Auditory Deterrents

• Shotguns and Rifles with Live Ammunition
• Pyrotechnics
• Shotgun-based
• Flares
• Pistol-based
• Rockets and Mortars
• Gas Cannons and "Exploders"
• Agri-SX
• Bird Gard AVA and Bird Gard ABC
• Av-Alarm
• Distress and Alarm Calls
• Calls of Predators
• High Intensity Sound
• Ultrasonics
• Aircraft Engine Noise and Infrasound

The classification of the following products and techniques as auditory deterrents is somewhat arbitrary. Many of these products also present visual stimuli to birds and, to some extent at least, birds respond to these as well as to the sounds.

Shotguns and Rifles with Live Ammunition

Shotguns and rifles, when fired into the air, produce a loud bang, then a "whirring" noise that may disperse birds whether or not some birds 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 birds at fisheries operations (Lagler 1939; Davidson 1968; Anderson 1986; NCC 1989), in agricultural fields (Nomsen 1989), and at airports (DeFusco and Nagy 1983; BSCE 1988). In these situations, birds are commonly killed. In most cases, this is done mainly to reinforce the effectiveness of non-lethal bird scaring devices that are also in use, not in an attempt to kill a significant proportion of the birds present. Other pyrotechnic devices would probably be at least as effective as "shooting to miss" with live shot. Hence, it is doubtful that live shot should be used to scare birds from an airfield unless it was the only technique readily available. (See also "Live Ammunition-Shooting" later.)

Shotguns produce their loudest noise at the gun which may be 50-100 m from the birds, whereas the noise from the pyrotechnics occurs very close to the birds. Thus, live ammunition is not a very effective deterrent.

Birds habituate to shots, especially in the case of species that are not widely hunted. For example, shooting at cormorants and herons, and killing some of them, only temporarily repelled the species from fish farms (EIFAC 1988; Coniff 1991). Shooting was not effective in dispersing egrets from airports; most egrets returned shortly after being shot at, even if some birds were killed (Burger 1983; Fellows and Paton 1988). Shooting also was not effective in dispersing roosting geese (Taylor and Kirby 1990).

Ammunition for a 12-gauge shotgun (and the cost to deploy a person to use the shotgun) is expensive in comparison to the low operating costs of exploders, which are discussed below. However, a shotgun is more easily deployed. There would be a safety concern in using live shotgun ammunition in an area where airport activities were underway; however, the maximum distance that shotshells could injure people or birds is 60-90 m, depending on the size of the shot being used. Thus shotguns do not have the potential to injure at long range like rifles do.

Pyrotechnics

Description. – 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. They all emit loud, banging noises, produce flashes of light (and therefore also have a visual deterrent component), or both. Pyrotechnics are widely used at airports to scare birds.

Biological Basis. – The banging noise from some pyrotechnics resembles that from a shotgun. That resemblance no doubt enhances the effectiveness of these devices in scaring birds that are hunted. Pyrotechnics also produce startle reactions in birds. However, birds can gradually habituate to pyrotechnic devices. Other supplementary scaring techniques, including the occasional shooting of a bird with live ammunition, are often used to reduce the rate of habituation to pyrotechnics.

Shotgun-based

Scare or Bird Frite cartridges, commonly referred to as cracker shells, are usually deployed from 12-gauge shotguns. A single shot or pump action gun with a short barrel and no choke should be used for safety reasons. Shellcrackers contain a firecracker that is projected approximately 45-90 m (50-100 yd) and then explodes (Mott 1980; Salmon and Conte 1981; Littauer 1990a). This has the advantage of being able to place the explosion closer to the birds. The noise from the explosion frightens the birds causing them to flush or change flight direction.

Exploding shells have proven useful in repelling and dispersing birds at airports (Burger 1983; DeFusco and Nagy 1983; BSCE 1988), at landfill sites (Southern and Southern 1984; Davis and Davis 1994), in fruit orchards (Nelson 1990b), and on cereal crops (Booth 1983). Shellcrackers have longer range than do smaller cartridges launched from starter's pistol (see below). This can have the advantage that less manpower is required to cover an area (Mott 1980). When fish-eating birds are dispersed from aquaculture ponds by shellcrackers, the effect is relatively short-term: most birds are deterred from returning for a few hours to a few days (Draulans 1987). In a few rare situations, birds have been prevented from returning for longer periods (up to four weeks) before habituation took effect.

At some times in the past, shellcrackers have been difficult or impossible to obtain at short notice. Thus, if this method is to be applied, an adequate supply of shellcrackers should be kept in stock as a contingency measure. Hussain (1990) recommended caution in using shellcrackers in areas of dry vegetation where fires can start. This is also a concern around fuel.

Flares

Flares are modified shotgun shells, fired from a pistol or shotgun, or brightly burning firecracker-like devices that can be deployed from hand-held launch units or placed on the ground to burn. When fired, the flare leaves a trail of smoke that may frighten birds (Koski and Richardson 1976). Flares are not as effective as cracker shells. However, when used in conjunction with other deterrent methods, flares might be useful in influencing the direction in which birds disperse, although there may be a fire hazard in some situations.

Pistol-based

Pyrotechnics can be fired as far as 25 m into the air from a 15 mm flare pistol or a 6 mm blank pistol. Firecrackers are commonly called noise, bird, whistle, or clow bombs (Mott 1980; Salmon and Conte 1981; Salmon et al. 1986). Pistol-based pyrotechnics have a shorter range than do shotgun based shellcrackers.

Small pyrotechnic shells launched from pistols include "bangers", "screamers or whistlers" and "crackers". They are widely used in deterring birds from airports, agricultural areas, and landfill sites (e.g. Miller and Davis 1990a,b). Because these devices can be fired into the air toward birds, they are the most useful of the firecracker-type deterrents. However, in general they have shorter range than do 12-gauge shellcrackers, and produce a weaker "bang". The Ruggieri pistol and "Capa" cartridges offer an improved range of approximately 300 m (Briot and Eudot 1994; Ball 1997). "Bangers" and "whistlers" effectively deterred black-crowned night-herons and great blue herons from predating fish at a fish hatchery (Andelt et al. 1997).

