Date of this Version
Prepared for Chicago Park District December 17, 2014
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.
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 2014, 96,643 ring-billed gull nests were rendered inviable. It is estimated that between 77,314 and 183,621 hatch-year ring-billed gulls have been prevented since the initiation of this project.
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 85%, with eight of the nine analyzed beaches showing 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. Conflicts with landowners and land managers have been reduced as a result of our efforts to limit production of young gulls.
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 eight 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 2014 swim season the proportion of tests resulting in a swim advisory compared to 2006 (baseline year) declined at 15 of 18 beaches tested.