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Deer Exclusion Devices and Deterrent Techniques

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

6. Deer Exclusion Techniques

c. Deer Removal Methods

When fences do not provide complete exclusion of deer, either due to design limitations or fence damage, deer must be removed from the enclosed area. This can be done by a variety of means. One-way gates, deer jump ramps and deer leaps are passive methods that can be incorporated into a perimeter fence. Other methods involve removal by drives and live traps and re-location. Shooting with live ammunition may be necessary in some situations.

i. One-way Gates

One-way deer gate (top view)

Figure 13. Top view of one-way deer gate (from Reed et al. 1974).

One-way deer gate (front view)

Figure 14. Frontal view of one-way deer gate showing plans and specifications (from Reed et al. 1974). Patent pending.

Design for installation of one-way deer gate

Figure 15. Possible design for installation of one-way deer gates at outside corners of an airport perimeter fence. The design places a gate directly in front of the animals as they move along the fence (top view) (adapted from Reed et al. 1974 and Canada Flight Supplement 1995).

Description. — One-way gates have been used in the United States and Canada to allow the movement of deer that have crossed highway barrier fencing into the traffic right-of-way to return back outside the fence structure. One-way gates prevent deer on the highway side of the fence from being trapped on the highway right-of-way. The construction consists of spring-steel bailer tines that are hinged and arranged to form a funneling valve that permits easy passage from one side and difficult or no passage from the other side (Figures 13 and 14) (Reed et al. 1974). The use of effective one-way gates would not only reduce the effort required to remove deer that have managed to cross an airport fence, but also allow deer to be removed from the airport without being trapped and handled thus reducing the potential for accidental mortality. Costs for one-way gates could not be determined from the literature.

Biological Basis. — When deer encounter a fence, they often follow it until they find a gap that enables them to pass through the fence and continue in their intended direction. One-way gates are positioned at 90-degree angle offsets in the fence (Figure 15) so that when a deer follows the fence it will find the gate and pass through to the outside of the fenced area.

Literature. — Reed et al. (1974) tested a promising one-way gate design in a 2.44-m highway fence along an Interstate Highway near Vail, Colorado during 1970-72. They found that 96% (558) of passages by mule deer were in the one-way direction for which the fence was designed. This study estimated that eight gates located along both sides of a 2.4-km fenced section of the highway permitted an estimated 223 deer to escape the highway right-of-way. Lehert and Bissonette (1997) found one-way gates to be less effective for mule deer during tests of a highway crosswalk design, but the one-way gates were completely effective in controlling the direction of deer passage. Only 16.5% (40) jumped through the gate to leave the right-of-way. The other 203 deer remained within the right-of-way until they found other means of leaving, either by walking along the fence to the end, jumping back over the fence or by being struck and killed by highway traffic. Of the 128 deer that approached the one-way gates from the wrong-way direction, none passed though it to enter the highway right-of-way. These two studies indicated that the orientation of the gates to the fence was an important consideration in their overall effectiveness. Phillips (1999) commented that maintenance of one-way gates has been a problem along highway fences that are exposed to harsh and cold weather in New Brunswick. Frost action heaves the fence posts that support the gates and maintenance is then required to re-align them. Also the hinges for the tines of the one-way gates require lubrication with low temperature grease to offset seizing from weathering or extreme cold. Phillips (1999) also described the behaviour of panicked deer along the right-of-way of the highway. Running deer did not recognize the one-way gates as escape routes after being frightened by motorists that had stopped to admire them. Rather, the deer charged the fence until they became exhausted or seriously injured and died or had to be euthanized. The orientation of the one-way gates was being reviewed to improve their operation when Phillips (1999) was published.

Recommendation. — One-way Gates are recommended to permit deer to leave airport fenced enclosures that they have previously penetrated. Proper design and location are important to ensure successful operation. One-way Gates require additional maintenance and may be expensive.

Literature Reviewed. — Reed et al. 1974; Lehert and Bissonette 1997; Phillips 1999.

ii. Deer Jump Ramps

Description. — Earthen jump ramps for deer have been used to permit deer to escape wildlife fences located along highway right-of-ways in Wyoming.

Biological Basis. — Once deer have encountered a fence, they follow it until they find a means to cross it. The earthen ramp on the inside of the fence allows the deer to walk up and jump over the fence to escape the area enclosed by the fence.

Literature. — Lehert and Bissonette (1997), disappointed with the performance of the one-way deer gates in their study suggested the use of earthen ramps or other types of ramps to enable deer to jump the fence and return to the area outside of the fence. H. Harju (Wyoming Game and Fish pers. comm., cited by Lehert and Bissonette 1997) indicated that earthen ramps are used successfully in Wyoming. Maintenance of this device appears to be limited to soil erosion control.

