Nuisance Wildlife Pests

Increasing urban development of agricultural and wooded areas has forced many species of animal wildlife from their native habitats. The best control efforts involve a gentle push, not a swift kick.

My wife and I have lived in the suburbs for the last 25 years, but not until we moved to suburban Maryland 10 years ago, did I realize the impact that humans have on native animals which often are considered to be pests. From their perspective, humans are the true pests encroaching on their natural environments.

Over the years in our own backyard, we have observed deer, field mice, grey and red fox, racoons, woodchucks, chipmunks, squirrels, rabbits, opossum, skunk, turkey vultures, bats, pheasants, geese and various other birds. Many of these animals have exploited areas near or in our house as nesting sites, such as in the garage, basement, under the flagstone patio, between the rock-lined steps, under the front porch, and in the woodpile.

Our housing development is typical of those in our area and in many locations throughout the United States where developers are building on agricultural lands and the wooded areas abutting them, thus depriving native wildlife of their natural harborage sites and food resources. As animals seek out harborage and food in their newly modified habitats, they discover that creeks and streams have been converted to culverts and underground drainage systems; that most, if not all, trees have been replaced by man-made structures, e.g. houses, light poles, etc.; and that their food supplies are greatly diminished.

It is easy to see how raccoons may perceive a chimney to be a hollow tree, how bats and squirrels may see an attic as a warm place in which to nest and over-winter, and how chipmunks and field mice find rock walls and woodpiles to be attractive nesting sites.

THE THREAT OF DISEASE. The most important result of human encroachment into wildlife habitat is the increased risk of exposure to zoonotic diseases such as histoplasmosis, Lyme disease, hantavirus and rabies. Histoplasmosis is the most subtle of these diseases. It often goes undiagnosed because of its flu-like symptoms, e.g. fever, dizziness, headache and respiratory illness. It is caused by the fungus Histoplasma capsulatum. This organism typically grows in soil that has been enriched with bat or bird droppings. Spores are produced which can become airborne if the soil is disturbed. Inhalation of these spores may cause infection. Pest control specialists are at risk when working without proper respiratory protection in poorly ventilated spaces where bird or bat droppings have accumulated, such as attics.

Lyme disease is the most widespread zoonotic disease in the United States that is associated with deer, field mice, and black-legged ticks. It is diagnosed in more than 10,000 individuals annually. Its effects include a bulls-eye-type rash around the site of the tick bite, joint pain, and, in advanced states, arthritis and cardiac involvement.

Hantavirus, which is the most recently diagnosed zoonotic disease in the country, is also associated with field mice and is contracted by inhaling particulate matter that has been contaminated by field mouse urine and droppings. The advanced states of hantavirus result in respiratory problems and death in approximately 60% of diagnosed cases.

Rabies exposure occurs through the introduction of contaminated saliva into an opening in the skin or from the bite of an infected animal. Animals typically affected by rabies include fox, skunk, raccoons, bats and woodchucks. Early treatment of the disease typically results in full recovery, but, except in extremely rare cases, failure to treat results in death. Severe bites are likely to occur when wild animals are approached, fed and handled.

A HIGH POTENTIAL FOR DAMAGE. Damage to structures by wildlife can be extensive and expensive to repair. Most damage is related to the process by which animals gain entrance to the structure, the creation of nesting sites, and to the filth generated by their droppings. Significant damage can also occur when animals are trapped or harassed by humans.

A recent incident occurred in a nearby suburban area in which children came upon several deer in their backyard and began to chase them through the neighborhood. The terrified deer, in their attempt to escape the children, jumped through plate-glass windows in neighboring houses, resulting in thousands of dollars in damage to furniture, walls and other property within the homes as well as to themselves as they became injured. At least one deer had to be destroyed. Fortunately, no humans were physically injured, although they easily might have been.

Several years ago, a pest control company was called in order to trap squirrels that were nesting within the attic of a house, and to prevent them from re-entering the house. The job took place during the homeowner’s vacation. Unfortunately, the company failed to ensure that all the squirrels were out of the attic before the exterior entryways were sealed. The squirrels wreaked havoc in their attempts to exit the attic, eventually chewing their way through the ceiling into the living spaces of the house and tearing up upholstered furniture and other property in their search for food and escape.

Consumers most often complain about wildlife damage to ornamental plants, shrubs and trees. Damage can result from wildlife animals’ eating buds and foliage and rubbing bark off of young trees. Both of these situations may result, at worst, in the death of the vegetation, and at best, in disfigurement of the plants as well as in ticked-off homeowners who may, in turn, seek revenge on the wildlife in question.

