Chemical Repellents

Chemical aversion agents have been used to control birds around commercial and residential areas (Fitzwater 1988; Woronecki et al. 1990), in agricultural situations (Clark 1976; Conover 1984; Knittle et al. 1988), at airports (DeFusco and Nagy 1983; BSCE 1988) and, less commonly, at sanitary landfill sites (Caldara 1970; White and Weintraub 1983; Woronecki et al. 1989). Birds tend not to habituate to chemical repellents.

Tactile Repellents

Description. – Most tactile repellents are sticky substances that deter birds from sitting on perches, such as building ledges, antennas, and airfield lights and signs. The chemical paste can be applied with a caulking gun, putty knife, spray can, or small tube. Recently, natural plant products also have been tested in this regard (Clark 1997).

Biological Basis. – The sticky materials do not trap birds, but repel birds presumably because of the tacky "feel". The biological basis for this avoidance behaviour is unclear. Plant compounds that have been tested caused agitation and hyperactivity in the birds. This reaction may be associated with the uptake, through dermal contact with the birds' feet, of chemicals in the plant compounds.

Literature. – No studies were found that reported on the efficacy of sticky tactile repellents. Clark (1997) reported that starlings became agitated and hyperactive after their feet were immersed in 5% oil extracts of the spices cumin, rosemary, and thyme. Starlings avoided perches treated with either R-limonene, S-limonene, ?-limonene, or methiocarb. These experimental results suggested that it may be possible to develop non-lethal, plant-based dermal repellents.

Mechanical means can be used also to repel birds from perching in unwanted situations. For example, a series of sharp objects, nails, wires etc. can prevent birds from landing on perches such as light fixtures, ledges, and poles. Some commercial products such as "Nixalite" are available for use.

Evaluation. – It is difficult to evaluate rigorously any of the sticky tactile repellents because there have been no quantitative efficacy reports. Sticky substances are laborious to apply and require that all perches be identified and treated, but do remain sticky for a year or more, depending upon climate. They are not effective at temperatures below about -9?C. These sticky materials are not aesthetically pleasing if that is a requirement, such as on certain building surfaces. Natural plant products show promise but have not been tested in the field yet.

Recommendation. – The chemical and mechanical tactile repellents can be used at airports but the resulting use, or lack of use, by birds should be properly documented.

Behavioural Repellents

Description. – Frightening agents and repellents such as Avitrol (4-aminopyridine) and Methiocarb (3,5-Dimethyl-4-(methylthio)phenyl methylcarbamate) are poisons that, in sublethal doses, may cause disorientation and erratic behaviour. They are usually added to bait. Typically only a portion of a bait presentation (e.g., 10% of corn kernels) is treated with the chemical so that only a small number of the birds to be dispersed are affected. When the treated bait is ingested, a distress response occurs (DeFusco and Nagy 1983; White and Weintraub 1983; Brooks and Hussain 1990). Distress calls from affected birds can start 15 min after ingestion, and can last up to 30 min after ingestion. Besides emitting distress calls, affected birds may become disoriented and exhibit erratic behaviour, often flopping about on the ground. This behaviour often alarms other birds, and causes them to fly away. If too high a dose is ingested, the bird will die. Tremors and convulsions occur before death if birds receive an overdose of the aversion agent, and these may induce other birds to leave the area.

Biological Basis. – There is a well-documented biological basis for the effectiveness of these chemicals, if used in the correct dosages. Unaffected members of a flock will disperse in response to the distress calls and stressed behaviour of flockmates.

Literature. – These agents have been used primarily on starlings, blackbirds and other passerine birds. However, Avitrol has also proven useful in dispersing gulls (e.g. Caldara 1970; Wooten et al. 1973; DeFusco and Nagy 1983; White and Weintraub 1983). The U.S. Air Force tested Avitrol at seven air bases and found it to be effective against gulls, starlings, crows, pigeons, and house sparrows (Seaman 1970). Avitrol also has been used successfully on loafing gulls at a naval air station in Norfolk, Virginia, on a crow roost at Friendship Airport near Baltimore, Maryland, and on pigeons at a hangar at Montreal International Airport (Blokpoel 1976). It has also been used successfully on gulls at landfills (Sweeney and McLaren 1987).

Avitrol is toxic and can be difficult to administer in a dose sufficient to cause the desired effect but not to kill the bird immediately. Death may be delayed and affected individuals may be able to fly away before dying elsewhere. This can lead to public relations problems.

Another problem with continued use of Avitrol as a control technique is the development of bait-shyness. Gulls will learn rapidly to identify and avoid the kinds of bait food (usually bread) that cause the unpleasant effects on their flock-mates. New baits can be substituted but there is a limited number of suitable bait types that can be used. Changing the bait also means that the appropriate amount of chemical to apply to the bait must be re-determined.

Evaluation. – Chemical aversion agents require attracting birds to an area and allowing them to feed in a pre-baiting and baiting sequence. This can create hazards in an airport situation. Thus, a more direct dispersal method is likely to have better results.

