Some people view seagulls as nuisance birds, as they damage crops and threaten human safety. Seagulls are known to collide with aircraft more often than any other birds. They also have a tendency to build their nests on rooftops and swoop down to snatch food while people are eating outdoors. As they tend to scavenge from dumpsters, there is a risk of transmitting diseases to humans when they roost near water reservoirs.
Seagulls are considered migratory birds and hence are protected by federal laws. Many states in the United States also have laws to protect these birds. Hence, to take seagulls away from an area, professionals require a permit issued by the U.S. Fish and Wildlife Service. Bird-control professionals first have to use physical barriers and mechanical techniques to frighten away the birds. When these control methods fail, the permit is issued.
Courtesy of ehow.com