There are two gull species typically identified as causing damage in Minnesota: the herring gull and ring-billed bull. Populations of both have increased dramatically in the past century due to their ability to adapt to, and thrive in the human environment. Increased food resources, such as human trash, handouts, and agriculture, have probably been a primary factor leading to these increases. In addition, the development of large, inland reservoirs has probably influenced these reproductive booms as well. While other gull species, such as laughing and great black-backed gulls, are also known to cause damage, they are less common in Minnesota. Damage is categorized into four areas: damage to property, agriculture, human health and safety, and harassment of people.
Issues concerning damage to property include the fouling of boat docks caused by the guano (droppings) of large numbers of loafing gulls. Rooftops are also favorite loafing areas, and have even been used as colonial nest sites. The accumulation of guano on rooftops can destroy polyurethane roofing materials. Boat and pool covers made of the same materials can also be damaged.
Damage to agricultural crops has been known to include crops such as blueberries and grapes. While this type of damage is not prevalent in Minnesota, gulls, being opportunists, will also take advantage of stored forage, such as corn silage and other small grains. Livestock feedlots can provide an abundant food source. Fecal materials subsequently contaminate the forage, rendering it unsuitable for consumption by livestock. Other types of damage to livestock operations include predation on domestic ducks, and the potential risk of the spread of various avian diseases, such as avian influenza and Newcastle disease.
Gulls are the primary contributor to the bird-aircraft strike dilemma, accounting for over half of all bird strikes. Airports are prime real estate, with wide open vistas in which gulls can safely loaf while on the lookout for predators, and with short grassy areas from which they can forage for insects. These areas are especially attractive if there is an additional food source nearby, such as a landfill, or a large body of water. Reservoirs can also attract large numbers of gulls, potentially elevating fecal coliform levels, thereby rendering the water unfit for human consumption.
Gulls are relentless in their search for an easy meal, and many have learned that people are a great source of food. Individuals who learn to connect people with food can become quite bold. As with most wildlife species, those individuals that have become habituated to people are those who most often cause trouble, usually leading to their demise. Therefore, IT IS ALWAYS BEST NOT TO FEED GULLS, whether it be directly, or indirectly through unsecured trash or exposed pet foods. Other forms of harassment include the defense of nesting colonies that have been established on rooftops, which can be quite offensive as parent birds will often swoop while defecating or vomiting on the intruder.