In situations where flocks of birds, especially feeding birds, do not immediately threaten air safety, it may be appropriate to use a chemical aversion agent. Feeding birds are particularly difficult to disperse from an abundant food source, and aversion agents may be useful in breaking the attraction to the food source. Supplementary dispersal methods would be needed, along with the aversion agent, in order to obtain maximum effectiveness. Effectiveness of baiting could be influenced by environmental conditions, number of birds, and bait preference. Birds have been shown to develop a conditioned aversion to some agents. Considerable care would be necessary in the use of potentially harmful agents like Avitrol and Methiocarb, and some mortality should be expected.

The direction of movement of dispersed birds is not controlled when using these behavioural repellents, and this could pose problems at airports.

Recommendation. – Chemical behavioural repellents, such as Avitrol and Methiocarb, are recommended for incorporation in an overall bird control program for parts of the airport where there are not direct bird hazards to operating aircraft. Realize, however, that these chemicals are for specific uses and should be applied carefully. Permits are required and the agent must be administered by a licenced Pest Control Officer.

Literature Reviewed. – Blokpoel 1976; Brooks and Hussain 1990; BSCE 1988; Caithness 1968; Caldara 1970; Clark 1976; Conover 1984, 1985a, 1989; Crocker and Perry 1990; Cummings et al. 1992; DeFusco and Nagy 1983; Devenport 1990; Fitzwater 1978, 1988; Green 1973; Knittle et al. 1988; Rogers 1978; Seaman 1970; Skira and Wapstra 1990; Sweeney and McLaren 1987; Truman 1961; Wakeley and Mitchell 1981; White and Weintraub 1983; Wooten et al. 1973; Woronecki et al. 1989, 1990.

Benomyl and Tersan

Description. – Benomyl and Tersan are commercial fungicides developed to treat fungal infections of turf. These (and other) chemicals also are effective at reducing earthworm populations. When sprayed along runway edges, earthworm populations there can be controlled. This addresses problems associated with birds, particularly gulls, attracted to airfields to feed on the worms in short grass areas. Benomyl has low toxicity to birds. Because earthworm control is a non-registered use for Benomyl, permits for this purpose have been difficult to obtain recently (Demarchi and Searing 1997). The future status of this restriction should be determined before planning to apply Benomyl or Tersan. Terraclor is another horticultural fungicide manufactured for seed and soil treatments at planting, and which also has been used to reduce earthworm densities (Demarchi and Searing 1997).

Biological Basis. – Benomyl, Tersan, and Terraclor reduce bird populations at airfields by reducing the population of earthworms, a food source. They are most applicable to the control of gull and plover numbers on an airfield during warmer months.

Literature. – Application of Benomyl at the Windsor International Airport reduced earthworm populations on treated runway verges (Tomlin and Spencer 1976). Similarly, Terraclor significantly reduced earthworm densities on treated plots at Vancouver International Airport (Demarchi and Searing 1997). No literature was reviewed regarding the efficacy of Tersan.

Allan and Cordrey (1992) tested two lumbricides on an airfield in the U.K. – one containing gamma HCH plus thiophanate-methyl, and another containing carbaryl. However, they recommended that the use of these chemicals be restricted to small-scale and occasional applications, and that any birds feeding on dead or dying invertebrates be dispersed. The concern is to reduce the pesticide intake of the birds and the pesticide loading of the environment.

Evaluation. – These earthworm control products apparently are effective at reducing earthworm populations, and therefore address this reason for birds (gulls primarily) to be attracted to the short grass areas adjacent to runways. They do not appear to be in widespread use at airports; perhaps because of environmental concerns.

Recommendation. – Occasional use of Benomyl and Tersan, and other tested and approved products that have been shown to control earthworm populations, is recommended for use where earthworms are creating major bird hazards near runways. This use would only be necessary at some airports.

Literature Reviewed. – Demarchi and Searing 1997; Larose 1996; Tomlin 1981; Tomlin and Spencer 1976.

Methyl Anthranilate - ReJeX-iT

Description. – ReJeX-iT is the trade name for a commercial bird aversion agent based on a naturally-occurring plant compound, methyl anthranilate. ReJeX-iT works as a non-toxic taste aversion agent because its taste is unpleasant to birds. ReJeX-iT is available in liquid and powder forms that permit application by spreader, sprayer, or fogger. It can be mixed in bait or in water. A bead formulation also has been tested (Cummings et al. 1998). Methyl anthranilate may be more widely applicable than previously available chemicals, which are difficult to use because of their toxicity. Ortho-aminoacetophenone, a non-toxic chemical similar to methyl anthranilate, also appears to have potential for repelling or dispersing birds at low concentrations (Mason et al. 1991).

Biological Basis. – Methyl anthranilate is a known taste aversive for birds. Many birds avoid eating Concord grapes because they do not like the taste of the methyl anthranilate that the grapes naturally contain. Although known biologically to be effective, the efficacy of ReJeX-iT as a bird aversive agent has been shown to depend to a large degree on its formulation, concentration, and the practicalities of application.

Literature. – A number of studies using captive and free-ranging birds have been conducted and published. These include laboratory studies, and studies at sanitary landfill sites and airports, studies of the aversive effects on birds feeding on fruit, grain and turf, and birds using standing water. Species studied include Canada geese, gulls, starlings, and woodpeckers among other species. The results of these studies show that ReJeX-iT can be effective at deterring birds in certain situations but the formulations used in some studies were not effective.

