In addition to deer exclusion fences, other deterrent techniques can be used to frighten deer away from airport runways. Such techniques may be most useful at airports that already employ bird control personnel to patrol the airport. Several techniques have been used with variable success to control deer at airports. Craven and Hygnstrom (1994) indicated that the key to success when using frightening methods and repellents is to use them at the first sign of a deer problem. Once deer become used to foraging at the airport, it often is more difficult to drive them away. The techniques also become less effective if deer are allowed to habituate to them.
In most cases, the use of deer deterrent techniques should be used only to provide temporary control until a more permanent solution, such as fencing, removal or killing, can be found.
The classification of the following products and techniques as auditory deterrents is somewhat arbitrary. Many of these products also present visual stimuli to deer and, to some extent at least, deer respond to those visual cues as well as to the sounds.
A number of auditory devices and methods have been developed to deter deer from agricultural crops and airports. The general obstacle to the use of sound for effective animal control is habituation. Many animals adapt to new sounds and learn to ignore them if they are not associated with real danger. Deer also habituate to noise and movement around airports, just as they often do when they occupy habitats adjacent to highways. Bashore and Bellis (1982) described the activities of deer at Eglin Air Force Base in Florida where deer were feeding on grass between parallel runways and leisurely crossing runways while jets were preparing for take-off. "F-4s, F-102s and other aircraft would ignite their afterburners, which resounded with a loud, booming noise and would speed past the deer, which went on feeding, undeterred by noise and motion." Habituation of deer to human activities and noisemakers creates a problem for the use of auditory deterrents. In areas where seasonal hunting has been permitted, deer often learn to avoid the sound of gunfire. However, if the sound of gunfire is not associated with real danger, deer habituate to it.
Shotguns, when fired into the air, produce a loud bang, then a "whirring" noise that may disperse deer whether or not some deer are hit and killed. (A rifle should not be used in this manner, given the potential hazard to people at distances of 2-3 km or greater.) Shooting has been used to frighten or kill deer in agricultural fields (Craven and Hygnstrom, 1994), and at airports (Lee Scherwitz, pers. comm.). In these situations, deer are often killed to reinforce the effectiveness of non-lethal deer scaring devices. Other pyrotechnic devices can be at least as effective as "shooting to miss" with live shot. Hence, it is doubtful that live shot should be used primarily to scare deer from an airfield. Deer that are subject to hunting tend to be more easily frightened by the sounds of shotguns and pyrotechnics.
Recommendation. — Scaring using live ammunition is not recommended for deterring deer at airports, except in particular situations where the deer are actively hunted and react to the sounds of shotguns.
Pyrotechnics include a wide variety of noise-making shells fired from shotguns, starter pistols, and flare pistols. They include shellcrackers, flares, firecrackers, rockets, and mortars. Pyrotechnics consist of bangers and crackers that emit loud, banging, gun-like noises, and screamers and whistlers that produce continuous noises and flashes of light. Pyrotechnics are widely used at airports to scare birds, and often used to scare deer. The explosions from bangers sound like gun blasts, but the noise occurs at the end of the trajectory near the deer rather than at the start of the trajectory as for a regular shotgun shell. Again, this type of auditory deterrent will be more effective in areas where deer are regularly hunted.
Pyrotechnics are the most commonly used wildlife control device on airports. Pyrotechnics can and do scare wildlife but, without effective presentation, animals commonly habituate to the loud bangs. Presentation is the critical factor. Therefore, pyrotechnics must be deployed by personnel that are skilled wildlife controllers. Because of their portability and flexibility of use, pyrotechnics that are fired from shotguns or pistols are the most effective type.
FOD (foreign object damage) can be a concern with shotguns and pyrotechnics used near active runways. It is important to remove shells and shell casings from areas where they may be sucked into jet engines (Jarman 1993).
Recommendation. — Pyrotechnics are not recommended for permanent control of deer at airports. However, they can provide effective short-term control, especially when deployed by trained personnel. Habituation will quickly develop and more permanent solutions should be found.
