Damage Prevention and Control Methods

Representative gull, family Laridae, subfamily Larinae.

Exclusion

Exclusion of gulls from attractive areas (garbage dumps, sewage discharge areas, drive-in theaters, catering establishments) near airports can significantly reduce gull use of airport surfaces and flight ways used by aircraft.

Exclude gulls from limited resting areas such as window ledges and roof tops by covering the surfaces with porcupine wires (see Pigeons). Exclude them from large areas such as water reservoirs, crop fields, and landfills, by installing wire or plastic netting or suspending parallel steel wire (28-gauge [0.36 mm]) or nylon monofilament line (50-pound [23-kg] test) over the area. Wire or monofilament spacing may be 40 feet (12 m) for large gulls to 15 feet (4.5 m) for smaller ones.

Birds have long been excluded from ponds in which fish are raised by using heavy, easily visible wires. Amling (1980) used strong, fine steel wires (28 gauge [0.036 cm]) on long, parallel spans up to 80 feet (25 m) apart to exclude gulls from a water reservoir. Wires have been used successfully to exclude most herring and ring-billed gulls from garbage dumps. McLaren et al. (1984) found that a wire spacing of 30 feet (9 m) worked if the food attraction was not too great. Fifteen-foot (6-m) spacing worked even with very abundant food. Blokpoel and Tessier (1984) reported the successful exclusion of ring-billed gulls from food service areas in Toronto using widely spaced nylon monofilament lines. They used more closely spaced lines to exclude the same species from part of a nesting area used by more than 70,000 pairs of gulls.

The reason that gulls rarely fly under or between fine parallel wires is not clearly understood. Other birds, including pigeons, regularly fly under and between the wires. The fine wires and lines are almost invisible at 35 feet (10 m) or more and may not be easily seen by gulls as they spiral down to land. The avoidance reaction when the wires are seen is spectacular and may disturb other gulls enough to make them avoid the wired area.

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Cultural Methods

Habitat modification to discourage gull use of areas includes reducing or eliminating food, nesting and resting sites, and water. Reducing food availability is not easy, because of gulls’ adaptability in using a wide variety of foods. Human food wastes, fruit and vegetable crops, insects, earthworms, and other invertebrates and vertebrates are all potential foods that may require careful control to reduce their availability. Municipalities may find it useful to modify or eliminate artificial feeding sites that gulls have habituated to in recent years, such as garbage dumps and landfills, fish docks, trawlers, food processing plants, sewer outfalls, and livestock feedlots.

Manipulate grass height by limiting mowing to discourage gulls from using airports, park areas, and playing fields as resting or loafing areas. A height of 8 inches (20 cm) may discourage laughing gulls, but herring gulls can see over it and will not necessarily be discouraged unless the grass is higher. Where ponds are attractive to gulls, filling or draining may aid in reducing the suitability of such habitats.

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Frightening

Frightening devices used successfully against gulls include shotgun shells, shell crackers, gas-powered exploders, and broadcasts of distress and alarm calls (see Bird Dispersal Techniques). In addition, gulls can be harassed by trained birds of prey or radio-controlled small aircraft, which can be constructed to resemble falcons. To be successful, all scaring devices should be used by experienced, dedicated personnel. Continuity and care in use are the most important factors. Most distress and alarm calls are species-specific and may even be specific to local dialects. They must be used sparingly to avoid familiarity and are best used from a stationary source. The birds will first approach the source of sound and after 5 to 10 minutes will move away from the area. Shell crackers can be used to direct the departure. They are most effective when the birds are airborne and have begun to move away from the sound source. Frightening devices are not a cure for repeated presence of gulls. Dead gulls or gull decoys placed in dead gull postures can be used, especially in conjunction with other frightening devices to frighten gulls from an area.

Avitrol^® concentrate (4-aminopyri-dine) is federally registered for the control of herring gulls in the United States. The current label allows for its use to frighten gulls that are feeding, nesting, loafing, or roosting near or in the vicinity of sanitary landfills, air-ports, and structures. Apply the concentrate to bread, as specified on the product label. Mortality is minimized by limiting the amount of bait offered. Avitrol^® used for this purpose is a Restricted Use Pesticide. State and federal permits are required in order to use Avitrol^® on gulls.

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Repellents

Polybutenes can be used as a tactile repellent to keep gulls from landing on beams, posts, and other structural materials. Methyl anthranilate is registered for use in shallow pools of water used for loafing and watering.

Toxicants

The toxicant DRC-1339 is a Restricted Use Pesticide that is registered in the United States for the control of nesting herring gulls, great black-backed gulls, and ring-billed gulls. Its use is limited to coastal areas where high gull populations are conflicting with less-abundant colonial water birds. The toxicant is mixed with bread and is placed directly on gull nests. DRC-1339 is slow acting and apparently painless. Death is caused by uremic poisoning.

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Trapping

Gulls can be live trapped by several techniques, including rocket or cannon netting over baited sites, setting box traps over nests and eggs, and spot-lighting at night and capturing with hand nets. Gulls are very mobile and if relocated, would likely home back to their original place of capture. Therefore, live-trapped gulls should be euthanized with carbon dioxide gas.

Shooting

Shooting gulls with shotguns or rifles can be a highly selective and useful form of control under certain conditions. Federal and possibly state permits are required. Shooting has been used to eliminate gulls that habitually fly over airport runways (for example, Kennedy Airport, New York) and of-fending individuals that are preying on the eggs and nestlings of protected species (for example, black-headed gulls, Norfolk, United Kingdom). Caution must be used so that shooting does not disturb the protected species. Shooting is not a very successful method for reducing large colonies because of the relatively small number of gulls that normally can be shot.

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Other Methods

Removal of nests, eggs, and young.

To be effective, removal of all nests, eggs, and young from a colony should be done every 2 weeks. Activities are time-consuming and labor intensive and renesting is usually attempted, often in more remote areas. Permits are necessary.

Sterilization of eggs.

Several methods can be used to ensure that eggs do not hatch, including pricking, formalin injection, shaking, and spraying with or dipping in an oil emulsion solution. To inhibit replacement, eggs must be returned to the nest and not externally damaged.