Pistol-based pyrotechnics can be very effective if they are used properly. If they are not used properly, then birds can easily habituate to them, and control is not attained. In landfill situations, where gulls are difficult to control, proper use of pyrotechnics has achieved control of gulls at the Tower Landfill near Denver (Davis and Davis 1994) but improper application has been unsuccessful at the Britannia Landfill near Toronto (Miller and Davis 1990a,b). Pyrotechnics are major components of most airport bird control programs in North America.

Screamer shells were found to be 100% effective at dispersing Canada Geese from urban parks even though broadcasts of alarm/distress calls were not (Aguilera et al. 1991). The use of screamer shells had some long-term effects on the goose distribution. After five days of using screamer shells, Aguilera et al. (1991) found an 88% reduction in the number of geese using a site during the following five days.

The rope-firecracker is a pyrotechnic device made of cotton rope with waterproof firecrackers attached (Littauer 1990a). The rope is lit at one end. It burns slowly from one end to the other, and intermittently ignites the next firecracker along the rope; each firecracker makes a loud noise when it detonates. Rope-firecrackers have been suggested for use in deterring birds from landfill sites, fish-farms and agricultural areas (Salmon and Conte 1981; Booth 1983; DeFusco and Nagy 1983). Firecrackers are useful for deterring birds from a small area for a short time.

Store-bought firecrackers (normally used for holiday celebrations), attached to a piece of wood and ignited, were reported to scare thousands of roosting blackbirds from a residential area. The firecrackers were deployed for three consecutive nights (Bliese 1959). Better and safer techniques are now available.

Rockets and Mortars

Rockets (e.g. marine signal rockets, skyrockets and star shells) are normally projected from a launching rod and make a hissing sound as they travel (Hussain 1990). Some rockets may explode (e.g. jupiter shell), producing a display of fireworks and a loud noise at the same time. Mortars would be used in the same way as other pyrotechnic devices to disperse birds (Koski and Richardson 1976). Rockets would be useful at night, but would not be useful during the day unless they also produced a loud bang. Mortars, on the other hand, would be useful during both day and night. The noise produced by a mortar is much louder than an exploder or shotgun, and thus would probably disperse birds from a larger area. Skilled operators may be required. There have been several accidents related to the use of mortars and many operators have abandoned use of them for safety reasons.

Evaluation. – Pyrotechnics undoubtedly are among the most used bird control devices on airports. Pyrotechnics can and do scare birds but, without effective presentation, birds commonly habituate to the loud bangs. Presentation is the critical factor. Because of their portability and flexibility of use, pyrotechnics that are fired from shotguns or pistols are the most effective type. Extremely effective bird control programs have been based primarily on the use of pyrotechnics. Contrastingly, bird control programs that have employed much larger numbers of pyrotechnic shells have been largely ineffective. A relatively small number of pyrotechnics, used at appropriate times and in appropriate circumstances with regard to the behaviour of the birds, can keep hundreds of birds away. The technique is labour intensive. One effective technique, used successfully on gulls at landfills, has been to use pyrotechnic shells to prevent birds from landing, rather than allowing them to land and then dispersing them. The best methods of presentation likely vary from species to species, and experimentation is required, but the general approach is to be selective in your shots. Do not fire too often. The more indiscriminately that pyrotechnics are used, the more quickly birds will habituate. Do not fire until the birds are close enough that the shot will explode very close to them. Do not waste shots at birds that are too far away. Properly used, pyrotechnics can train birds to avoid coming to a formerly attractive area.

FOD (foreign object damage) can be a concern with 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).

Advantages

1. Rockets and mortars are potentially effective over large areas.
2. Pyrotechnics are effective both during the day and at night.
3. Direction and intensity of firing can be controlled.
4. They can be used as complementary devices with other deterrents.

Disadvantages

1. Pyrotechnics cannot be used in situations where fire would be a hazard, e.g. near dry vegetation or fuel.
2. Shooting at birds may not be acceptable in some public places.
3. Shotgun- and pistol-launched shells are useful only over relatively small areas at any one time.
4. Use of pyrotechnics is labour-intensive.
5. Birds can habituate to pyrotechnics if they are used improperly.
6. Pyrotechnics may be difficult or impossible to deploy in some situations.
7. Pyrotechnics can pose hazards to operators and bystanders if not used carefully.

Recommendation. – Recommended, if used selectively and sparingly as discussed above. Shotgun- and pistol-launched shells are the most adaptable types of pyrotechnics.

Literature Reviewed.-Andelt et al. 1997; Aguilera et al. 1991; Anderson 1986; BSCE 1988; Bartelt 1987; Beck 1968; Bliese 1959; Bomford and O'Brien 1990; Booth 1983; Briot and Eudot 1994; Burger 1983; Coniff 1991; Cummings et al. 1986; Davidson 1968; DeFusco and Nagy 1983; Davis and Davis 1994; DeHaven 1971; Draulans 1987; EIFAC 1988; Elgy 1972; Faulkner 1963; Feare 1974; Fellows and Paton 1988; Fitzwater 1978; Geist 1975; Green 1973; Grun 1978; Handegard 1988; Kevan 1992; Koski and Richardson 1976; Kress 1983; LGL Ltd. 1987; Littauer 1990a,b; Lucid and Slack 1980; Mattingly 1976; Miller and Davis 1990a,b; Mott 1980; NCC 1989; Nelson 1970; Nelson 1990a; Nomsen 1989; Noriss and Wilson 1988; Parsons et al. 1990; Radford 1987; Salmon and Conte 1981; Salmon et al. 1986; Southern and Southern 1984; Taylor and Kirby 1990; USDA 1991; U.S. Dep. Interior 1978.