Gas cannons and "exploders" are gas-powered devices that produce periodic very loud, banging noises, which frighten birds and deer. The "bangs" are produced by igniting gas (usually propane). The noise of the explosion resembles, or is louder than, that of a 12-guage shotgun (Nelson 1990a). Blasts are emitted at adjustable time intervals (Salmon and Conte 1981, Salmon et al. 1986), sometimes close together, controlled by an automatic timing device. A photocell can be included to turn the system off at night. Some gas cannons can be set to fire at random intervals and to rotate after each explosion so that subsequent shots are aimed in different directions. Remote control firing mechanisms are also available whereby a person can directly control the timing and number of shots from a distance. Remotely operated cannons can also rotate after each shot.
The sudden, loud bang from a gas cannon is capable, at least initially, of scaring deer away from an area. This flight response is probably related to the similarity of the bang to that of a shotgun shot, particularly in areas where deer are hunted. However, without reinforcement that the bang represents a potential threat, deer soon habituate to the sounds.
Little literature was available for evaluation of the effectiveness of gas cannons for use to control deer. Gas cannons can be more effective at dispersing deer if the frequency of the explosions is varied and if the cannons are moved every second or third day of use to a different area. Raising gas cannons off the ground on platforms (Craven and Hygnstrom, 1994) can increase the effective noise level. Belant et al. (1996) found that motion-activated exploders, triggered by passing deer were more effective than exploders that fired at regular intervals. Thus, the exploders only fired when a deer was close by, which made habituation less likely. Cannons must not be deployed near fuel because the igniter for the cannon could ignite the vapour.
Recommendation. — The use of gas cannons is not recommended as a method of deterring deer at airports. The small effective radius of motion-activated exploders and the large size of airport runways makes the effective use of propane exploders impractical.
Av-Alarm is an electronic noise-making product that was designed to frighten and repel birds from agricultural crops and airports. It has also been applied to frighten deer from airfields. It projects irritating noises in a flat, outward pattern in an effort to repel birds and other wildlife. Av-Alarm is not effective for deterring birds (Harris and Davis 1998). Efforts by the manufacturer to extend the applications of this product to repel deer have been ineffective (Stewart 1974).
Recommendation. — Av-Alarm is not recommended for repelling deer from airports.
Ultrasound is normally defined as sound at frequencies too high to be detected by humans. The upper limit of human hearing is generally around 20,000 Hz, although few adults have effective hearing at frequencies that high. The obvious advantage of ultrasound as a dispersal or deterrent technique, if it were effective, would be that it would not be audible to humans.
There is no evidence that ultrasound repels animals better than audible sound (Bomford and O'Brien 1990). The high frequency ultrasound dissipates rapidly, thereby requiring more energy to produce significant coverage. Mammalian species, including rodents, bats and dogs are known to detect ultrasound, but no established aversive response has been demonstrated (Hurley and Fenton 1980, Blackshaw et al. 1990, Bomford and O'Brien). Evaluation of three ultrasonic frightening devices by Belant et al. (1998b) found that motion-activated Yard Gard, and Electronic Guard, did not deter deer from corn feeding stations and that motion-activated Usonic Sentry (without strobe) was capable of reducing corn consumption for up to one week, after which deer habituated to the ultrasound. Deer expressed "alert" or "nervous" behaviour during the trials by Curtis et al. (1997) when ultrasound was emitted, but feeding was not interrupted. These tests concluded that ultrasound alone was ineffective in deterring white-tailed deer.
Recommendation. — Ultrasonic-emitting devices are not recommended for deterring deer from airports.
A variety of reflective devices have been claimed to deter deer from highway right-of-ways. The majority of devices are mirrors attached to posts along the highway where they reflect the light from the headlights of approaching cars. The reflected light then alerts any deer near to the highway of the danger. There are a number of types of warning reflectors. In North America, the "Van de Ree" and "Swareflex" have been evaluated for use along highways to prevent deer-vehicle collisions. The use of these reflectors along highways has been generally unsuccessful (Gordon 1967, 1969; Waring et al. 1991; Romin and Bissonette 1996; Putnam 1997). The potential use of flashing lights to deter deer at airports is analogous to the use of highway reflectors.
Recommendation. — Reflectors or flashing lights are not recommended as a potential deer deterrent at airports.