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

6. Deer Exclusion Techniques

b. Non-Electric Fencing

i. Galvanized Steel Chain-Link Fencing

Description. — Galvanized steel chain-link fencing is the standard type of fence used for security at international and regional airport facilities and is described in detail by the Transport Canada Airport Fencing Manual AK-70-21. This type of fence uses 2.4-m high woven steel mesh that is supported by well-anchored steel posts and topped by three strands of barbed wire using projection-arm supports. Chain-link fencing is also used for deer control along highways by some transportation authorities (Puglisi et al. 1974).

Biological Basis. — The height and strength of the fence provides a physical barrier to deer.

Literature. — The effectiveness of woven steel chain-link fencing has been the standard type of fence against which all other fences to provide security from intrusion to airports by people and wildlife are measured. It also is used as the standard for comparing other less expensive fencing designs due to its high initial cost (approximately $43,000/km). This type of fence is frequently the choice of airport operators in the eastern United States when electric fences have failed to control deer problems (Bashore and Bellis 1982). Game farms, zoos, transportation departments and airports have used chain-link fencing for deer control with success, but deer are capable of jumping over 2.4-m fences if chased (Falk et al. 1978; Novakowski 1984; Lynwood Williamson, National Zoological Park, Washington, DC, pers. comm.), or if winter snow-pack conditions are firm enough to support the weight of deer effectively reducing the height which a deer needs to jump to clear the fence. The performance is also compromised if gaps develop underneath the fence from frost heaving, soil erosion or digging by canids or other animals. Deer have been found to be capable of crawling through fences if the gap is greater than 20 cm (Bellis and Graves 1978, Falk et al. 1978). Drainage ditches can also provide access under perimeter fences. Chain-link fencing of 3 m without barbed wire has been in use at Alpena County Regional Airport, for many years (Lee Scherwitz, Airport Manager, Alpena County Regional Airport, Alpena, MI, pers. comm.) and has generally been successful in excluding deer. However, some white-tailed deer have occasionally entered the enclosed area by jumping the fence when frightened by vehicles.

Recommendation. — Recommended as an effective, long-term control measure for deer and other large mammals at airports, but costs may be prohibitive.

Literature Reviewed. — Falk et al. 1978; Bashore and Bellis 1982; Novakowski 1984.

ii. High-Tensile Fixed-Knot Fencing

Figure 10. A high-tensile fixed-knot deer fence (from Craven and Hygnstrom 1994).

Figure 11. A stream-crossing structure using high-tensile fixed-knot deer fence (from Craven and Hygnstrom 1994).

Description. — High-tensile fixed-knot fencing has been used for wildlife control to protect orchards and high value crops (Craven and Hygnstrom 1994), highways (Puglisi et al. 1974) and airports, as well as for enclosing white-tailed deer at game farms and is described by the Transport Canada Airport Fencing Manual AK-70-21 as Watchman Type fence. This type of fencing is specifically designed for wildlife exclusion in areas where chain-link fencing could disrupt operation of Instrument Landing Systems (ILS). Current market brands for this type of fencing are Solidlock® and Tightlock® and are designed for controlling a variety of wildlife including deer, elk, moose, wolves and coyotes. Solidlock® fence uses high-tensile horizontal wires that have variable spacing, from 7.6 to 15.2 cm apart in the lower half of the fence where contact by deer is more frequent and 17.8 cm apart in the upper half of the fence to reduce cost. Vertical stay wires are spaced either 15.2 or 30.5 cm apart. Horizontal fence tension is maintained by deep crimps in the horizontal wires and by strongly designed corner bracing. Game farms use the 15.2-cm spacing and top the woven fence with three additional strands of high-tensile wire along the top to increase the fence height to 3-m (Figure 10). Solidlock® fence is marketed for use at airports in 2.4-m and 3.7 m heights. Galvanized steel pipe or pressure-treated wood posts are used to support the woven fence. Posts are reinforced at the ends and corners of the fence to maintain wire tension. Distance between posts varies between 6 m and 7.6 m. High-tensile fixed-knot fencing is also used for deer control along highways by transportation authorities (Puglisi et al. 1974). This type of fence is expected to last 20 to 30 years with maintenance that is limited to soil erosion control. Costs (approximately $30,000/km) for 3-m high fence are higher than high-tensile electric fencing, but are 30 percent lower than the cost of chain-link security fences.

Biological Basis. — The barrier fence height and tightly locked wire prevents deer from crawling underneath or squeezing through the fence. The tight knots and high tension of fixed-knot fencing secures the vertical and horizontal wires together and prevents deer from distorting the mesh and squeezing through the fence. The extra strands of high-tensile smooth or barbed wire, supported by angled extensions above the woven fixed-knot mesh, extends the protection to 2.8 m. The 3.7-m tall fence offers still higher protection. The jump height of white-tailed deer is over 3 metres. Therefore the 3.7-m height type of fence should offer significantly higher protection. The standards for airport deer fencing should acknowledge this.

