EVALUATION OF THE EFFICACY OF VARIOUS DEER EXCLUSION DEVICES AND DETERRENT TECHNIQUES FOR USE AT AIRPORTS

Thursday, October 21, 2010

Selection of effective techniques by airport managers for deer control requires a “zero tolerance” approach. No single method provides 100% effectiveness, or is appropriate at all times. Deer populations are dynamic and they adapt readily to many methods to manage or control them. Exclusion with a tall perimeter fence and removal of deer that manage to penetrate the fence is the most effective means of minimizing deer interference within airport operating areas. Fences must be designed to counter the ability of deer to crawl through or under fence gaps as small as 23 cm and to jump over 3-m high fences. Fences must be at least 3.7 m tall in order to provide an effective barrier.

At smaller airports, costs may limit the use of tall chain-link security perimeter fences. A less expensive, but equally effective fence is a made with high-tensile fixed knot galvanized steel mesh. These high-tensile fences offer an approximate saving of 30 to 40% of the cost of chain-link fences with equal effectiveness. Tall high-tensile electric fences are available at lower cost than high-tensile fixed knot fence, but with lower exclusion performance and higher maintenance requirements. Tall polypropylene deer fencing has potential to provide effective exclusion, but use at airports has not yet been tested.

Cattle guards should be used at points of vehicle entry through fences that must be left open for periods of time. Harassment-based deterrents are recommended for short-term control of deer that penetrate perimeter fences until more permanent removal techniques can be used. Longer-term use of harassment is not recommended because of habituation by deer. One-way gates and deer jump ramps can be effective means for allowing deer to go back through the airport perimeter fence. Habitat modification should be used to enhance the function of the perimeter fence by reducing the attractiveness of the airport property to deer and to eliminate gaps under fences to inhibit deer from crawling under the fence and to offer a path for deer to allow them to run along the fence to discourage jumping.

Chemical immobilization and killing of deer are the most humane methods of deer removal, but negative social response often prevents the use of these methods at airports near urban centres. Active deer capture and relocation of deer using deer traps and drive nets requires a large number of skilled personnel and is generally not recommended due to high mortality of relocated deer, high costs and a lack of suitable relocation sites.

Methods of harassment such as gunshots, pyrotechnics, gas cannons, and flashing lights may provide some initial response, but deer will often habituate to these devices within a week. Chemical odour and taste repellents are generally ineffective and are impractical for use on areas as large as airports.

We sorted the deer exclusion devices and deterrent techniques reviewed in this report into three broad categories: (1) Highly Recommended, (2) Limited Recommendation, and (3) Not Recommended.

a. Highly Recommended

Five products/techniques are highly recommended. Habitat Modification should be used to reduce attractiveness of airports to deer and enhance the effectiveness of perimeter deer fencing. Galvanized Steel Chain-Link Fencing of a height of 3 m or more is the current standard type of fencing for security and deer control. Its high initial cost is the main reason that its use is generally limited to large airports. High-Tensile Fixed-Knot Fencing of a height of 3 m or more is an effective deer control at a saving of approximately 30% of chain-link fencing. Cattle Gates longer than 4.6 m are an effective means of deterring deer from entering at fence openings that must remain open for vehicle passage. The sides of the cattle gate should be fenced to improve their effectiveness. One-way Gates, located at the outside corners of airport perimeter fences are an effective means of removing deer that have entered a perimeter fence.

b. Limited Recommendation

The majority of the deer control products/techniques reviewed here fall into the limited recommendation category. They can exclude or deter deer but they are limited in their effectiveness because of habituation, weak biological basis, limited application, and/or implementation problems. These products work best when part of an integrated program, and should not be considered individually as key components of a control program. They may, in some circumstances, be useful tools to have in your animal control “toolbox”.

Eleven products/techniques have been given limited recommendation. Electric fences such as the Vertical High-Tensile Electric Fence and ElectroBraidT Electric Fences that have sufficient height to prevent deer from jumping are effective in excluding deer under favourable conditions, but they will be penetrated when deer are motivated to cross them, when short-circuited by tall plant growth, or if snow accumulations exceed the height of the lower electric lines. Plastic Mesh Deer Control Fencing is currently marketed for residential deer control and may promise to be effective for airports, but no independent testing of this fence is known for areas as large as airports. Deer Jump Ramps promise to be effective means of permitting deer that have penetrated a perimeter fence to make their way back outside of the fence, but very little literature was available to confirm this. Chemical Immobilization to assist in live removal, or for facilitating euthanasia, is an effective deer-removal method for deer that will not leave via passive means, but dangers to staff and costs involved, availability of trained personnel and effort of relocation may make this method of control undesirable. Live Deer Traps and Drive-netting are high effort, high-cost deer removal methods that require large numbers of trained people and risks of erratic movement of chased deer within airport operations areas may compromise airport safety. Controlled Hunting may be an effective means of controlling the local deer population in rural areas that may permit it, but it should be used to reduce numbers outside of the airport property at sufficient distance so as to not reduce airport safety. Infrared Motion-Sensing Equipment is a high-cost detection system that is in the development stage. Currently it shows promise for airports with an existing wildlife control staff available to respond to wildlife “occurrences”. Further development is needed to bring a cost-effective product to market. Pyrotechnics, Gas Cannons and “Exploders” can offer effective short-term control and should be replaced by more permanent methods when habituation develops.

c. Not Recommended

Fourteen products/techniques are not recommended. Electric fences such as the Livestock Outrigger Fence, the Peanut Butter Fence, the Polytape Fence and the Offset or Double Electric Fence, the Overhanging, Slanted or Sloping Electric Deer Fence and the Outrigger Deer Control Fence, are not recommended. Slanted or Overhanging Steel Fencing is not of a sufficient height to contain white-tailed deer. Shotguns with Live Ammunition to scare deer is not recommended. Av-Alarm, Ultrasonic Devices, Reflectors and Flashing Lights are not recommended. Hazing by Aircraft is not recommended. Chemical Repellents are not effective for protecting large areas, particularly areas the size of airports.

d. Conclusion

Two themes dominate our analyses of the many techniques for airport deer control. One is that none of the techniques that have been evaluated will work consistently over the long term unless they are applied properly by appropriately trained personnel. This point cannot be overemphasized! Even the best fence designs have limitations that depend on proper installation and maintenance.

The second theme is that there is no one panacea for solving deer problems at airports. As in wildlife control in general, the ultimate solution will usually be to develop an integrated program using several control methods that support the goals needed to be met. At most airports with significant deer problems, this is most likely to include habitat modification, fencing and one or more methods of removing deer that occasionally breach the fence.

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