Gas Cannons and "Exploders"

Description. – Gas cannons or "exploders" are mechanical devices that produce loud, banging noises to frighten birds. The "bangs" are produced by igniting gas (acetylene or propane). The noise of the explosion resembles or is louder than that of a 12-gauge shotgun (Feare 1974; 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 photo cell 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.

Biological Basis. – The sudden, loud bang from a gas cannon is capable, at least initially, of scaring birds away from an area. This flight response probably is related to the similarity of the bang to that of a shotgun shot (for those species that have been hunted), and to a 'startle' reflex reaction. However, without reinforcement that this bang represents a potential threat to the birds, birds soon habituate to these sounds.

Literature. – Gas cannons can be effective at dispersing birds 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. Sometimes it is necessary to elevate the cannons if foliage or equipment interfere with the sound of the blast (U.S. Dep. Inter. 1978; Hussain 1990). Birds habituate to the sound of the explosions, particularly if no other techniques are used to reinforce the threat of the cannon (DeFusco and Nagy 1983; BSCE 1988). Rotary mounts, variable firing intervals, and use of other complementary deterrent methods are helpful in delaying habituation. Gas cannons, in combination with other dispersal methods such as pyrotechnics, have been found to reduce numbers of gulls visiting landfills (e.g. Risley and Blokpoel 1984; Miller and Davis 1990a,b).

For dispersing gulls at airports, one cannon for every 50 m of runway has been reported to be effective (DeFusco and Nagy 1983). (It is not advisable to position gas cannons near runways, given the risk of aircraft striking these propane-fueled explosive devices.) However, cannons have also been found ineffective for long-term bird dispersal programs at many airports because of habituation (BSCE 1988). Cannons may be most helpful where only short-term deterrence is needed. Sugden (1976) indicated that cannons are among the most useful methods for reducing waterfowl damage to grain crops. Propane cannons were very successful at frightening cormorants at shipyards (Martin and Martin 1984) and can be valuable in reducing blackbird damage on cornfields (Dolbeer et al. 1979). For dispersing blackbirds, one cannon for every 4-10 ha works well (LGL Ltd. 1987). Setting cannons to fire at 30 s intervals can disperse blackbirds and Starlings from roosting areas (U.S. Dep. Interior 1978).

Gas cannons have proven to be effective deterrents for areas up to 4 ha in the cases of nongame species (Salmon et al. 1986), 18-24 ha for dabbling ducks in grain fields (Stephen 1960, 1961), and 50 ha for scaup on small lakes (Ward 1978). In the study by Ward (1978), the cannons were used in combination with scarecrows and lights.

Interviews. – A common complaint made by people that we spoke with regarding gas cannon systems is the limited period of their effectiveness. Birds habituate to the sound of the cannons within a relatively short period of time – a matter of days in some cases. Gulls at the Nottawasaga and Wasaga Beach landfill sites came to ignore the bangs of propane cannons there. In fact, observations were made of gulls perching atop the cannons, lifting off the units with the 'click' noise that preceded the explosion, then immediately settling back down atop the cannons (Steen Klint, Environmental Services Department, County of Simcoe, Ontario, pers. comm. 1998). Gulls regularly stood on the ground within 2-3 m of the units. Mark Adam (Falcon Environmental Services, Inc.) commented that (1) these units are very loud and this can be a serious problem where you have to control birds near residential areas (noise complaints); (2) the automated timer could lead to the scaring of birds at an inappropriate time, such as into the path of an aircraft taking off/landing. There is an indication that repetitive use of cannons may actually attract gulls to landfills (R.A. Davis, LGL Limited, pers. obs.).

At the Calgary International Airport, birds also have been found to habituate to the sounds of the cannons. However, cannons are still employed on an as needed basis and do scare birds away at least for short periods (Brian Richmond, Calgary Airport Authority, pers. comm. 1998). Bird control staff there have found that shorter periods between shots keeps the birds more on edge and thus more easily dispersed. Brian Richmond added that maintenance of the cannon units is an ongoing problem and while the best effect is achieved by moving the units around, they are not easy to move.

Dave Ball (Vancouver International Airport, pers. comm.) mentioned that they have positioned gas cannons at problem sites on the airfield, such as puddles where birds gather, and directly fire the cannon with a remote control device when needed. In this case, the cannons are being used like pyrotechnics.

Evaluation. – As with pyrotechnics, the efficacy of gas cannons varies with the method of presentation. Birds quickly habituate to gas cannons that fire at regular intervals and are not moved. Within a relatively short period of time the cannons become completely ineffective. Variation in the frequency of firing, number of shots per firing sequence, direction of firing, and location of the cannon on the airfield will prolong the period of effectiveness. Two or three shots in rapid succession, with variable firing intervals and rotation after each shot, is one good technique. The greatest control and variability can be achieved with remote firing of the cannon under the direction of the bird controller. Birds likely will habituate eventually, however, unless other supplementary techniques (including occasional killing) are employed.

Advantages

1. Direction, timing and volume of the blasts can be controlled.
2. Gas cannons are movable.
3. They are automatically operated and require checking only once a day.
4. They are effective day and night.

Disadvantages

1. Birds can rapidly habituate to the sound of the blasts.
2. Cannons must be supplemented with other deterrent devices.
3. Older gas cannons should not be used in areas where fire would be a problem.
4. Compared to the size of an airfield, the effective area is relatively small.
5. Regular maintenance is required.

Recommendation. – Cannons should not be relied upon as the sole or even the major component of a bird control program. Cannons are recommended for occasional use as part of an integrated airfield bird control program, in conjunction with other products and techniques. Cannons must not be deployed near fuel because the igniter for the cannon could ignite the vapour.

