Prepared by the National Wildlife Control Training Program. http://WildlifeControlTraining.com Research-based, certified wildlife control training programs to solve human – wildlife conflicts.
Module 6 Exclusion
- Identify common ways that wildlife may enter areas.
- Explain how to determine if an opening is being used by wildlife.
- List commercial products used for excluding wildlife.
- Describe techniques that should be avoided and why.
In the context of wildlife damage management (WDM), exclusion refers to the use of barriers to reduce access of wildlife to resources such as food, cover, and water. This method is both a type of habitat modification and a form of damage prevention. From an IPM perspective, exclusion is one of best and most important methods for dealing with wildlife. It emphasizes prevention, non-lethal control, least invasive, non-toxic, and an environmentally friendly method of wildlife control.
Pros and Cons of Exclusion
Exclusion has many advantages. First, it can be used before any damage occurs. When planting trees in an area with a high deer population, protect newly planted trees with fencing to prevent damage. Second, exclusion does not use chemicals that may harm non-target animals or people. Third, exclusion provides immediate, long-term, and often complete protection.
Unfortunately, exclusion also has several disadvantages. Frequently, clients consider exclusion to be too costly, particularly when large areas need protection (Figure 1). Before clients reject exclusion, advise them to consider the value of exclusion over the long-term.
The second disadvantage with exclusion is the perception that exclusion disrupts the aesthetic beauty of the landscape. Although aesthetic arguments may be over stated, exclusion can often be made less obtrusive. For example, well-maintained wooden fences can add to home values and be attractive. Shrub plantings can be used to conceal fences.
When Considering Exclusion
Know the animal
Different animals require different approaches to exclusion. For instance, does the species burrow, climb, jump, or fly? Can the animal chew through fence materials? Each of these abilities demands a different kind of exclusion.
Whenever exclusion is used, you run the risk of entrapping an animal within the excluded area or building. Never secure openings unless you are certain that animals are not using them. When you are uncertain about whether animals are using an opening, monitor activity by placing dry sticks in front of the opening. If an animal moves through, it will push aside the sticks (Figures 2a to 2b). You can also use crumpled newspaper to plug the hole. Monitor the hole for at least five consecutive days of fair, warm weather. Some animals, such as woodchucks, hibernate during winter in cold climates and will not be active between November and January.
Exclusion for Specific Situations
The type of exclusion to use depends on what is being protected, as well as the type of wildlife you are trying to exclude.
Protecting decks, sheds, and foundation crawl spaces
Structures that lack full foundations (e.g., trailers, sheds, and decks) are vulnerable to entry by skunks, raccoons, woodchucks, and other burrowing animals. Use trench screen to prevent animal access (Figure 3). Increase the depth and skirting of the screen in locations subject to frost heaving or when dealing with wildlife, such as woodchucks, that have a tendency to dig aggressively. Use ½-inch, galvanized mesh wire if more airflow is needed. Pay special attention to corners to ensure that they are properly protected. Screens should overlap 4 to 6 inches to prevent any gaps that could be exploited by digging animals. Crushed gravel is not sufficient for these situations.
Protecting individual trees and plants
Use wire or plastic tree guards to protect trees from trunk girdling. More expensive wire guards provide longer-term damage prevention. When using tree tubes to protect plants, place plastic screen over the top to prevent trapping cavity-nesting birds.
Protect young trees and shrubs from deer damage by installing a wire or plastic mesh fence around the plant (Figure 4). Anchor the fence securely to posts, as animals will bend it to reach branches or the trunk. Fences should be at least 6 feet high to prevent individual plants from deer.
For beavers, place wire fences with 1- x 2-inch mesh wire at least 4 inches away from the trunk. Extend the fence 4 feet high and bury the bottom 6 inches into the soil to prevent a beaver from digging under it.
Use nets to protect trees and other fruit-bearing plants from bird depredation. Ensure that the nets reach the ground, as birds may try to fly or walk underneath. Poles and wires often are needed to support nets for low shrubs such as blueberries or raspberries.
Protecting large areas and gardens from mammals
Fences are the most reliable exclusion technique for preventing damage by mammals to nursery stock, gardens, and home landscapes. Non-electric barriers prevent access to many species and have the added benefit of low maintenance (Figure 5). Electric wires can be added to the outside of non-electric barriers to stop climbing animals such as raccoons and squirrels.
Different animals require different fence designs, so we have provided dimensions and types of fences for excluding common species (Table 1).
