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We determined the importance of three landfills to a population of nesting Herring Gulls (Larus urgent&us, 3,250 pairs) on Lake Erie, Ohio, from May-July 1992. Fish was the dominant food ofadults and chicks throughout the study. Occurrence ofgarbage in the diet of adults and chicks remained low through chick-rearing then increased after fledging. Presence of telemetered adults at their nest sites decreased from incubation through post-fledging, in contrast to their increased presence at landfills during the same periods. Overall, females visited landfills more frequently and stayed longer than males; however, use of landfills by both sexes was minimal (~4% of total time) during all periods. Overall, gulls spent 43% and 4% of their time daily at the nest site and landfills, respectively. We estimate ?80% of the time remaining was spent on Lake Erie, presumably to forage. The estimated daily mean number of adult Herring Gulls at the landfills increased from incubation (143) to chick-rearing (723) to post-fledging (1,912). We estimate that 5-7%, 12-19%, and 35-55% of the adult nesting population was present at landfills at least once during incubation, chick-rearing, and post-fledging, respectively. The population turnover rate of adult Herring Gulls at one landfill decreased 50% from incubation and chick-rearing to postfledging. Significantly more gulls at the landfills were observed on areas other than exposed refuse and were not actively foraging, suggesting that landfills are important to Herring Gulls for other reasons such as loafing or social interaction. We conclude that landfills are unimportant to nesting Herring Gulls when alternate, higher quality food (e.g., fish) is available. The increased use of landfills by Herring Gulls during post-fledging, however, suggests that gull activity at landfills located near airports could dramatically affect aircraft safety during this time of year.

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