By John Hadidian
History of a sort was made in October when "beaver deceivers" were installed on European soil—or rather, in water—for the first time.
Pioneered and developed by wildlife biologist and HSUS consultant Skip Lisle, beaver deceivers are economical and long-lasting devices that prevent the planet's second-best engineers from blocking streams and culverts and thereby creating those mini-ponds that can provide refuge and sustenance for beavers—and headaches for humans.
What wildlife managers might call "beaver devices" have been around for perhaps 40 years. In the public's mind, these devices are mostly associated with the Clemson Beaver Pond Leveler, which consists of a pipe, encased in a wire grid, that is used to level out a beaver-made pond by draining water to the other side of the animals' dam.
But in the early 1990s, Lisle, then a biologist working for the Penobscot Indian Nation in Maine, began to work with different design concepts that have come to be called "beaver deceivers" and "levelers." His work has raised the design principles, not to mention the aesthetics, behind beaver devices to new heights, and his devices have proven quite successful when installed at trouble spots throughout the United States.
So when Poland came calling about beaver deceivers, it only made sense that Lisle answered it. Lisle, The HSUS, and Dr. Andrzej Czech, an ecologist and founder of the Polish consulting firm Natural Systems, joined forces to provide the first field demonstrations of this simple but effective technology at two sites near the town of Suprasl in northeastern Poland.
Not long after we helped install Lisle's two different beaver deceivers, the round-fence-and-pipe system and the trapezoidal fence system, the Poles soon learned the great benefits—and the unforeseen complications—of these innovative devices. But more on that later.
Beaver History 101
Before humans almost completely wiped out Europe's indigenous beaver populations for the fur trade, there were dams along virtually every stream in what is now modern Europe. (Incidentally, the European beaver, Castor fiber, is both similar and different from the North American species, Castor canadensis. The two species look alike, but they do not interbreed, and the European beaver has eight more chromosomes in its genetic makeup than its New World counterpart). But that was hundreds of years ago, before the drive to trap beavers for their fur was exported to our continent, with similarly disastrous results.
Today, in both Europe and North America, beavers are making a comeback. Often their return is aided directly by humans translocating the animals, the result of resource managers and ecological planners who have gained an ever-greater understanding and appreciation for the environmental services these animals provide.
Beaver activities create and sustain wetlands; allow sediments and toxic materials to filter out of watersheds before they can harm aquatic ecosystems; and create biodiversity and provide habitat for both plants and animals, some of whom may be threatened or endangered. And that's just a partial list.
Clearly, it is in our interest to have beavers present on the landscape wherever they do not directly affect resources that people need to protect. In fact, some biologists have argued that beaver dams spread throughout a major drainage area—even ones as large as the Mississippi and Missouri basins—will prevent catastrophic floods, since each dam will contribute its small part to stopping, slowing, and impeding the mad rush of water that moves through the channels we have encased in concrete armor.
Even beyond the arguments for humane treatment, the logic for living compatibly with beavers is overwhelming. The trick is to prevent beavers from doing any harm, and for that we can only note that as superb as beavers are as engineers, they are only second-best to humans.
Deceiving Beavers
The term "beaver deceiver" is part of a lexicon that Lisle has created to describe the simple devices he has designed to deter beavers from engaging in what has become modern humanity's principal argument against these animals—the building of dams and the floods they create. Lisle took his knowledge of beaver biology and his experience in construction, and wedded them to create the deceiver concept.
The first thing to understand about beavers is that the urge to dam is deeply ingrained in them. Dam-building is an instinctive survival skill for those mostly aquatic animals; the main purpose of their activity is to surround themselves with a stable body of water that can protect them from predators and provide watery access to food sources in the vicinity.
Centuries of practice have made the beaver an expert on where to construct dams, of course. For the beaver, the stimulus to dam is apparently tied to the sound of rushing water, combined with tactile and visual clues about where is the best site to build their water-blocking devices. These cues typically lead beavers to construct dams where running water is the most vulnerable: narrow areas such as culverts, those man-made, undersized tunnels that channel streams under roadways.