Literature Reviewed. – Bomford and O'Brien 1990; Booth 1983; Bradley 1981; BSCE 1988; Conover 1984; DeFusco and Nagy 1983; Devenport 1990; Dolbeer et al. 1979; Feare 1974; Hussain 1990; LGL Ltd. 1987; Littauer 1990a; Martin and Martin 1984; Miller and Davis 1990a,b; Mott 1978; Naggiar 1974; Nelson 1990a; Payson and Vance 1984; Risley and Blokpoel 1984; Salmon and Conte 1981; Salmon et al. 1986; Sharp 1978; Stephen 1960, 1961; Stickley and Andrews 1989; Sugden 1976; Truman 1961; U.S. Dep. Interior 1978; Ward 1978.

Agri-SX

Description. – Two bird control products marketed by the Agri-SX company of Quebec - the "Rotating Hunter" and the "Falcon Imitator" - are discussed here. Each product combines visual (hunter or falcon images) and auditory (propane cannons) stimuli to deter birds. These units are relatively new to Canada, although they apparently have been in use in Europe for several decades.

The "Rotating Hunter" consists of two propane cannons, and the metal silhouette of a person with a gun, on a rotating base atop a tripod. The entire system is taller than a person. The two cannons fire alternately in opposite directions, and the guns and "hunter" swivel with the force of each shot and with the wind. The frequency of the shots and on/off periods of each unit can be controlled with a mechanical timer. Agri-SX claims that the "Rotating Hunter" protects 20 ha of open land.

The noise stimulus of the "Falcon Imitator" also is provided by a propane cannon. The propane cannon pulse propels a "plunger" which pushes a fringed rubber disk up an 8 m pole (supported by a tripod). The plunger drops back quickly while the disk parachutes back down more slowly. This "lure" is said to imitate a falcon chasing a bird. As with the "Rotating Hunter", the timing and on/off periods can be controlled. The "Falcon Imitator" is said to be effective within a 150 m radius; the "birds never get accustomed to the falcon imitator" according to the manufacturer's promotional material.

Biological Basis. – The loud bang of a propane cannon is known to be effective at scaring birds for short periods of time (see discussion of gas cannons above), but birds soon habituate to the noise. Scarecrows, like the hunter image, also have short-term effectiveness. On a biological basis, it would appear that birds would habituate to these Agri-SX products relatively quickly although perhaps less rapidly than to a gas cannon alone because of the visual stimuli of the hunter and falcon images.

Literature. – There are no published or unpublished independent studies of these Agri-SX units. However, see the discussion about gas cannons above, and "Visual Deterrents - Scarecrows, Flags, and Streamers" later in this section.

Interviews. – The company's promotional literature lists more than 20 locations where the "Rotating Hunter" and "Falcon Imitator" have been used to control birds. These include agricultural, industrial, and airport settings. Personnel at several of these sites were contacted for information.

Overall, opinions of the efficacy of these products ranged from very satisfied to "no better than a propane cannon". No one considered these products to be the magic answer to all their bird control problems but rather a part of a multi-faceted program. None of the locations contacted employed the Agri-SX products on their own; they were used along with other control products and techniques. No comprehensive, rigorous test of the "Rotating Hunter" and "Falcon Imitator" is available. Consequently, the following review comments must be regarded as anecdotal.

One of the most heavily promoted endorsements of the Agri-SX products in the company literature is the removal of a nesting colony of gulls at the Daishowa pulp and paper plant at Quebec City. We spoke with Marcel Barriere of Daishowa, Inc.. A colony of mostly ring-billed gulls had grown to approximately 25,000 pairs by 1992 or 1993. During 1993 and 1994, there was a large-scale egg removal program at the colony, conducted by the Canadian Wildlife Service. Gull numbers declined subsequently to about 15,000 pairs. In 1995, one Agri-SX "hunter" and two "falcon" units were installed. In conjunction with the use of pyrotechnics, gulls were eliminated from the site in 1995.

The Agri-SX system has been used each year since at the Daishowa site and there still are no gulls. Each year the Agri-SX equipment has had to be used less often to scare the gulls away. Apparently the gulls have moved to an existing "natural" colony site on an island away from the Quebec City area. Concurrent with the gull control program at Daishowa, the municipality of Quebec City implemented a widespread program to reduce the number of food sources for the gulls. Regulations were enacted to prohibit the feeding of gulls by the public; household garbage had to be enclosed in hard containers rather than plastic bags that the gulls could tear. Apparently there was a marked reduction in the number of gulls throughout the entire Quebec City area.

Because of the coincidental use of other control products (pyrotechnics) and methods (egg collecting, regional garbage control), the elimination of nesting gulls at the Daishowa site cannot be attributed solely to the Agri-SX products. It also is impossible to measure the relative contribution of the Agri-SX systems to the overall result.

The "Rotating Hunter" and "Falcon Imitator" also have been used at sanitary landfill sites. We spoke with Steen Klint (Environmental Services Department, County of Simcoe) about the efficacy of these units at the Nottawasaga and Wasaga Beach (Ontario) landfills, and with Larry Conrad about his experiences at the Britannia Landfill (Mississauga, Ontario). Again, in both cases, the units were used in conjunction with other products and techniques. These included pyrotechnics, overhead lines, habitat management, and occasional killing. Klint and Conrad each considered the "Falcon Imitator" to be more effective than the "Rotating Hunter". Neither felt that they could rely on these products alone to control birds at these sites, but the units did scare gulls away. It is not known how long these units were in place and thus if there was the opportunity to investigate habituation to the devices by the gulls.

Mark Adam of Falcon Environmental Services, Inc., a bird control company, has familiarity with the "Rotating Hunter" and "Falcon Imitator" at landfill and industrial facilities. He did not find these products to be any more effective than propane cannons without the "hunter" or "falcon" features. In his experience, other propane cannons on the market have more sophisticated and reliable electronic timing mechanisms. The Agri-SX units employ older mechanical timers that are less accurate and less dependable. Adam also felt that the design of the "Falcon Imitator" was ill-suited to Canadian winters. Snow, ice, and freezing rain would impede the movement of the "falcon" up and down the 8 m pole. Overall, he considers regular propane cannons to be as effective and significantly less expensive, than the Agri-SX products. Nevertheless, he suggested that these units could be part of a broader bird control program.