Recommendation. — More information is needed about use of earth ramps in other situations and areas before they can be recommended for use at airports. However, earth ramps promise to be an inexpensive and effective method of providing one-way passage for deer. In addition, the ramps would be relatively maintenance free.

Literature Reviewed. — H. Harju, Wyoming Game and Fish pers. comm. (cited by Lehert and Bissonette 1997).

iii. Shooting

Description. — Killing is an efficient method for handling deer that enter airside through perimeter fences. Bait, such as shelled corn and alfalfa, can be used to draw deer close to a location where deer can be shot and removed from the airport property.

Biological Basis. — Deer are drawn to areas away from airport operations areas and shot.

Literature. — Ishmael and Rongstad 1984 found that when compared to live capture methods, shooting over bait was the least labour-intensive removal technique, resulting in a cost of $73.95 (US) per deer in 1984. It also required the lowest effort at only 13.5 person-hours per deer. The best results were obtained shortly after fresh snowfalls when locations of deer activity and deer paths could be found quickly. In many situations, public objections to killing deer are likely to prevent this method of deer removal (Loker et al. 1999). There are also concerns about using rifles on active airfields.

Recommendation. — Recommended as a deer removal technique, particularly during winter and early spring when deer can be baited.

Literature Reviewed. — Ishmael and Rongstad 1984; Loker et al. 1999.

iv. Chemical Immobilization

Description. — Chemical immobilization can be used to sedate deer to allow them to be removed from an airport. Many airports that serve urban centres have a policy that deer will be killed only as a last resort. Chemical immobilization is a means of humanely and quickly capturing deer and relocating them or killing them, in certain circumstances. A deer that has been shot and only injured can run wildly around an airport thereby compromising aircraft safety. For chemical immobilization, deer are darted using a .22 caliber rifle, CO2 or compressed air gun to fire a dart containing a dose of a fast-acting sedative that rapidly immobilizes the deer. The Minneapolis-St. Paul Metropolitan Airports Commission wildlife control staff uses the Pneu-Dart Model dart rifle equipped with a 4X scope that delivers a 1-mL dose of succinylcholine chloride, a muscle relaxant, to the deer (Ostrom 1998). Succinylcholine chloride is a fast-acting (<10-min.) muscle relaxant that is effective in small amounts. Anectine is a trade name of this compound. It is relatively safe when handled and dosed correctly and is not effective if consumed orally. It is also short-lived; therefore, animals that are not captured will recover rapidly if they have been dosed correctly. This compound is currently not permitted for wildlife control in Canada due to dangers associated with its use (Bruce MacKinnon, pers. comm.). Over-dosage of succinylcholine chloride causes respiratory paralysis and death. Under-dosage will not effectively sedate the deer and result in a panicked response. Effective dosage requires the skill of an experienced wildlife anesthesiologist. The delay before the tranquilizer takes effect on the deer can result in danger from erratic running. Accidental injection of people has resulted in death. Hawkins et al. (1967) has described other means of deer capture using chemical immobilization. Any airport manager that considers the use of chemical immobilization agents should consult with experienced natural resource ministry staff for regulations.

Biological Basis. — Chemical immobilization sedates deer to enable humane removal or euthanasia.

Literature. — Of the methods used to deliver the chemicals, the crossbow was found to be the most efficient in terms of person-hours required to capture deer (Hawkins et al. 1967). It has initial low-cost, a reasonable accuracy up to about 45 metres, and delivers an inexpensive syringe-dart. Use of chemical immobilization for relocation of deer to areas away from airports is an expensive alternative to killing and survival rates of relocated deer are low (Montoney 1994).

Recommendation. — Chemical immobilization to facilitate removal of deer from airports has a limited recommendation because of the dangers involved. Use of succinylcholine chloride in Canada is not permitted. Other anesthetic agents may be used providing that its use is coordinated with and permitted by natural resource ministry staff. Airport staff must be properly trained and airport safety must be maintained. Chemical immobilization is particularly useful at airports where lethal control is either unsafe or publicly unacceptable, where deer do not pose an immediate threat to aircraft operations, and where deer populations outside of airport grounds do not approach carrying capacity and the likelihood of survival of the relocated animals is high.

