In a perfect world, humans and wildlife would coexist without much interaction. However, as humans continue to convert wildlife habitat into human habitat, problems inevitably occur. While many people enjoy the presence of wildlife, under specific conditions certain animals have the potential to threaten other wildlife populations, the environment in which they live, agriculture and aquaculture industries, and human health and safety.

A previous Lake and Watershed News article (“Fowl Play: Nuisance Waterfowl and Lake Water Quality,” September 2003) addressed the issue of nuisance waterfowl, but other wildlife species can be detrimental to aquatic ecosystems in certain circumstances. Beavers, muskrats, and nutria are all aquatic mammals in the rodent family that have a tendency to modify lake and wetland habitat. Most of the damage caused by beavers is the result of bank burrowing, dam building, tree cutting, or flooding. Beavers cut trees along the water’s edge to build their dams and lodges; this can damage riparian buffers and creates a nuisance to shoreline homeowners who value their trees. In addition, beaver dams can block creeks, drainage ditches, culverts and spillways, causing adjacent lands and roads to be damaged by flooding and erosion.

Beavers, muskrat, and nutria can weaken levees or earthen dams by burrowing into the banks, which may cause them to collapse during periods of high water. The holes made for their burrows along the shoreline can represent erosion problems. In addition, large populations of muskrats and nutria can eat excessive amounts of aquatic vegetation, making the habitat less suitable for other wildlife.

If loss of trees is the main problem, trees can be fenced using heavy-gauge fencing with a mesh opening of no more than 2-inch x 4-inch around the base of the tree, six inches away from the trunk and extending to a height of four feet. In situations where beaver dams are blocking culverts and threatening roads, a strong woven wire fence can be staked 10 to 15 feet in front of the culvert, which physically prevents the beavers from accessing and plugging the culvert. In certain situations where beaver dams have altered water flows, a water level control device (WLCD) may be effective in reducing flooding to a tolerable level for landowners. A WLCD minimizes the sound and motion of running water so that it’s less noticeable to the beavers. Ideally, beavers can continue their activities but should not be able to plug the device. Sometimes, breaching of beaver dams is necessary as an interim measure to relieve flooding until the beavers are harvested during the trapping season, or while exclusion structures are installed. This is not an effective long-term control option, however, because the beavers will rebuild the dam each night.

For muskrats and nutria, barriers to prevent burrowing offer the most practical management solutions. A properly constructed filter layer such as rip-rap will discourage burrowing into human-made water control structures, as will heavy wire fencing laid flat against the slope and extending above and below the water line. Another option is to dig a trench extending lengthwise of the fill about three feet below water level, and fill the trench to one foot above water level with concrete. If burrows causing erosion damage to natural streambanks is the primary concern, backfilling, or “mud-packing,” the burrows may be an option. If nuisance aquatic rodent activity is severe, hunting or trapping may be an option. Hunting and trapping activities are regulated in most states as are modifications to culverts and dams, so contact your area Fish and Game Commission or DEP for more information.

As most people are aware, white-tailed deer populations have exploded in the US as humans have converted more and more deer habitat to developed land. For example, before the turn of the last century,  Pennsylvania had an estimated 8 to 10 white-tailed deer per square mile. Today it is estimated that there are approximately 30 deer per square mile in Pennsylvania , or 1.5 million deer. Deer population control in suburban areas has become a somewhat controversial subject. Many people enjoy seeing the animals and oppose hunting and other lethal efforts at controlling the population. Others are continually frustrated by deer eating their gardens and posing driving risks. Large populations of deer can over-browse riparian buffers, therefore reducing the effectiveness of the buffers. Deer prefer to feed on new forest growth, causing forests to revert to single-aged stands with only a few species able to survive the deer’s winter feeding frenzy. Over the long term, this can lead to depletion of understory plants and wildflowers, as well as the birds and other animals that feed on them or require them for shelter. Very excessive numbers of deer can erode streambanks with deer trails and crossings, and contribute nutrients to streams via their feces.

There is no one easy solution to the problem of deer overpopulation, and the first step in developing a management plan should be to assess the current status of the deer population via monitoring studies or infrared surveys. The next step in deer management is a public education campaign, and a restrictive ordinance prohibiting deer feeding. Encouraging hunting in overpopulated areas, especially antlerless deer hunting, is one of the more effective ways to manage deer overpopulation. Besides hunting, which may not be an option in more population-dense areas, trained sharp-shooters or controlled archery organizations can be hired under special permit to cull the deer population in defined areas. These experienced hunters can reduce localized populations in a short period of time, often at night when their activities would be less disturbing to local residents. 

The deer meat is often donated to local food pantries. If lethal deer control methods are not applicable or preferred, several non-lethal deer control methods exist. Fencing and repellants (via odor or taste, such as bonemeal) can be effective techniques for site-specific deer damage problems; however, these methods will not decrease damage on a watershed scale. In residential areas, damage can sometimes be reduced by planting yard vegetation that is unpalatable to deer. However, when deer densities are high or natural foods are limited, deer may browse on species they would not otherwise eat. Visual or audio deer deterrents are commercially available, as are special highway warning reflectors to discourage deer from entering roadways in front of cars at night. The chosen deer control method(s) should be based on public input and the site considerations of the specific watershed.

It is important to keep in mind that although aquatic rodents and deer can be problematic when their numbers are excessive, moderate populations of these animals can be critical to natural ecosystems. Deer browse has evolutionarily kept certain native species of plants in check while allowing others to flourish. Some researchers believe that beavers may be keystone species in certain ecosystems since they create and maintain shallow marsh habitat that other species require for survival. When natural ecosystems are preserved, wildlife species have plenty of habitat without encroaching on human land uses.

For more information on nuisance wildlife control, invasive species, and other lake and watershed issues, keep your eye out for the upcoming Pennsylvania Lake Management Society (PALMS) Pennsylvania Lake Management Handbook at http://www.palakes.org.

Next newsletter: Hydroseeding: The Most Bang for your Buck.