In March 1998, 12 "Rotating Hunters" and 6 "Falcon Imitators" were installed at the Jean Lesage Airport in Quebec City. This is the first implementation of the Agri-SX products at a major Canadian airport. Pyrotechnics will be used as well. The results of this program may provide a more comprehensive evaluation of the efficacy of these units.

Evaluation. – At present the jury is still out on the Agri-SX products, and will be until rigorous and independent tests are conducted. The results of the installation at Jean Lesage Airport hopefully will be instructive. (No controlled studies are being conducted there, unfortunately.) These Agri-SX products probably are quite similar to gas cannons as bird deterrents. Although habituation may occur more slowly than with gas cannons alone, habituation is still a considerable concern given the need for long term effectiveness at airports. It is likely that "Rotating Hunters" and "Falcon Imitators" will suffer from the same limitations, and be used best in the same manner, as gas cannons.

Recommendation. – Given the considerable cost of these units, their similarity to the less expensive gas cannons, the more sophisticated timing devices available on gas cannons, and the lack of adequate testing, a major purchase is not recommended. Testing of one or a few units may be considered if the bird control program is not reliant on these.

Literature Reviewed. – Only company promotional literature.

Bird Gard AVA and Bird Gard ABC

These products broadcast electronically-synthesized (Bird Gard AVA), or electronicallyreproduced (Bird Gard ABC), alarm and distress calls of a short list of pest bird species. See "Distress and Alarm Calls" below for a discussion of this method of bird control.

Av-Alarm

Description. – Av-Alarm is a commercially-available electronic sound-producing device that broadcasts synthetic sounds in the 1500 to 5000 Hz frequency range at sound levels of 118 dB at one metre. To be effective, Av-Alarm sounds should be selected to match natural frequencies of alarm and distress calls of the species of concern, or to match the frequencies of intra-flock communications. Sounds are projected through speakers that each cover an angle of 120?. The timing and frequency of broadcasts can be controlled by interval timers and photocells. The unit can be powered either by a 12-volt battery or by 110/220-volt 50-60 Hz A.C.

Biological Basis. – Given that the sounds produced by Av-Alarm units are synthetic, there would appear to be no biological bases for the sounds to repel birds. However, the sudden onset and/or loud volume of the sounds may startle birds into departing an area on occasion. Birds also may avoid some novel sounds initially.

Literature. – Av-Alarm has been used primarily in the agricultural industry to deter birds from food crops. Most evaluations of its success have been subjective. However, Av-Alarm has been tested as a method of deterring waterfowl from agricultural and coastal areas, and at airports.

Av-Alarms appear to have been used successfully to reduce numbers of small birds feeding on various crops (see Koski and Richardson 1976 and DeFusco and Nagy 1983 for reviews). Preliminary tests from a more recent study suggest that Av-Alarm was an effective method of reducing damage to grapes that was caused by European starlings, cape sparrows and masked weavers (Jarvis 1985). Although most tests of Av-Alarm have been on landbirds in agricultural areas, some reports suggest that Av-Alarm can also be useful in reducing numbers of gulls and plovers at airports (BSCE 1988).

Av-Alarm units appear to have some deterrent effect by themselves, but may be more useful in combination with other scaring methods. For example, Av-Alarm had some deterrent effect on Starlings feeding on blueberries, but the addition of shotguns, gas cannons or decoy traps sometimes appeared to result in less depredation (Nelson 1970). Martin (1980) used an integrated system consisting of Av-Alarm, a propane cannon, and other manually deployed devices to reduce numbers of birds that used a waste-water holding pond, but he did not attempt to isolate the value of the deterrent devices separately. Likewise, Potvin et al. (1978) found that an Av- Alarm and propane cannon in combination were more effective in deterring landbirds from corn fields in Quebec than was either of these devices by itself.

Negative evaluations of Av-Alarms were provided by Booth (1983), who reported that Av- Alarms were not as effective as distress calls in repelling birds. LGL Ltd. (1987), Bomford and O'Brien (1990), and Devenport (1990) noted that birds habituate to the noise. Thompson et al. (1979) noted that the heart rate of Starlings increased only slightly when they were exposed to Av-Alarm whereas marked increases in heart rates occurred when birds were subjected to broadcasts of distress and alarm calls of starlings from both North America and Europe.

We are aware of only one rigorous study of the effectiveness of Av-Alarm as a deterrent device for waterfowl in agricultural situations. Canada Geese were successfully deterred from agricultural fields surrounding a wildlife refuge in Wisconsin (Heinrich and Craven 1990). During their experiments, control and experimental fields were interspersed and it is not known whether the device would have been as effective if there had not been nearby areas of suitable habitat without the deterrent device.

Wiseley (1974) studied the effect of a gas-compressor simulator on the distribution and behaviour of Snow Geese on the Yukon North Slope. This study provides an indication of how Snow Geese might react to noises that do not have a biological significance to them. The simulator caused geese to break from their normal flight formations, to flare, to call, to increase or decrease their speed of flight and to land. They avoided an area within 800 m of the simulator where the most intense sound was broadcast. Thus noise from an Av-Alarm or Phoenix or Marine Wailer may cause similar reactions by Snow Geese.

Crummet (no date; 1973) conducted two experiments suggesting that Av-Alarm might be an effective method of dispersing water-associated birds in aquatic situations. He did not, however, provide sufficient details to permit evaluation of changes in numbers of birds with respect to distance from the deterrent device before and during the experiment, or to assess the possibility that factors other than the Av-Alarm may have contributed to the observed changes in numbers.

