A COMPARISON OF HERRING GULL LARUS-ARGENTATUS AND LESSER BLACK-BACKEDGULL LARUS-FUSCUS NEST SITES - THEIR CHARACTERISTICS AND RELATIONSHIPS WITH BREEDING SUCCESS

Nest sites used by Herring Gulls and Lesser Black-backed Gulls in a mi xed colony were compared. Correlations between features surrounding a nest and breeding success at different stages of the breeding cycle ar e presented. Lesser Black-backed Gulls nested on more vegetated and fl atter areas than did Herring Gulls, even though the latter species had a lower hatching success at less vegetated sites. The difference in t he general topography of nest sites between the species suggests that the Lesser Black-backed Gull, through an individual defence strategy, may be better adapted to use sites which are accessible to ground pred ators than the Herring Gull. The fledging success of Lesser Black-back ed Gulls tended to increase with an increased proportion of relatively tall vegetation close to the nest. The Lesser Black-backed Gull may t herefore be able to leave its young unattended and rely on their conce alment for protection against predators. In contrast, the Herring Gull may rely more on parental vigilance to protect young. More frequent a ttendance by adult Herring Gulls at the nest site during chick rearing compared with lesser Black-backed Gulls supports this hypothesis.