Relationships between Black-legged Kittiwake nest site characteristics andsusceptibility to predation by large gulls

We quantified the relationship between Black-legged Kittiwake (Rissa tridac tyla) nest-site characteristics and risk of predation by Great Black-backed (Larus marinas) and Herring (L. argentatus) Gulls at Gull Island, Newfound land, Canada, during 1998 and 1999. We monitored kittiwake nesting cliffs t o identify nest sites attacked by large gulls and compared characteristics of attacked and successful nests among four study plots. We also examined w hich nest sites were attacked by Herring or Great Black-backed Gulls during calm (less than or equal to 10 km hr(-1)) or windy conditions (> 10 km hr( -1)). We found that kittiwake nests on plots with fewer nests were more lik ely to be attacked by gulls and less likely to fledge young. Nest density a nd nest location relative to the cliffs' upper edges significantly affected the risk of gull predation. Breeding success was correlated with nest dens ity and ledge width and differed significantly, among plots. Regardless of wind conditions both gull species were more likely to attack nests located on upper sections of cliffs than nests on lower sections. However, during c alm conditions, nest sites located on narrow ledges were less likely to be attacked by Great Black-backed Gulls. Our results demonstrate that for kitt iwake colonies where predation is an important source of breeding failure, the size of subcolonies and nest density affect the survival of kittiwake o ffspring.