Literature Reviewed. — Hawkins et al. 1967; Montoney 1994; Ostrom 1998.

v. Live Traps

Description. — Live traps designed to capture deer for relocation include corral traps and wire box traps. Corral traps are circles of 3-m high fencing wire mesh with a 30-m to 75-m circumference and are supported by nailing to trees (Hawkins et al. 1967). A single door is hinged at the top and opens inward; it is triggered to close behind entering deer. The cost of the materials in a corral trap is modest. Wire box traps are baited to attract deer. Stephenson box traps are wire boxes (1.2 m wide, 1.2 m high and 3.7 m long) that trigger shut when a deer has entered the trap (Hawkins et al. 1967). Cohick-type (Peery 1968) and Clover (Clover 1956) box traps are similar to Stephenson traps, but with differing trigger mechanisms. Addition of radio transmitters to the door trigger (Hayes 1982) provides an automatic notification of capture and reduces the time that the trap confines deer. Both corral and box traps are baited to attract deer. The trapped deer are tranquilized and relocated by trained wildlife managers.

Biological Basis. — Deer are attracted to bait that is placed within the trap and a triggered door closes behind the deer.

Literature. — A comparison of methods of capturing white-tailed deer (Hawkins et al. 1967) found that trapping was the most efficient capture method during periods when food was scarce and deer could be baited. Corral traps and box traps required less time to capture each deer than other relocation methods when food was scarce and deer could be baited. When food was abundant, the crossbow, Cap-Chur equipment, and longbow, in that order, produced better results. The corral trap could trap up to four deer at a time, but mortality was 13% (42 of 302 captures) during 611 nights of trapping. The box traps captured 47 deer during 131 nights of trapping but with 0% mortality (0 of 47 captures). The box traps trapped only one deer at a time. A deer removal program described by Palmer et al. (1980) found that Stephenson traps took 2.8 person-hours per deer captured. Peery (1968) found Caslick-type traps to be less effective, but Ishmael and Rongstad (1984) attributed this to greater food availability. In 1984 the cost of deer removal using five Clover traps was $569.77 (US) per deer (Ishmael and Rongstad 1984). For comparison, shooting over bait removed 34 deer at a cost of $73.95 (US) per deer.

Recommendation. — Corral and box traps are recommended for deer removal or relocation during winter and early spring when deer can be baited. Performance of live traps normally declines, as food becomes more abundant; however, at airport situations the effectiveness of traps may remain high because they can be located along the perimeter fence and capture deer as they follow the fence line. Live traps require the expertise of professional wildlife biologists. Mortality during and after capture and lack of suitable relocation sites often limits the effectiveness of live capture and relocation.

Literature Reviewed. — Clover 1956; Hawkins et al. 1967; Peery 1968; Palmer et al. 1980; Hayes 1982; Ishmael and Rongstad 1984.

vi. Drive-netting

Description. — A deer drive involves chasing deer into a portable net where the animals are live captured. A portable, 15-m long, rectangular, nylon cord net with 17.8-cm mesh is extended from a vehicle, or quickly raised by a number of people and deer are directed into the net by people blocking potential exit routes (Ishmael and Rongstad 1984; Silvy et al. 1975). This may also be done with improved effectiveness using lights at night.

Biological Basis. — Deer are actively captured alive with a portable net by trained wildlife biologists. The captured deer are subdued by tying their feet and blindfolded and relocated.

Literature. — Ishmael and Rongstad 1984 found that when compared to other methods, drive-netting was the most labour-intensive live-capture technique. In spite of the high effort, drive-netting is considered to be one of the better live-capture methods. Large numbers of trained people are needed to make this technique work. Best results are obtained shortly after fresh snowfalls when locations of deer activity and deer paths can be found quickly.

Recommendation. — Recommended as a deer removal or relocation technique during winter when fresh deer tracks assist in locating deer. Deer drives are recommended when many deer need to be removed alive in a short period of time. This method requires the expertise of a professional wildlife biologist; its cost may be prohibitive due to the large numbers of people required for the deer drive. Mortality during and after capture and lack of suitable relocation sites often limits the effectiveness of live capture and relocation.

Literature Reviewed. — Silvy et al. 1975; Ishmael and Rongstad 1984.

vii. Required Permits

All deer removal programs require that permits to capture and/or kill deer must be obtained from the appropriate authorities. Provincial natural resources ministries issue deer removal permits to airport wildlife managers for airports experiencing deer problems. The use of guns to kill deer requires the airport to have a valid deer removal permit, an experienced, licenced deer hunter with a valid Firearms Possession and Acquisition Licence (PAL) and using a registered shotgun or rifle. Arrangements to implement the deer removal permit should be co-ordinated with the provincial natural resources ministry for killing deer and carcass disposal. Carcasses may be used for human consumption if permitted by the provincial health ministry. The use of tranquillizing drugs to capture deer requires involvement of provincial natural resources ministries to acquire and use drugs, permit and co-ordinate live-capture and relocation of deer.

Date modified:
2010-05-03