Salmonella carriage by herring gulls in the Clyde area of Scotland in relation to their feeding ecology.
Faecal examination of 2985 Larus argentatus captured at refuse tips in the Clyde area yielded Salmonella of 23 serotypes from 9.2% of birds during the breeding season and 9.8% outside the breeding season. The commonest serotypes were S. virchow and S. typhimurium. The infection rate in gulls was strongly correlated with that in the human population of the area. A higher infection rate in female than in male gulls outside the breeding season was associated with a greater use of refuse tips by female gulls. A further 163 L. argentatus from a breeding colony on Horse Island in the Firth of Clyde had a Salmonella infection rate of over 30%; birds from this colony frequented sewage outfalls and followed boats which dumped sewage sludge. There was no evidence of clinical disease due to Salmonella in the gulls.