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.

Increase 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. Installing overhead line grids or placing lines in a grid-like fashion over the water surface may also discourage gull use.

Resources: (online)

Gull Control