Table 1. Types of fences to exclude wildlife
|Species||Fence type||Minimum fence dimensions|
|Deer||Barrier||8 feet high for large areas;
6 feet high for individual plants.
|Deer||Electric||2 strands, 1 foot and 3 feet from the ground for small areas; 7-wire vertical fence for large areas.|
|Rabbits||Barrier||1-inch-mesh wire buried
4 inches into the soil and extending 3 feet above the ground
|Raccoons||Electric enhanced Barrier||1-inch mesh buried 2 inches and extended underground 1 foot. Fence should extend 4 feet above ground with an electrified wire 6 to 8 inches from the top.|
|Raccoons||Electric||2 strands of electric wire 5 and 10 inches above the ground.|
|Woodchucks||Barrier||1-inch-wire mesh buried 2 inches, extending underground 1 foot. Fence should extend 4 feet above ground and have a 1-foot overhang or electric wire 6 to 8 inches below the top to prevent climbing.|
|Woodchucks||Electric||Two strands of electric wire 5 and 10 inches above the ground.|
Unfortunately, fences can be expensive if large areas require protection. Barrier fences typically cost much more than electric fences due to the high cost of woven-wire, posts, anchors, braces, fasteners, and labor. It is common to pay $6 to $8 per linear foot to install wire barrier fences.
Depending on the design, simple electric fences may cost only $1 to $1.50 per linear foot, with most of the cost attributed to the fence charger. Electric fences use a painful but harmless shock to create a psychological barrier to animals. Frequent monitoring and control of vegetation are required to maintain sufficient shocking power (at least 3,000 volts) on the fence. Electricity can be used exclusively, as with the “poly-tape fence” (Figure 6), or in conjunction with a non-electric fence. Fences can be powered through electric outlets, disposable batteries, or rechargeable batteries connected to a solar panel. Modern low-impedance chargers deliver pulses of electricity that deliver a painful, but not continuous, jolt of electricity. The gap in the pulse allows people and animals to move away from the fence. While the shock generally is safe for adults and older children, it could harm young children and people with heart pacemakers. Many chargers can power over 200 miles of fence. Electric fences can be used to protect home gardens from deer and woodchucks during the growing season.
Protecting areas from birds
The mobility of birds makes them difficult to exclude from sensitive areas. Several techniques are available, however, to help reduce conflicts. Use ledge products (either barrier or electric) to prevent birds from roosting or nesting on ledges (Figure 7). These devices are easy to install and make it difficult or uncomfortable for birds to perch at treated locations. Install ledge products on surfaces out of reach of the public.
Nets are useful for preventing bird access to buildings, fruit trees, and gardens (Figure 8). Mesh size of 2 inches will exclude pigeons or larger birds. Use ¾-inch-mesh netting to exclude smaller birds. Select nets that are resistant to ultra-violet rays. Remove nets that are suspended horizontally before winter or secure with them additional support so that they can withstand the additional weight of snow or freezing rain.
Protecting bird feeders
Many gardeners enjoy birds and maintain feeders to encourage birds to visit their yards. Unfortunately, many unwanted animals (e.g., skunks, raccoons, rats, squirrels) may be drawn to the feeder as well. Homeowners should not feed birds during the summer, as birds do not need this food source when natural foods are plentiful.
Many tactics are available for protecting bird feeders. First, place bird feeders on poles 10 feet or more from ledges or tree branches from where squirrels can jump. Install baffles on the pole to prevent animals from climbing. Finally, reduce the amount of spilled seed that can reach the ground by installing catch basins (Figure 9). For detailed instruction, consult “Selective Bird Feeding: Deterring Nuisance Wildlife from Bird Feeders” at http://ianrpubs.unl.edu/epublic/live/ec1783/build/ec1783.pdf.
Protecting window wells
Many people are not aware that wildlife can become trapped in window wells that are 4 inches deep or more. Cover window wells to help prevent this and the potential for a smelly experience when a skunk falls in (Figure 10).
Some cavity-nesting birds (e.g., swallows, wood ducks) and mammals (e.g., tree squirrels, raccoons) view open chimneys as potential nesting sites. They also may gain access to structures through an open damper in the chimney or build a nest on a closed damper, resulting in a fire. Cap all chimneys with approved commercial covers (Figure 11).
This module highlighted only a sample of the products available to exclude wildlife. We encourage readers to obtain product catalogs from wildlife control supply companies. Members of trade association such as the National Wildlife Control Operators Association are always testing new products and are a good source of information. If you are interested in this topic, we suggest that you enroll in the professional National Wildlife Control Training Program.
Questions for Reflection
- Define exclusion and provide two examples.
- A client says she is in a hurry and just wants a hole closed. How would you respond?
- A client complains that the cost of exclusion is too high. How would you respond?
- What options are available for excluding birds?
- Describe how you would prevent skunks from accessing the space under a deck.