Evaluation. – The Av-Alarm broadcasts synthetic sounds that are produced electronically, similar to the Phoenix Wailer but with a much smaller repertoire of sounds. Given the limitations of the Phoenix Wailer systems see above), the Av-Alarm is likely to be even less effective. The synthetic sounds broadcast by these systems do not have a biological basis and therefore are unlikely to be effective over the long time frames required at airports. There may be some limited use for Av-Alarms on airports where local, short term dispersal is required.

Advantages

1. Can be used to disperse birds in many types of habitats.
2. Av-Alarms may be effective at night.
3. Av-Alarm is not as species specific as some deterrent systems.
4. Av-Alarm does not require constant human attention, but changes in location and adjustments in the characteristics of the sounds will reduce the rate of habituation.

Disadvantages

1. Birds appear to quickly habituate to the sounds if Av-Alarm is used by itself.
2. Other devices may have to be used to make the Av-Alarms effective.
3. Personnel working near Av-Alarms should wear hearing protection devices.

Recommendation. – Not recommended as a long term bird deterrent, or as a critical component of an integrated bird control program. Phoenix Wailers probably are more effective given the larger repertoire of available sounds and greater flexibility of delivery. Av-Alarm may be more effective when used in combination with other devices such as pyrotechnics and gas cannons.

Literature Reviewed. – Bomford and O'Brien 1990; Booth 1983; BSCE 1988; Crummet n.d., 1973; DeFusco and Nagy 1983; Devenport 1990; Gunn 1973; Heinrich and Craven 1990; Jarvis 1985; Koski and Richardson 1976; LGL Ltd. 1987; Martin 1980; Nelson 1970; Potvin et al. 1978; Sharp 1978; Thompson et al. 1979; Wiseley 1974.

Distress and Alarm Calls

Description. – Distress and alarm calls are given by many species of birds when they are captured, restrained, injured, or otherwise in danger. The calls are species-specific, signal danger, and warn other members of the species to disperse. In some cases, distress calls of one species are recognized, and cause dispersal, by another species (Aubin and Brémond 1989; Aubin 1991). Commercial systems are available that broadcast taped distress calls. Many of these units are mobile; some can be mounted on vehicles (Elgy 1972; Currie and Tee 1978). Solar- and windpowered models now exist. In recent years, high quality digital recordings have become available as well.

Biological Basis. – The link between distress and alarm calls and escape responses is very strong because of its high survival value. It is the biological significance of the calls that makes them a powerful tool for bird dispersal. It takes more time for habituation to occur with distress and alarm calls (vs. artificial noises, for example) because of the biological relevance of these calls.

Literature. – Playbacks of recorded distress or alarm calls are used commonly in attempts to disperse birds from airports, agricultural and residential areas, aquaculture facilities, and some other locations. It is important to broadcast the sound at the most effective location and time in order to have the greatest possible deterrent effect. Thus, a mobile vehicle is desirable. In order to maximize effectiveness and minimize habituation, it is important that the sound be played sparingly and at times when the birds are likely to be most responsive (cf. Transport Canada 1986). This requires a human operator rather than an automatic timer. The effectiveness of this method also depends on the quality of sound that is broadcast; therefore, high quality equipment should be used (Brémond et al. 1968).

Playbacks of distress or alarm calls are widely used in dispersing gulls from airports, and occasionally from landfills and reservoirs (e.g. DeFusco and Nagy 1983; Payson and Vance 1984; Transport Canada 1986; BSCE 1988; Howard 1992). Playbacks have also been very successful in dispersing large flocks (up to 10,000) of European Starlings from roosting sites (Frings and Jumber 1954; Block 1966; Pearson et al. 1967; Feare 1974; G.F. Searing, LGL Limited, pers. comm. 1998). Keidar et al. (1975) found that distress calls deterred flocks of Skylarks and Calandra Larks from feeding on agricultural crops. Smith (1986) reported that birds were dispersed from airports by repeated broadcasts of distress calls. Spanier (1980) reported that juvenile and adult Black-crowned Night Herons could be deterred from commercial fish ponds by playing recordings of their distress calls. Playbacks of distress/alarm calls are most effective if they are begun before birds have established a routine or normal activity pattern in an area. They should also be applied before or as birds are entering an area rather than after they have arrived and settled there to feed or roost (Elgy 1972; Searing, pers. comm.).

Gulls emit an alarm/distress call when they have been captured or sense danger (Frings et al. 1955). When they hear an alarm call, gulls do not react in the same way as starlings. Gulls initially fly toward, and circle over, the source of the alarm call, apparently to investigate; then, they slowly fly away (Hardenberg 1965; Brough 1968; Stout et al. 1974). At airfields this behaviour can present problems if the gulls are attracted toward an active runway (Cooke-Smith 1965; Brough 1968) and care must be taken to avoid this situation. Gulls should be attracted away from a runway to distress calls and then moved further away with pyrotechnics.

Playback of distress or alarm calls is often most effective if used in conjunction with another deterrent method, e.g. firing of shellcrackers (Transport Canada 1986). Brough (1968) conducted 405 trials at five Royal Air Force (RAF) airfields over a one year period. Recorded distress calls were effective in dispersing gulls (including herring gulls) from the airfields. The distress calls were also used in conjunction with pyrotechnics. Brough found that the combination of distress calls and pyrotechnics was most effective, followed by distress calls alone, and then pyrotechnics alone. The combination of distress calls and pyrotechnics was later used by base firemen at RAF bases to disperse birds (Blokpoel 1976). Many other workers have found the distress call/pyrotechnics combination to be effective (Brough 1965, 1968; Busnel and Giban 1968; Bridgman 1969; Dahl 1984).

