TP 13029
Removing birds by poisoning, trapping, or shooting generally is effective over only the short term. Long term bird control, as discussed previously, requires addressing the reasons why birds are attracted to the airport or fly by the airport. Nevertheless, there are occasions when killing birds is required to address an immediate threat to aircraft safety. Shooting birds, in particular, also can be used effectively to enhance the efficacy of non-lethal control methods, such as pyrotechnics. Lethal control methods likely would not reduce populations of common pest species over the long term. They may reduce local populations of common species over the short term and on a local scale, or reduce the local numbers of uncommon/rare and less mobile problem species. Major gull problems on an airport, for example, are not going to be controlled by killing gulls unless the killing is on an unprecedented scale. See the Transport Canada Manual for a description and discussion of poisons - Rid-A-Bird perches, Ornitrol (Avitrol), and strychnine - used for bird control.
Description. – Trapping is one of the oldest methods used to control birds (Shake 1968). Birds can be live-trapped using mist-nets, cage traps, cannon-nets (Hardman 1974; Draulans 1987; Beg 1990), or large funnel-shaped lead-in traps. Pole-traps were once used on fish and game farms (Randall 1975). However, pole-traps are non-selective in catching and killing birds. They are useless as a method of saving birds lives and are illegal in many countries.
Biological Basis. – Birds are trapped and subsequently either released at a distance far enough from the airport that they are unlikely to return, or are killed. Appropriate attractants, placements, and trap designs are available for a wide variety of species.
Literature. – Successful deployment of traps depends on many factors - such as the total number of birds, availability of food outside of the trap, and the birds' behaviour (i.e. wariness of traps, Nelson 1990b). Shake (1968) found that attempts to trap red-winged blackbirds near corn fields were ineffective because the population of birds was high in comparison to the number of birds that physically could be trapped. However, Mott (1978) reported that a small population of green-backed herons was captured by mist nets at a fish farm and released 40 km from the capture site. The birds did not return. Trapping was effective at controlling pigeons that roosted on the roofs of buildings and in city parks (Truman 1961). Birds that are hazardous to aircraft, such as hawks and owls, are sometimes trapped at airports and released in areas of suitable habitat distant from the airport (e.g. Hughes 1967; Wernaart and McIlveen 1989). It is important to release the birds far enough away and in suitable habitat; otherwise, many of them are likely to return to the trapping area. Moving traps to new locations every two days will increase the number of birds caught. In agricultural situations it is recommended to place traps in an area before birds arrive.
Evaluation. – Catching and moving birds can be time consuming, depending on the species and situation. Building traps can be expensive, especially if large numbers are needed. Complex traps may require considerable manpower and time to set up and maintain. Trapping in general, whether to kill or to move birds, is a short-term solution to an immediate problem.
Recommendation. – Trapping may be useful in special circumstances, such as for raptors. However, it should be noted that removal of experienced resident raptors may lead to their replacement by naive birds that are not experienced with airports and aircraft.
Literature Reviewed. – Beg 1990; Clark 1976; Davidson 1968; Draulans 1987; Fitzwater 1978; Hardman 1974; Hussain 1990; Jarvis 1985; LGL Ltd. 1987; Lucid and Slack 1980; Mott 1978; Nelson 1970, 1990b; Randall 1975; Shake 1968; Truman 1961; Wernaart and McIlveen 1989.
Gulls are responsible for bird hazards to aircraft at and near many airports. Shooting of gulls on airports is of limited effectiveness as a long term deterrent. In the short term, some gulls are removed and others are frightened away, but the dispersed birds soon return or are replaced by other birds (Heighway 1970; Blokpoel 1976; Harrison 1986). Shooting of gulls, however, is a useful control technique when used to increase the effectiveness of other scaring techniques such as distress calls, pyrotechnics, and models (Cooke-Smith 1965; Mason 1980; Harrison 1986). Killing should be used sparingly, and usually is limited by a permit required from the Canadian Wildlife Service. The occasional killing of gulls is an integral part of many control programs at landfills and airfields.
Over 50,000 gulls were shot at John F. Kennedy International Airport between 1991 and 1997 to reduce strikes with aircraft. This was a unique situation in which a colony of several thousand laughing gulls became established in Jamaica Bay adjacent to the airport. The gulls regularly traversed the airfield on route to feeding areas. While the best solution would have been to remove the nesting colony, this was not done because of its location in a National Park. In this situation, shooting was effective at changing the bird's flight patterns to avoid the airfield. The number of aircraft striking laughing gulls declined by 61% in 1991 and 76-89% during 1992- 1997, compared to the mean number of 136 strikes during 1988-1990 (Dolbeer and Bucknall 1997). However, the numbers of birds killed would not be allowed on a routine basis.
Recommendation. – Selective shooting is recommended as a component of airport bird control programs.
Water cannons and sprinkler systems, using water or water with wetting agents (surfactants), are sometimes employed to control "pest" birds (Harke 1968; Smith 1970; Lustick 1976; Glahn et al. 1991). Water spray has been used as a lethal control method to prevent birds from roosting in urban and agricultural areas. Surfactants are sometimes added in order to penetrate feathers. Once the feathers are wet, the body temperature of birds drops and, if the weather is cold, they may die. Spear (1966) suggests that a sprinkler or water spray system is useful as a method of keeping birds away from waterways.
The surfactant PA-14 was used widely for the control of blackbird and starling roosts between 1974 and 1992. Over this period an estimated 38.2 million blackbirds and starlings were killed through the application of PA-14 (Dolbeer et al. 1997). PA-14 did solve local roost problems, but Dolbeer et al. (1997) found no evidence (using North American Breeding Bird Survey data) that PA-14 applications caused declines in regional breeding populations of these species.
Recommendation. – Water spray, with or without surfactants, is recommended as a lethal control method or to disperse roosts birds. Water spray could also be used for short term dispersal of loafing flocks but it would be easier to use pyrotechnics.