Literature. — Different heights and styles of high-tensile fixed-knot fencing have been used to exclude deer. Craven and Hygnstrom (1994) consider this type of fence to be deer-proof. The weakness of the design occurs where terrain is uneven and deer can crawl under the fence. Structures using this type of fencing have been developed to ensure resistance to soil erosion at stream crossings and uneven terrain (Figure 11) (Blair et al. 1963; Halls et al. 1965). On flat terrain the addition of a 1-m page wire fence folded to a 90 degree angle along its length and attached at the bottom of the fence with hog rings and laid outward on to the ground attached with wire stakes keeps canids from digging holes under the fence (John Kerkvliet, President, Ontario White-tailed Deer Producers’ Association, pers. comm.). White-tailed deer game farms that use the 2.8-m high fence design have reported that this design is successful in keeping farmed deer inside and wild deer outside (John Kerkvliet, pers. comm.). The Alberta Department of Agriculture, Food and Rural Development’s standard for deer farms is 2.8 m of mesh wire or 2.4 m mesh wire topped by at least two high-tensile wires with a maximum spacing of 15 cm between wires. Eric Falk (publisher, Canadian Elk and Deer Farmer, pers. comm.) indicated that this design is capable of keeping wild white-tailed deer out of game farms. The fencing standard for deer farms set by the Michigan Department of Agriculture is 3 m. The minimum fencing requirements for farmed deer in Ontario is fixed-knot wire fencing with a minimum height of 2.44 m.

Recommendation. — The 3-m game fence design using smooth high-tensile wire to add height to the 2.44 metres of fixed-knot high-tensile wire mesh is recommended for control of deer at airports. In areas of high deer populations or movement, the 3.7-m tall fence is recommended.

Literature Reviewed. — Blair et al. 1963; Halls et al. 1965; Craven and Hygnstrom 1994; Puglisi et al. 1974; Transport Canada Airport Fencing Manual AK-70-21.

iii. Slanted or Overhanging Steel Fencing

Figure 12. The Slanting, or Overhanging, net-wire deer fence (from Palmer et al. 1985).

Description. — The slanted or overhanging fence design was developed to reduce depredation by deer at orchards and agricultural crops. The "California Sloping Wire" fence design described by Longhurst et al. (1962) consists of a 1.8-m high steel square-mesh fence attached to the ground with stakes along the bottom and supported by the tops of 1.4-m-tall wooden posts along the top edge (Figure 12). The mesh is 22.5 cm x 22.5 cm. The fence is constructed so that it slopes outward from the enclosed area. Bonwell (1983) indicated that this fence design produces a "good physical and psychological barrier". This design is generally less costly than other types of steel mesh fencing because the post height is shorter. No current cost estimate is available, but a cost comparison in Longhurst et al. (1962) determined that cost was 40% of 2.44-m chain-link fencing.

Biological Basis. — This type of steel-mesh fence uses the sloped arrangement of wires where the deer that approach from outside of the fence encounter the high part of the slope. This encourages deer to try to crawl under the fence and discourages jumping. The three-dimensional shape of the slanted fence is intended to reduce the likelihood of deer jumping over the fence because the mesh slopes over the area where a jumping deer would likely land. The anchored steel mesh blocks deer that attempt to crawl under the fence.

Literature. — Palmer et al. (1985) tested the effectiveness of the California Sloping Wire Fence design during 30-day experimental periods at the Penn State University Experimental Forest to protect understory growth. They found that deer were capable of penetrating this design. It is possible that higher sloped-mesh fence designs would offer better control of deer, but no literature is known to have evaluated them.

Recommendation. —The Sloped steel mesh fence design is not recommended because it is unable to control deer. Recommendation of higher designs of sloped mesh fencing depends on further evaluation.

Literature Reviewed. — Longhurst et al. 1962; Palmer et al. 1985.

iv. Plastic Mesh Deer Control Fencing

A variety of plastic mesh fences have been developed to protect orchards, tree plantings, crops and residential properties and for use as fences at airports in areas where ILS installations have prevented the use of steel fence materials. The most promising type of plastic fencing is an extruded polypropylene animal control fence, manufactured in Italy by Tenax® SpA, and is marketed by Fickle Hill Fence and Supply, Arcata, California, and Benner’s Gardens, Inc. New Hope, Pennsylvania in the United States. At the time of writing of this report there was no Canadian distributor of this type of fence.

