Barrier Systems For Non Lethal Bird Control

Overhead Wire Systems--Overhead wire systems, consisting of monofilament and stainless steel wire, can be a durable, all-weather alternative to netting for excluding aerial avian predators such as gulls, ospreys, and cormorants from both ponds and raceways. However, when combined with perimeter fencing or netting, a durable, all-weather, cost-effective system can be created to deter herons as well. For example, the Limestone Springs hatchery in Pennsylvania has successfully excluded both great blue herons and black-crowned night herons by using a perimeter chain-link fence to support an overhead monofilament line system spaced at 6-inch intervals. Wire spacing of 10 inches may be adequate. To prevent these birds from landing on the chain-link fence and dropping through the wires, an electric fence was installed along the top of the chain-link fence.

Where a chain-link fence is cost prohibitive, some barrier such as netting at the sides and ends is recommended for preventing both herons and aerial predators from entering to enhance the barrier's effectiveness and to minimize bird injury, streamers or other materials should be hung from lines to make them more visible.

Perimeter Fencing and Netting--Perimeter fencing and netting systems can deter herons and other wading birds from visiting both ponds and raceways. The most effective system evaluated uses two-strand electric fencing. At earthen raceways and ponds the wires are suspended 12 and 16 inches above the water from fenceposts positioned in the water approximately 1 foot from the water's edge. On concrete raceways, fenceposts are positioned in holes drilled in the center of the raceway walls.

The use of nonlethal levels of electric current to shock birds quickly trains them to avoid the area. In some cases, however, herons can learn to avoid the fence by flying directly into the center of the pond or raceway. This happens most often when pond or raceway depth is shallow or raceway flow is low.

Although the cost of this system is low, regular maintenance is required to prevent the electric fence from grounding out. More elaborate nonelectrified perimeter fences and wires also have been shown to provide some protection from heron predation. However, perimeter netting suspended horizontally or diagonally over the water surface is minimally effective. At best, perimeter systems do not deter all herons unless additional protection is provided by an overhead wire system or netting.