Sea Gull Biology and Information...

General Information:

The term gull refers to a group of 23 North American species belonging to the family Laridae. In the Great Lakes region, including Chicago and Milwaukee, the most common sea gull species is the ring-billed gull, which, along with the herring gull, is also one of the most widespread and abundant species across all of North America. The ring-billed gull population has been increasing steadily in recent history with the North American population estimated at 3-4 million. The breeding population in Chicago, discovered and estimated at less than 1000 individuals in 1975, has since grown to well over 100,000 individuals, and is continuing to increase at a rapid rate.

Appearance:

The ring-billed gull is a medium sized gull with a light gray back and upper wings, and white under parts and yellow legs. It’s most distinguishing characteristic is a distinct black band around a yellow bill. Ring-billed gulls are considered “three year birds” meaning they don’t attain the described adult plumage until their third year, going through various mottled brown plumages in the process.

Breeding:

Ring-billed gulls begin breeding at 3-4 years of age, and nesting occurs generally from mid April to late June in the Chicago and Milwaukee area. They are colonial nesters, meaning multiple pairs nest in close proximity to each other--many colonies contain thousands of nesting pairs! The average clutch size of a ring-billed gull pair is 3 eggs, and the lifespan of ring-billed gulls averages 10-15 years. Couple that with a low predation rate on adult birds, and high fidelity to colony sites, and that’s how local populations explode over short periods of time—it is estimated that some local Chicago colonies have increased over 400% in less than 10 years.

Migration:

Ring-billed gulls are considered a migratory species. In fact, there was no record of nesting ring-billed gulls in Illinois until the mid 1970s, until that point, they only used Chicago as a stopping point during migration. Gulls will migrate as far as they need to in order to find open water and food. For the Chicago and Milwaukee populations, between landfills, Lake Michigan, and man-made ponds, they may not have to venture too far to find either.

Feeding:

Gulls are very opportunistic and adaptive feeders and will forage on anything from chicken wings out of a garbage can, to invertebrates and fish, to chicks of other bird species or their own. This enables them to be successful in a wide variety of conditions.

Conflicts:

The rapidly expanding ring-billed gull population has led to many conflicts between seagulls and people. Rooftop colonies, common in Milwaukee are becoming larger and more widespread as time goes on and the population increases. In Illinois, the first rooftop colony was documented in 2001 and is continuing to be a growing, spreading, problem. Some of the issues include damage to the roof due to clogged drains from the build-up of nesting materials, feathers, and droppings—1 study demonstrated that the lifespan of a roof can be cut by 50% due to concentrated bird use. Another problem identified with rooftop nesting is aggressive, mobbing action of defensive sea gulls, this can often prevent HVAC technicians from completing necessary work. In addition, the build-up of droppings near ventilation systems has lead to concerns for the health of employees working inside the buildings. Sea gulls frequenting beaches also cause concern due to the large amount of e. coli present in their droppings. The build-up of sea gull droppings, and the associated e. coli, on the beach and in the water often leads to swim bans and beach closings. 1 study found that swim bans due to e. coli counts cost the City of Chicago over 2 million dollars! E. coli in Lake Michigan waters has been conclusively linked to gull droppings through numerous studies using DNA fingerprinting. Sea gulls can also pose a threat to other bird species by predating on chicks and eggs of other nesting sea birds. Lastly, sea gulls are involved in more aircraft collisions than any other bird species. These can certainly be serious and even fatal due to the size and flocking nature of sea gulls. All of these conflicts between people and sea gulls will increase, as the population continues grow exponentially, unless some measures are taken to stabilize this growth.

For more information on managing conflicts with gulls and migratory birds:
Servicing Illinois & Indiana: Wild Goose Chase, Inc., email or call 708.448.8878
Wildlife Management Consutling: Wild Goose Chase, Inc., email or call 708.448.8878
Servicing Wisconsin: Migratory Bird Management, Inc., email or call 262.790-BIRD