strong.
We started with a brief classroom session to share information about beaver biology and behavior, and to introduce various methods to exclude them from culverts. Then most of the training involved a hands-on exercise which was the construction of an exclosure and water-leveler at a chronic problem site. Approximately 50 people combined attended the two sessions. They included biologists from MDIFW, USDA-Wildlife Services, Maine Department of Transportation, municipal highway departments, a large forest land manager, and private Animal Damage Control agents.
In Wilton, the class built a standard arc-shaped fence in front of a Town of Wilton culvert on Bennet Road. Salvage channel posts (from road signs) were driven into the stream bottom, about two feet apart, in a half-circle, 4-6 feet in front of and to the sides of the culvert. Heavy-gauge livestock fence panels were affixed on the upstream side of the fence. The bottom 18 inches folded 90 degrees and that part set flat on the stream bottom to deny access from underwater. The length of the fence is 4-5 times the diameter of the culvert. The purpose of the fence is to prevent beaver from building their dam inside or blocking the front of the culvert. If they do build or re-build, we want the dam where we want it, which well out in front of the culvert. This keeps the culvert flowing.
A water leveling device is sometimes needed if a new dam on the fence would raise the water to a point where it could be a problem. In this case, we did not want the water to rise to where it could flow onto a nearby recreational trail. So, the class utilized a 15” by 20-foot plastic culvert as a leveler. The upstream end was blocked with a heavy-duty livestock dish and a long slot cut on the underside where the water could enter. That was wrapped with chain link fencing to prevent beaver from blocking it with debris. The downstream end passes through the fence at an elevation that allows beaver to have enough water to survive but not high enough to be a problem. The leveler serves as a leak in the dam that beavers hopefully cannot fix. The secret to success is keeping both the beaver and human satisfied.
The Buckfield class built a slightly different structure on Rt. 117 about one mile west of the village center. The exclosure for that culvert was constructed on land. It has a floor and a top for rigidity because lighter duty “T” fenceposts were used for support and placement. This type of fence post is economically priced, readily available, and easier to drive in by hand with a light-duty fence post pounder. Again, heavy-gauge livestock panel fence was used. The floor also helps prevent beaver from getting to the culvert from under the exclosure.
A water leveler was also needed at this site to keep water off the abutting landowner’s field. In this case, the class constructed another exclosure to receive the upstream end of an 18” by 20-foot plastic culvert. With this design, the water intake is under the surface, near the bottom. The downstream end passes through the culvert exclosure. As with the Wilton structure, that elevation is set to leave the beaver enough water to survive, but not enough to flow onto the neighbor’s field. These devices are most successful when two things are achieved. First is denying beaver access to the culvert. Second is to meet the beaver’s need to have some impounded water so they will accept the presence of the structure. Acceptance of the structure is greatly enhanced if installed proactively before a problem re-occurs.
We use the livestock panels because they are heavy gauge wire which will last a long time and reasonably priced. As important, the 6” by 6” pattern allows fish and small wildlife to pass. In Buckfield we modified the structure very slightly to allow turtles and other wildlife larger than 6” to escape if they entered the exclosure from downstream. See the photo below.
We wanted to provide this training because modifying a problem site using exclosures is usually less costly and more effective than removing the problem beaver. Why is that?
Because every year beavers age one to two will leave their home colony to look for unoccupied habitat. This annual dispersal almost guarantees another plugged culvert if there is food present (deciduous trees and shrubs) and void of other beaver. So exclosures address the beaver of the moment as well as all future beaver. In the words of former MDIFW Wildlife Technician Jim Dorso, who was the first to use this technique in Maine, “You will be ahead of the game if you view a plugged culvert as a water problem and not a beaver problem”.
Images by Chuck Hulsey