THE BEST CONTROL EFFORTS. Wildlife problems are best controlled through preventative efforts. Wildlife should not be intentionally fed and encouraged to enter the yard. Pet food should be stored indoors in tightly sealed metal and heavy plastic containers. Garbage cans should be of similar construction. Fences and netting offer limited protection. Plants and inanimate objects (e.g. plastic garbage cans, door seals, etc. can be treated with repellant materials to discourage feeding and gnawing activities but these repellants must be reapplied after they become wet. Exterior areas should be inspected for openings (e.g. doors, windows, siding, pipe wire penetrations soffits, roof lines, etc.) larger than ¼ to ½ inch in width and diameter. Such holes should be permanently sealed using ¼-inch hardware cloth, sheet metal, copper gauze, cement and similar materials.

Tree branches, ivy and other climbing plants which are in contact with the structure should be cut back. Above-ground wires leading to the structure can be protected by placing a plastic golf club sleeve that has been split in half lengthwise over them.

Trapping, which is difficult because wild animals are very wary of changes in their environment, should be used with care only as a last resort and to remove animals that have gained access to a structure. The disposal (i.e. relocation and euthanasia) of a trapped animal should be coordinated with local fish and wildlife authorities.

When dealing with raccoons, for example, live-trapping with cage-type traps is probably the best method of trapping for the novice. Live-catch box-type traps constructed of wood, sheet-metal or wire mesh probably offer the best method of removing skunks from beneath or around buildings. Traps should be secured to a tree, fencepost, or stake-driven alongside the trap to prevent the animal from tipping it over and stealing the bait without entering the trap.

Toxicants, such as zinc phosphide, fumigants, smoke bombs and anticoagulants, should be used only as a last resort to control wildlife. These types of products can endanger or kill nontarget animals and wildlife. Use of these products should be coordinated with local fish and wildlife authorities.

As natural animal habitats continue to decline as a result of development, increased problems can be expected to occur. In light of this, it’s easy to understand why, if we could talk to the animals, they would tell us that we, not them, are the true pests.

Richard Kramer is contributing technical editor for PCT.

Sidebar: BIOLOGY OF COMMON VERTEBRATE PESTS

Chipmunks: Chipmunks are among the smallest members of the squirrel family (Sciuridae). They are found in most of the 48 contiguous states but are limited in some of the Great Plains states and rare or absent in Texas and Florida. They are common in the Northeast, from Canada westward to Michigan, and in the Rocky and Sierra Nevada mountains.

Chipmunks are basically ground-dwellers but often climb trees and other objects for food and protection. Where chipmunks are found around residences, it is not uncommon to find them sitting or running on porch railings, fences and rooftops. All species of chipmunks breed during spring and summer. Following a gestation period of about 29 to 31 days, litters of two to seven young are produced.

Deer Mice: There are several species of "deer mice," but all of them belong to the genus Peromyscus and are collectively referred to as white-footed mice. Every part of the country has one or more species of deer mice. Slightly larger than the introduced house mouse, deer mice are easily distinguished by their relatively large eyes and ears. The tail is covered with short, fine hair and is distinctly bi-colored, dark on the top and white on the bottom. Its feet and underbelly are also pure white.

Deer mice have three to six young per litter and three to four litters per year, although figures vary with climate. The gestation period is 21 to 24 days with the main surge of reproduction occurring in the spring. Nocturnal animals, deer mice feed primarily on seeds. In the wild they are numerous and occupy a wide variety of habitats, but despite their numbers, are seldom seen. They nest in hollow stumps, beneath fallen logs or in small shallow burrows.

Raccoons: The raccoon, Procyon lotor, is one of the best known of all the furbearers. It is a huskily built animal: the average raccoon weighs 10 to 16 pounds, although an occasional adult male may reach 50 pounds. It is found throughout the U.S.

The raccoon is omnivorous, feeding upon fish, frogs, small mammals, birds and their eggs, mollusks, crustaceans, fruits, nuts, small grains in storage and in fields, and certain vegetables such as corn. Tracks in the mud or dust which look like small human hand prints often reveal that raccoons may be quite common in an area even though only occasionally seen because they are noctural and seldom move about during daylight.

Raccoons are often found near a marsh, stream, lake or pond, but many venture away from natural water. They prefer trees or brush as natural cover. They do not dig dens of their own, preferring hollow logs, hollows in trees and other natural shelters. The single litter per year, in the spring, varies from two to eight young, and the gestation period is 63 days.

Deer: Deer, which are even-toed ungulates of the family Cervidae, are probably the most widely distributed and best-recognized large mammals in North America. Adult animals may weigh 50 to 400 pounds depending on size and location.

Deer are creatures of the forest edge rather than of the dense, old-growth forest. They thrive in agricultural areas interspersed with woodlots and habitats near waters. Staple foods include leaves, stems, buds of woody plants and, seasonally, fruits and nuts (especially acorns) are very important. Agricultural crops are also readily eaten when available.

Most active in early morning and evening, deer have a home range of several hundred acres, but this varies with season, gender and habitat quality. Breeding occurs from October to January depending on latitude. Gestation is about 202 days.

Sources: The Mallis Handbook of Pest Control, 8th Edition; Prevention and Control of Wildlife Damage.