Locating and Managing Peninsulas for Nesting Ducks
Construction Guidelines for Predator Barriers
Electric Fences
Most electric fences used as predator barriers consist of a wire mesh fortified with electric wires to prevent predators from moving over, under, or through the fence. Electric fences have been constructed in three basic configurations depending mainly on the shape and location of the peninsula (Figure 2). On peninsulas with narrow isthmuses, the fence is built straight across the isthmus. On peninsulas that terminate near the far shore (closer than 200 feet), one fence is built straight across the isthmus and another fence is built straight across the tip. On peninsulas with broad isthmuses the fence must extend in two directions from a corner.
| Figure 2. The three styles of electric fences showing a pointed peninsula with a single fence barrier, a pointed peninsula with two fence barriers, and a blunt peninsula with a fence that extends in two directions. |
The ends of all electric fences should extend about 50 feet into open water to a depth of at least 1 foot (0.305 m) based on average wetland levels. If electric fences have to project 100 feet or more into the wetland to reach a water depth of at least 1 foot, the peninsula probably cannot be managed cost-effectively.
Most electric fences have a permanent dry land portion and an attached but removable wetland segment (Figure 3). Wire mesh on dry land portions of electric fences should extend from 1 foot below ground to 5.5 feet above ground. In wetlands, the wire mesh should extend from the pond bottom to 5.5 feet above the bottom. The dry land portion of an electric fence normally includes two kinds of wire mesh. The upper mesh should be a galvanized wire such as poultry netting (1-inch or 2.54-cm mesh, 18-gauge), welded-wire fabric (1 × 2-inch mesh, 18-gauge), or horse-fence (2 × 2-inch mesh, 16 gauge). The upper mesh serves as a ground for the energized wires so it must be connected to an earth ground. Vinyl-clad wire mesh is often used for the lower 2 feet, including that below ground, to prevent rusting. The 2 wire meshes are woven together with stainless steel wire or fastened together with hog-rings.
| Figure 3. Detailed illustration of the standard electric peninsula fence showing the dry land portion, the wetland portion, and the electrical connections to the solar-powered energizer. Measurements are in inches. |
The top 1 foot of electric fences should lean towards the base of the peninsula at a 45° angle. If coyotes are not present in the region, a overhang may not be needed and a fence height of 4.5 to 5 feet would be sufficient. If there is a threat of fire, vegetation 5-10 feet on either side of the fences should be mowed to prevent flames from scorching the wires. Scorched wires will soon rust and deteriorate.
Three energized wires (12.5 gauge) are attached to the side of the electric fences facing the base of the peninsula. Two energized wires are placed 4 feet above ground and 2.5 inches and 5 inches from the wire mesh. The wires are held in place by fiberglass rods that are driven into the wooden posts and by insulators that are nailed to the wooden posts or attached by spring clips to the wire mesh. The third energized wire is placed 2.5 inches above the top of the wire mesh. This top wire is connected to insulators that are attached to the rod that supports the 45° overhang. All wire mesh and electrified wires must be stretched tightly.
A small, high-voltage energizer, powered by a 12 volt deep-cycle marine battery, is used to electrify the wires. The battery charge is readily maintained through the use of a solar charger.
To reduce water and ice damage to segments of the electric fences in the wetland, use commercially available "cattle panels" (16 × 4.25-feet, 4 gauge). Each panel should be covered with 1-inch wire mesh, and an energized wire placed near the top. The energized wire is attached to the wire mesh on each panel by a spring clip insulator. The panels can be fastened together with hog-rings or stainless steel wire and held upright with fence posts that are driven into the wetland bottom. The panels should be placed in the wetland each spring after the ice melts and removed after the nesting season before the lake freezes.
Fences should be checked regularly for electrical malfunctions and structural damage. Materials for electric fences are available at lumber companies, farm supply stores, and from national distributors (Appendix A). Additional details concerning electric fence construction and operation is found in a manual prepared by Rondeau and Piehl (1989).
Water-filled Moats
Water-filled moats can also be used as effective predator barriers to reduce access of certain mammalian species to peninsulas. Moats should have 3:1 side slopes with a water barrier that is 200 feet or more wide and at least 3 feet deep, based on average wetland levels. Moats are expensive to build and, therefore, best suited to peninsulas with narrow isthmuses. Earth removed from the excavations can sometimes be used to increase the peninsula area or to create nesting islands.
| Water-filled moats also provide effective predator barriers. In many cases the excavated soils can be used to extend the peninsula. (photo by Harold Umber, North Dakota Game and Fish Department) |
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