Abundance, diet and Salmonella contamination of gulls feeding at sewage outfalls

The abundance and activity of gulls at sewage outfalls in South Wales and s outhern England was studied between 1972 and 1999. In winter, the black-hea ded gull was the most abundant species, followed by herring, common and les ser black-backed gulls. The abundance of black-headed gulls and herring gul ls was significantly correlated with the volume of sewage discharged. Sewer s supported only a small portion of the gull populations present in both ar eas, and a higher proportion of juvenile birds were present than at other f eeding sites. Sewage comminution increased the numbers of black-headed gull s feeding, but infrequent intermittent discharge reduced them by over a hal f. Gulls selectively consumed waste foodstuffs from sewage and thus helped recycle some of its organic constituents. However, some individuals carried bacterial pathogens, and could thus have contaminated nearby bodies of fre shwater, or grassland, by washing and roosting there. Full sewage treatment , as planned for most of the discharges in both study areas is likely to pr ovide the most effective means of gull control. (C) 2000 Elsevier Science L td. ALI rights reserved.