Date of this Version
Chicago Park District (February 8, 2013)
The large ring-billed gull (Larus delawarensis) population in the City of Chicago has caused various conflicts including general nuisance, property damage, economic losses, and threats to human health and safety. Several studies have shown a relationship between ring-billed gulls and increased levels of fecal indicator bacteria (FIB) such as Escherichia coli (E. coli) in nearshore waters. Results of tests for E. coli have led to the issuance of swim advisories at Chicago beaches.
The objectives of the Chicago Ring-billed Gull Damage Management Project were to (1) reduce the local production of ring-billed gulls, (2) reduce the severity of conflicts with gulls including the issuance of swim advisories, and (3) evaluate how limiting the production of gulls affects gull use of Chicago’s beaches. We hypothesized that oiling the majority of ring-billed gull eggs will continue to reduce the number of hatchyear ring-billed gulls produced in Chicago, and that the decrease in the number of hatch-year ring-billed gulls will therefore reduce severity of conflicts with gulls, including swim advisories on Chicago’s beaches.
Since the beginning of the Chicago Ring-billed Gull Damage Management Project in 2007, USDA-WS established that oiling eggs with food-grade corn oil was a successful method in reducing gull production. Between 2007 and 2012, 84,745 ring-billed gull nests were rendered inviable. It is estimated that since the initiation of this project, between 67,796 and 161,015 hatch-year ring-billed gulls have been prevented.
Management of ring-billed gull nests has contributed to a significant reduction in hatch-year gull use of Chicago beaches. Since 2007, hatch-year gull use of beaches has declined by 94%, with 8 of 9 analyzed beaches observing a significant reduction. The combined observations of hatch-year and after hatch-year gull use of beaches illustrated a reduction in gulls compared to 2007 observation totals. Reduction in conflicts with landowners and land managers has been documented as a result of efforts to limit production of young.
The connection between ring-billed gulls and water quality is becoming more evident. It has been demonstrated that a relationship exists between gulls and the concentration of E. coli at beaches. During our six treatment years and the prior (pretreatment) year, the Chicago Park District has routinely sampled for E. coli as a FIB to assess water quality. During the 2012 swim season the proportion of tests resulting in a swim advisory compared to 2006 (baseline year) declined at 12 of 14 beaches.