Mott and Timbrook (1988) found that distress/alarm calls are effective at dispersing Canada Geese from nuisance situations at campgrounds. Their call combination did not include a typical distress call; it included an alarm call of a lone goose and the calls made by a flock of geese as they flew away after being harassed. The calls alone resulted in a 71% reduction in the number of geese using the campgounds after five days of broadcasting calls. When supplemented with racket bombs, 96% of geese left. However, Aguilera et al. (1991) found that Canada Geese in parks reacted to the same alarm/distress calls by becoming alert and sometimes moving up to 100 m away from the source of the call, but the birds did not leave the area. The presence of nearby alternative habitat may determine the effectiveness in a particular situation.

Proper deployment of distress/alarm calls will increase their efficacy and reduce habituation. Habituation may occur if the call is played continuously (Langowski et al. 1969; de Jong 1970; Burger 1983). For example, Starlings habituated to distress calls played continuously but not to those played intermittently for intervals of 2-95 s. The U.S. Department of Interior (1978) recommended playing calls for 10-15 s each minute when Starlings and blackbirds are entering a roosting area. Block (1966) reported that broadcasting distress calls for 10 s per minute for 50 min successfully dispersed Starlings. To minimize the rate of habituation, the broadcast of distress/alarm calls should be repeated as soon as birds attempt to return after being dispersed (Slater 1980). This does not allow birds time to recover from the stimulus. Mott and Timbrook (1988) reported that Canada Geese did not habituate to playbacks of distress/alarm calls, but they mentioned that birds recognised the vehicle that broadcast the sounds and retreated before it began broadcasting. Thus the true stimulus for dispersal is ambiguous. In a five-year test in Holland, Hardenberg (1965) found little evidence of habituation by gulls to distress calls emitted by loudspeakers deployed along the edges of runways at an air force base. Brough (1968) found no habituation during a one-year test at five U.K. airfields.

Other factors may influence the effectiveness of distress/alarm calls. Species found in open habitats, such as prairie, field, tundra and marine habitats, may depend on visual cues, while species found in forested areas may rely on distress calls that they can hear (Boudreau 1972). Some species, like gulls, respond to alarm calls after they have visually confirmed that there is danger. Flocks usually react more strongly than individuals, and resting or loafing birds are more easily dispersed than feeding birds. Some species of birds such as the Oystercatcher and Wood Pigeon (European species) are reported not to emit distress calls (Bridgman 1976). Distress calls are sometimes effective over long distances (Aubin and Brémond 1989).

Interviews. – The distress call/pyrotechnic combination has been found effective on gulls at Calgary International Airport (Brian Richmond, Calgary Airport Authority, pers. comm., 1998). They find that the distress calls agitate the gulls and enhance the follow-up pyrotechnics. The digital recordings are preferred over cassette tapes at Calgary because of the clearer sound they produce.

Evaluation. – Alarm and distress calls have been known for over 30 years to be effective at dispersing some, but not all, species of birds. Because broadcast systems are mobile and versatile, distress/alarm calls can be very useful in airport situations. Alarm/distress calls also can be used to create agitation in birds, thus enhancing the dispersal effect of other techniques, such as pyrotechnics.

There are some limitations. The initial curiosity of most gulls toward such calls makes these calls a potential initial attractant rather than deterrent. Distress calls are not readily available for all species (e.g., some species of shorebirds; Gunn 1973), and some species do not have distress/alarm calls.

Broadcast devices are available that "detect" birds (by sound and radar) and broadcast distress/alarm calls only when birds are present, rather than on a pre-determined broadcast sequence. This delays the onset of habituation.

Advantages

1. Habituation to distress or alarm calls may be relatively slow if they are used sparingly and in conjunction with other complementary deterrent methods.
2. This technique can be used day or night.

Disadvantages

1. Many species of birds do not emit distress or alarm calls.
2. Distress and alarm calls have not been recorded for many species. Recordings of these calls would need to be obtained in order to be available for timely use.
3. Most distress/alarm calls are at least partially species specific. Broadcasting the call of one species may not disperse other birds.
4. Weather conditions may affect transmission of sound.
5. Playback of distress or alarm calls is not likely to be useful unless the timing of the playbacks is controlled by an on-site operator. Thus, the method is labour-intensive.

Recommendation. – Highly recommended. The use of distress and alarm calls is considered to be an essential component of an airport bird control program. As with all bird control systems, proper presentation by trained bird control staff will significantly enhance the effectiveness of these calls. See the discussion of effective use of distress/alarm calls above.

Literature Reviewed. – Aguilera et al. 1991; Aubin 1991; Aubin and Brémond 1989; Beklova et al. 1981, 1982; Block 1966; Boudreau 1968, 1972; Brémond 1980; Brémond and Aubin 1989, 1990, 1992; Brémond et al. 1968; Bridgman 1976; BSCE 1988; Burger 1983; Currie and Tee 1978; DeFusco and Nagy 1983; de Jong 1970; Elgy 1972; Fay 1988; Feare 1974; Fitzwater 1970; Frings and Frings 1967; Frings and Jumber 1954; Frings et al. 1955, 1958; Gunn 1973; Grun and Mattner 1978; Howard 1992; Inglis et al. 1982; Keidar et al. 1975; Kreithen and Quine 1979; Kress 1983; Langowski et al. 1969; Littauer 1990a; Morgan and Howse 1974; Mott and Timbrook 1988; Naef-Daenzer 1983; Payson and Vance 1984; Pearson et al. 1967; Rohwer 1976; Salmon and Conte 1981; Schmidt and Johnson 1983; Slater 1980; Smith 1986; Spanier 1980; Transport Canada 1986; U.S. Dep. Interior 1978.

Calls of Predators

Description. – Most predator sounds could be broadcast using the same equipment as distress or alarm calls. Predators of birds include other birds (such as hawks or falcons), certain mammals, and humans (Gunn 1973; Thompson et al. 1968).

Biological Basis – The playback of the call of a predator signals that a predator is nearby, and birds may react to this with heightened awareness and perhaps flight. In natural situations, predators usually hunt silently so that they do not "announce" their presence. Thus, the playback of predator calls would seem to be an unnatural presentation of a stimulus.