Description. — Tenax® C-Flex polypropylene plastic fencing is 2.3 m tall and available in "Standard" and "Heavy Duty Perimeter" types. It is marketed for agricultural and residential use to exclude deer. The Standard type has a mesh size of 5.7 x 7 cm and the Heavy Duty type has a mesh size is 3.8 x 3.8 cm. The plastic mesh of both types is made of 2- to 4-mm extruded black polypropylene. The Heavy Duty type is reported to be 65% stronger than the standard type due to the tighter mesh. The mesh is intended to be supported by steel rebars, wooden or steel posts or trees spaced 3 m to 4.5 m apart. The fence mesh is fastened to the supports by self-locking polypropylene ties. Deer are prevented from crawling under the fence by stakes that hold down the bottom of the fence. It is lighter than steel wire fencing; therefore, the distance between posts can be longer. Benner’s Gardens Inc. markets polyester-coated 4.1-cm diameter steel posts and corner braces for use with this fence that are more easily installed than wooden posts. The fence material is more flexible than steel wire mesh and follows the ground contours more readily. This fence also requires enough tension to prevent the fence from sagging. Benner’s Gardens, Inc. recommends that a nylon cable be strung along the top of the mesh and along the middle of the mesh if plant growth such as vines adds weight to the fence and causes the fence to sag. The nylon cable is tensioned and then fastened with cable clamps. The polypropylene is treated for UV light resistance and has an expected life span of 10 years and should be inspected for damage and repaired weekly. Repair is simple. Tears can be sewn with the polypropylene ties and holes can be patched by sewing a panel of the fence material over the hole with ties. Glenn Siegfried (Fickle Hill Fence and Supply, pers. comm.) indicated that neither type of fence has been used for deer control at airports or game farms. Cost for this type of fence, using steel-pipe posts and braces is estimated to be $7,000/km, excluding installation costs.

Biological Basis. — The height of the fence provides a physical barrier to deer. The low visibility reduces the likelihood of attempts to jump over the fence.

Literature. — No independent tests of the Plastic Mesh fencing have been reported. The above description is based solely on material from the manufacturer and suppliers. Benner’s Gardens, Inc. has documentation of the owner’s garden that has been protected by the standard type of fencing for at least 8 years without deer damage to the garden. No report of breakage of the heavy duty type has been reported to Benner’s Gardens Inc. since sales began in the spring of 1996. The heavy duty type was developed to prevent breakage by direct collisions by running deer. No evaluation of resistance to chewing damage by other types of wildlife (i.e. rodents and canids) has been done.

Recommendation. — In the absence of any independent testing of this product, it is not possible to make a recommendation of either the standard type or the heavy duty type of Tenax® fencing. This fence has potential to be an effective means of deer control, but tests and impartial documentation are needed.

Literature Reviewed. — Marketing and technical documentation provided by Benner’s Gardens, Inc. New Hope, Pennsylvania; Fickle Hill Fence and Supply, Arcata, California; and Tenax® Corporation, Baltimore, Maryland.

v. Barrier Accessory Equipment

Many airports that have installed perimeter fencing to exclude deer continue to have problems with deer entering through gates that must remain open for vehicle traffic. Cattle gates (also called cattle guards) have been used at airports to prevent this from occurring (Bashore and Bellis 1982).

Description. — Cattle gates have been used to prevent access by livestock through openings in fences for many years. A steel frame as wide as the opening of the fence and 2 to 3 metres long is spanned by many 7.6 cm steel pipes aligned parallel to the gate opening and fixed to the frame at 12.7 cm intervals to form a pipe platform with 5 cm spaces between the pipes. The pipe platform is placed in a rectangular excavation dug in the ground at the gap in the fence. The application of cattle gates at the openings of deer fences is intended to increase the effectiveness of deer fencing, especially at openings where control gates would be left open to allow vehicular traffic to pass.

Biological Basis. — Deer do not use cattle gates due to poor footing on the structure; their hooves slide between the pipes if they attempt to pass over it.

Literature. — A test of mock-ups using PVC pipe attached to a wooden frame over 0.5-m and 1.0-m deep excavations found that there was an 88 to 98% reduction of the number of deer crossing the fence openings (Belant et al. 1998a). The 1.0-m deep excavation was recommended to prevent possible contact of the deer’s feet with the bottom of the excavation and to accommodate moderate to high snowfall accumulations. Without the extra depth or snow removal, snow could fill the cattle gate to a level that would allow deer to cross easily. Belant et al. (1998a) also recommended the installation of fencing immediately adjacent to and along the entire length of the cattle guards to maximize their effectiveness.

Recommendation. — Recommended to complement deer fences where gates must be left open for vehicular access. Fencing along the length of cattle gates is highly recommended.

Literature Reviewed. — Hoy 1982; Belant et al. 1998a.