Habitat management

Agricultural areas

Gulls are predominantly attracted to agricultural landscapes when they discover an abundant, easily obtainable source of food, such as grain. If the source of food is removed, or access to it is denied, they will leave in search of better fare. Good husbandry practices, such as cleaning up waste grain, are advisable. Covering stored forage out-of-doors with materials such as geo-textile fabric, to prevent access by gulls and other wildlife, is also recommended. Silage, can also be accessed when it is fed to cattle in open feed bunks in barnyard areas. Feeding only amounts that livestock will immediately consume will ensure that no leftovers will be available for marauding birds. Again, be sure that any waste grain is immediately removed from the ground in the feeding area. Research indicates that gulls can consume their entire required daily food intake in as little as 15 minutes. Therefore, one must be diligent and timely in these husbandry efforts. If given access to food, even for a short period of time, they may never leave as they will never get hungry enough to do so. However, preventing feeding for as little as 2 days may cause them to abandon the site entirely.

Landfills

To reduce the number of gulls feeding and loafing at landfill sites, the same principles of food deprivation will apply as for agricultural areas, only on a larger scale. Preventive measures to consider include completely covering all areas of the active face with a soil cover immediately after every addition of refuse. This can be a challenge to landfill operators due to the gull’s ability to gulp down its daily food requirements in 15 minutes! Therefore, diligence and timeliness is again required. Preventing access to the active face through exclusion methods, such as wire grids or tightly-woven plastic mesh is also an option. The proper use of wire grids is discussed under exclusion methods below. Lastly, limiting the size of the active face will minimize the area needing protection.

Other practices to make landfills more inhospitable can be pursued in addition to the removal of the food source. Landfills often provide the wide open vistas that gulls prefer for feeding and loafing in safety. Low-growing vegetation, such as short grasses, is preferred over taller, dense vegetation, which could conceal predators. Short grassy areas are also alternative feeding sites, as they harbor and provide easy access to insects, such as grasshoppers. If operators are diligent in covering the landfill, but leave this alternative food source, gulls may remain in spite of their efforts. Therefore, the planting of alternative, taller grasses, such as native warm-season prairie grass is suggested. Native wildflowers can also be included in the mix to increase aesthetic s and to provide a food source for various pollinators. Vegetation should remain at least 10” tall and be quite dense. All bare soil areas at the landfill site should also be seeded, as these areas can become favored loafing sites. To prevent the invasion of woody species that may compromise a landfill cap, mowing can be conducted once annually, preferably in the spring. Woody growth can also be controlled through spot herbicide applications. If the establishment of native grass is not an option, a reduction in the mowing of existing grassy areas may also be of benefit.

The removal of unnecessary water sources is also recommended when trying to eliminate gull habitat on a property. Gulls are attracted to water for a variety of reasons, depending on the size of the water body. Even puddles will provide needed drinking water. Grading can eliminate these smaller sources, while larger areas, such as swimming pools, and wastewater treatment and storm water runoff ponds, may require covering or wire grids (see exclusion methods below). These larger bodies of water provide safe nighttime roosting areas. Smaller ponds can be made less attractive to gulls by the establishment of tall vegetation on the banks. Wetland shrubs and/or tall grasses are recommended. In landfill operations, care should be taken to avoid creating depressions in borrow areas from which soil is excavated for covering refuse. When covering or eliminating a water source is not an option, the repellent Goose Chase, containing methyl anthranilate, can be used to discourage use by gulls. However, this repellent can only be used on non-fish bearing waters such as temporary pools of standing water associated with landfills, airports or decorative fountains, and should not be used in areas where surface runoff has the potential to contaminate lakes or streams.

It is important to note that the implementation of these measures to prevent access by gulls at all landfills may help to reverse the upward spiraling trend in populations of both ring-billed and herring gulls. While these species sometimes come in conflict with people, they also can have a detrimental effect on populations of other shorebird species through competition for nesting sites and predation. Lastly, it is essential that all landfills within close proximity to airports carefully consider these recommendations, due to the hazard of bird strikes to aircraft. As previously mentioned, gulls have a strong affinity to airports, oftentimes choosing those close to their food source as primary or alternative loafing areas.

Airports

As with landfills, airports also provide the wide open vistas that gulls prefer for loafing and feeding in safety. Therefore, many of the habitat modifications would be the same, such as maintaining all grassy areas in a dense vegetative cover at least 10” in height, and if possible, eliminating water bodies (refer to the paragraph above concerning habitat alterations at water sources). When choosing grass species, care should be taken to avoid varieties that are preferred as forage by geese, such as Kentucky bluegrass, and avoid fertilizing and watering to further discourage use. Studies indicate that high endophytic tall fescue varieties (cool-season, perennial , sod-forming grasses), such as Kentucky 31, are not favored by grazers and some insects, and are being tested at a number of airports to reduce the presence of birds and small mammals, such as cottontail rabbits. Endophtytes are fungi that live between the cells of the above ground portions of the plant, and form a symbiotic relationship in which both the plant and fungi benefit. The plant provides the fungi with shelter, nutrients and reproductive potential through its seed, while the plant benefits through protection offered by the fungus in the form of alkaloids, which are a natural deterrent to herbivores. The plant is also more disease and drought tolerant, due to this relationship. While studies have shown that geese and small mammals will avoid these fescues, they have also shown them to be palatable to grasshoppers. Therefore, if tall fescues are to be used as turf-grasses at airports, maintaining a height of at least 10” is necessary to prevent access to gulls desiring to feed on the insects, as they cannot see over or through the grass when looking for potential predators.

Other food sources, such as earthworms, will also entice gulls to airports. After heavy rains, earthworms come out of the soil to seek dry ground, often finding their way onto airport runways in such numbers that they not only attract large numbers of birds, but can also cause airplanes to slide during takeoff and landing. Currently there are no pesticides approved for use in controlling earthworms, but structural modifications can be made to eliminate this hazard, such as installing worm-proof slit gutters along runways (http://www.int-birdstrike.org/Warsaw_Papers/IBSC26%20WPAE6.pdf). Other habitat alterations that can reduce their numbers along runways include the removal of grass clippings during mowing. Clippings left on the ground after mowing eventually decompose, increasing soil fertility, thus providing better habitat. Removal of clippings will also eliminate cover for small rodents, which may attract birds of prey.