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General Note: |
Prepared for Chicago Department of Environment. |
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Summary: The regional population of ring-billed gulls (Larus delawarensis) has increased exponentially in recent decades. The high number of gulls in public areas leads to a variety of conflicts including general nuisance, property damage, economic losses, threatening human safety, and potentially threatening human health. For example, some studies have suggested a link between gull fecal droppings and elevated E. coli levels, which cause swim bans. The objectives of the Chicago Ring-Billed Gull Damage Management Project were to reduce the local production of ring-billed gulls, to reduce the severity of conflicts with gulls including swim bans, and to evaluate if the majority of gulls on Chicago lakefront are from local colonies. The Chicago Department of Environment, with support from the Chicago Park District, requested that USDA-APHIS-Wildlife Services provide assistance for the second consecutive year to implement this project. In 2007, we oiled 53 % of the estimated number of nests at two local colonies and found oiling the eggs with food-grade corn oil to be a successful method of preventing gull production. In 2008, we increased our gull population management efforts and oiled 80% of the nests in the two Chicago nest colonies, totaling 57,590 gull eggs in 22,136 nests. Without this project, we estimate that the Chicago hatch year gull population would have increased by an additional 22,000 to 44,000 gulls beginning in July 2008, based on a fledge rate of 1 to 2 birds per nest. We observed significantly fewer gulls on most of Chicago's beaches compared to 2007, which we believe is attributable mostly to our oiling efforts. The reduction in the number of gulls using Chicago beaches likely contributed to a reduction in conflicts, including a 35% decrease in the frequency of swim bans and advisories on Chicago's beaches (without canine harassment) in comparison to 2006. To observe gull movements in the region, 5,968 gulls in Chicago and 5,617 gulls in Northwest Indiana were marked and observed throughout the summer. We did not note any movement of marked after hatch year gulls between Chicago colonies. In addition, after hatch year gulls nesting in Chicago and East Chicago, Indiana tended to use beaches nearest to their nest colony. Recognizing this and the fact that gull use of beaches remained relatively stable throughout the swim season, it appears that gulls nesting outside of Chicago are not moving into the City in significant numbers to use beaches during the swim season. Thus, gulls nesting and being reared outside the City are not likely to make a significant contribution to the conflicts on Chicago's beaches during the swim season. |