Both dimethyl and methyl anthranilate were strongly avoided by captive mallards and Canada geese when birds were offered both treated and untreated grain (Cummings et al. 1992). When offered only treated grain both ducks and geese reduced their food intake, but the mallards, and to a lesser degree the Canada geese, gradually increased consumption during the 2-4 days of the experiment. Cummings et al. (1992) assumed that the birds were habituating to the chemical, but they were not given an alternative food source, and the increased consumption may have been caused by increased hunger.

The methyl anthranilate formulations tested by Belant et al. (1995) repelled captive mallards in pen tests and free-ranging ring-billed and herring gulls from pools of water in field trials. However, in another test, Belant et al. (1996) found that the concentrations they used were not effective as a grazing repellent for Canada geese. Similarly, Cummings et al. (1995) also found that the particular formulation they tested showed limited effectiveness to reduce captive goose activity on treated grass plots, but showed promise given further refinements of the formulation. Belant et al. (1996) did show that there was no learned avoidance by pre-exposed geese. Problems with the application of ReJeX-iT precluded effective testing of its ability to repel birds from ponds at airports (Dolbeer et al. 1993). However, the results were promising; bird numbers did decrease at treated ponds post-treatment vs. pre-treatment.

Tests at landfill sites have shown positive and negative results. Vogt et al. (1994) reported that gull numbers were reduced at each of three landfills during periods of treatment with ReJeXiT. However, it was unclear to what extent the reduction in numbers was related directly to the taste-aversion effects of ReJeX-iT. The action of the spray used to apply the ReJeX-iT also caused gulls to move away, and pyrotechnics, wires and flags were used in conjunction with the ReJeX-iT at one site. In another case, a sizable landfill nearby provided an alternate food source for the gulls. Contrary to these findings, gulls numbers did not decrease during the ReJeX-iT treatment period at a major landfill near Toronto (Davis et al. 1995). Although gulls rejected food items sprayed with ReJeX-iT, the gulls did not leave the landfill or the active face. The gulls simply continued foraging, looking for unsprayed food items. It became apparent that the effective application of ReJeX-iT was not feasible at this large landfill simply because the active tipping face was too busy. It was impossible to keep the exposed waste treated with ReJeX-iT without interrupting the flow of disposal trucks and bulldozers.

The repellent effects of ReJeX-iT mixed with the synthetic landfill cover ConCover were tested with captive ring-billed gulls and brown-headed cowbirds by Dolbeer et al. (1993). Both species were repelled by the ConCover/ReJeX-iT mix; a higher concentration of ReJeX-iT was required to repel the ring-billed gulls than the cowbirds.

Evaluation. – ReJeX-iT has potential for selective bird control at airports. It is a natural, low toxicity product and it has been shown to be effective in certain applications. However, concerns regarding formulations, concentrations, frequencies of applications, and the practicalities of application must be addressed. Cost also may be factor; ReJeX-iT can be costly if coverage of a large area is required.

Recommendation. – ReJeX-iT is recommended for selective test use on airfields. One should not assume that ReJeX-iT will immediately provide positive results. Experimentation with different formulations, application frequencies, and concentrations may be required and these should be carried out on a small scale before large-scale applications are attempted.

Literature Reviewed. – Avery 1992; Belant et al. 1995, 1996, 1997; Cummings et al. 1992, 1995, 1998; Davis et al. 1995; Dolbeer et al. 1992, 1993; Mason et al. 1991; Porter 1995; Sinclair and Campbell 1995; Vogt 1992; Vogt et al. 1994.

Other Taste Aversives

Several other food treatments have been tested for their effectiveness at repelling birds. Dpulegone and Mangone, a form of d-pulegone, are found naturally in certain plants. D-pulegone has been demonstrated to deter blackbirds, starlings, northern bobwhite, and domestic dogs from feeding (Mason et al. 1989; Mason 1990; Mastrota and Mench 1994; Avery et al. 1996; Mason and Primus 1996; and Wager-Page and Mason 1996 in Belant et al. 1997b). Belant et al. (1997b) conducted tests to compare the relative repellency of these chemicals on caged brown-headed cowbirds fed treated millet. They concluded that mangone is less effective than d-pulegone and would likely be ineffective as a repellent for seed treatment. However, they felt that d-pulegone deserved further testing.

Belant et al. (1997c) felt that the use of dolomitic hydrated lime warranted additional testing as a taste aversive following the results of their tests on cowbirds and Canada geese. Lime could be a lower-cost alternative to methyl anthranilate in their opinion. The results of tests of dolomitic lime, activated charcoal, Nutra-lite (a silica-based compound) and white quartz sand as taste aversives on cowbirds and Canada geese revealed that lime and charcoal showed potential (Belant et al. 1997d).

Evaluation. – The efficacy and applicability of these products for airport bird control are undetermined. More testing is required.

Recommendation. – Not recommended at this time.

Literature Reviewed. – Belant et al. 1997a, b, c, d.