Once a beaver family moves into a neighborhood and discovers a culvert, the results are predictable: flooding, angry residents, and sometimes even impetuous plans to dispose of the pesky animals.
That's where the beaver deceiver comes in. After much trial and error, Lisle determined that by building a fence outward from a road culvert, beavers are forced further and further away from the vulnerable spot in their attempts to dam. The fence—made with cedar or occasionally pressure-treated wood posts and sheets of heavy-gauge steel fencing for durability—literally blocks off a trapezoidal space in the stream, just outside the culvert opening. Beavers cannot penetrate the space from the top, the sides, or even underneath.
The deceivers block access for the beavers, but don't actually plug the culvert; the fencing panels are large enough to allow fish and other aquatic animals through, but not our engineer-oriented wild neighbors. More to the point, these trapezoidal fences push the beaver far enough away from the vulnerable culvert that the animal apparently decides the effort to dam the stream is no longer worth it.
One can almost imagine a beaver stopping along this fence after having laboriously tried to dam the stream, scratching his head, and thinking, "What the heck was I doing here?"
Lisle has found, after much experimentation, that trapezoid-shaped fences tend to be the most effective—they have a narrow front, parallel wings, and a wide back—but beaver deceivers can take almost any form needed to fit to the task and space at hand. Some fences are small, and some are large, perhaps as long as 20 feet or more on the sides.
But sometimes these kind of fences are not used at all, especially when the objective is just to lower the level of water that a dam is holding back. In these instances, a pipe system can be constructed to do the job. The inlet end of the pipe will lie in the beaver-made pond, surrounded by a Lisle-designed "round fence" to prevent the animal from blocking the drain, and the discharge end of the pipe will lie on the other side of the dam. The trick is to create a notch in the dam at the water level you desire.
Beavers may work the site where the notch was made, but once they are committed to repairing and maintaining an established dam they do not typically search downstream for leaks—which is exactly where the pipe system releases the water.
With hundreds of beaver deceivers built and now in place in North America, it has become clear that we have indeed developed a way to maximize the benefits of the beavers while minimizing the conflicts.
Across the Pond to Poland
On the first day of the October 2003 workshop in Suprasl, approximately 40 participants, largely forestry professionals, were on hand to learn about the natural history and ecology of beavers as well as about the humane approaches to resolving conflicts with the animals. Very little management of beavers is presently done in Poland. Dams are either knocked down when they become problematic—which naturally results in beavers dutifully building them back up again—or "nuisance" beavers are shot and killed.
The day after the lectures, a small advance group left to prepare two sites for the installation of beaver deceivers, while the main group stayed back to discuss and decide what its recommendations would be if it were treating these sites.
At the first site, the team installed a pipe-and-round-fence system to level the water at a beaver dam, located away from a culvert at a weaker point in the stream; the dam was beginning to back up water onto the banks of a nearby railroad track. The concern was that the water would weaken the railroad embankment and therefore cause the rails to collapse under the weight of the heavy locomotive.
The team encountered no problems with the installation and promptly moved on to the second site, which was also located along this same railway track. This time around, the team installed both a pipe system and a trapezoidal fence beside a culvert that the beavers had blocked. Perhaps it was overkill, but Lisle figured it was unlikely he would be back to check the site anytime soon, and wanted to ensure that his deceivers would perform their function.
Preparations completed, the team moved back to the first site, met up with the main group as it arrived, and discovered that the pipe was gone. Stolen! Probably not by beavers, either. Industrious as they are, few beaver colonies would possess the equipment needed to move six heavy sections of pipe in a hurry. Rather, it seem humans had been too tempted by the opportunity to help themselves.
Disappointed, but not defeated, the group moved on to the second site, where a complete beaver deceiver system, the first for Europe, was built in falling temperatures and blustery weather. A satisfied Lisle could see that his system was working just fine, thank you. Better yet, he knew the system would require little maintenance, other than an annual drive-by.
Lucky for continental beavers, there will be many more deceivers to follow.
John Hadidian, Ph.D., is director of The HSUS Urban Wildlife Program.