Literature. – Broadcasts of the protest calls of the Sparrow Hawk successfully repelled House Sparrows, and habituation was not observed after 6 days of exposure to the sounds (Frings and Frings 1967). The playback of a Peregrine Falcon call was effective at dispersing gulls from Vancouver International Airport (Gunn 1973; LGL Ltd. 1987).

Although predator sounds can have a startling effect on birds, they can also attract birds in some situations. For example, crows and blackbirds will mob or attack Great Horned Owls, particularly when they have newly-fledged young. This reaction also occurs around nests or rookeries of gulls and terns.

Evaluation. – It is difficult to evaluate the efficacy of broadcast predator calls for dispersing/deterring birds. The biological basis is unclear, and although studies to date have been positive, there have been few of them. More research needs to be conducted on many aspects of predator sounds and responses by pest birds.

Recommendation. – Predator calls show sufficient promise that they are worth testing. However, predator calls should not be a critical component of any airport bird control program until proven effective.

Literature Reviewed. – Frings and Frings 1967; Thompson et al. 1968; Gunn 1973; LGL Ltd. 1987.

High Intensity Sound

Description. – High intensity sounds can be produced by sonic booms, blasting using explosives, horns, and air-raid sirens.

Biological Basis. – Very high intensity sound could produce distress, pain, or discomfort; thereby causing birds to leave an area where the noises occurred. Secondarily, at greater distances, the sounds could cause startle reactions that scared the birds but did not cause discomfort.

Literature. – Thiessen et al. (1957) conducted preliminary tests using an air-raid siren to disperse ducks from ponds. They found that repeated broadcasts of intense sound caused some birds to vacate the pond after two or three days. Their methods and sound level measurements were not clearly explained. Holthuijzen et al. (1990) reported that a number of Prairie Falcons flew away from their nests after blasting from explosives occurred. The sound levels of the blasts, measured at the entrances of two aeries, averaged 136 and 139 dB, respectively. However, the falcons returned to their nests within minutes. Bell (1971) reported that the reactions of birds to sonic booms varied considerably. Most species reacted by flying away, running or crowding together.

Although not a sophisticated device, a bicycle horn that was inserted into an agitator of a washing machine produced an "ear-splitting" noise that dispersed roosting blackbirds from a residential area (Bliese 1959).

Evaluation. – High intensity sounds produce variable responses when birds are exposed to them. Most high intensity sounds cannot be reproduced easily, nor are they immediately effective in repelling birds. A horn attached to a boat or vehicle may be useful as a supplementary device in lagoons and marshes, and smaller water bodies. However, to produce sound levels high enough to repel birds at a practical distance would require extremely high intensities near the sound source. Because high intensity sounds can cause hearing damage and other human health effects (Fuller et al. 1950; Frings 1964; Wright 1969; Kryter 1985), this technique impractical at most airports.

Recommendation. – Not recommended.

Literature Reviewed. – Bell 1971; Bliese 1959; Davis 1967; Ellis et al. 1991; Fringes 1964; Fuller et al. 1950; Holthuijzen et al. 1990; Kryter 1985; Thiessen et al. 1957; Wright 1969.

Ultrasonics

Description. – Ultrasound is normally defined as sound at frequencies too high to be detected by humans. The upper limit of human hearing is generally taken to be 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. In many situations, other types of noise-based deterrents (e.g., propane cannons) are annoying to humans.

Biological Basis. – Suppliers of ultrasound-emitting devices have for many years claimed that their devices can deter birds. However, most species of birds do not hear ultrasound (Fay 1988; Hamershock 1992). Therefore, ultrasound is not an effective deterrent.

Literature. – Even though some birds can detect sounds up to or slightly above 20,000 Hz, they do not appear to be affected by broadcasts of ultrasound, probably because they do not use ultrasonic communication. Woronecki (1988) found that pigeons did not exhibit a fright response when exposed to ultrasound. Also, there was no evidence of a reduction in the number of pigeons nest-building or egg-laying when the nesting area was ensonified with ultrasound. Beuter and Weiss (1986) found no evidence that gulls either heard or reacted to ultrasounds. Griffiths (1988) reported that a combined sonic-ultrasonic bird repelling device did not affect several species of birds (e.g. chickadees and jays). Based on the known frequency ranges for hearing by the above species, it is unlikely that any of them could hear ultrasound.

Previous reviewers have concluded that ultrasonic methods are ineffective in scaring birds (e.g. Koski and Richardson 1976; DeFusco and Nagy 1983; Bomford and O'Brien 1990). Likewise Hamershock (1992), based on an extensive review, found that ultrasound did not reduce bird numbers by more than 5%, if at all. Ultrasound has also been found ineffective in repelling rodents (Lund 1984; Bomford and O'Brien 1990), but showed some promise in repelling bats, many of which have good hearing at ultrasonic frequencies (Martin 1980; Fay 1988).

Evaluation. – Ultrasound is not effective as a bird deterrent device.

Recommendation. – Not recommended.

Literature Reviewed. – Beuter and Weiss 1986; Bomford and O'Brien 1990; BSCE 1988; DeFusco and Nagy 1983; Erickson and Marsh 1992; Fay 1988; Frings and Frings 1967; Griffiths 1988; Hamershock 1992; Koski and Richardson 1976; Lund 1984; Martin 1980; Truman 1961; Woronecki 1988.

Aircraft Engine Noise and Infrasound

Research has recently been undertaken to investigate the potential for (1) the controlled generation of certain discrete noise frequencies of aircraft engines or other aircraft parts, and (2) low frequency sound (infrasound) to disperse birds (Short et al. 1996). No results of this research are available yet. For either technique to be successful, not only would birds have to be able to detect these signals they also would have to associate the signals with danger sufficient to make them depart an area. Habituation to these signals also would have to be considered.