Reducing the density of breeding gulls influences the pattern of recruitment of immature Atlantic puffins Fratercula arctica to a breeding colony

Abstract

1. By acting as both competitors and predators, gulls (Larus spp.) are generally considered to reduce significantly the attractiveness of potential breeding sites for other birds. This perceived threat posed by gulls to other breeding birds has led to the implementation of gull control procedures at many seabird colonies. However, the extent to which reducing gull numbers benefits other species has received little rigorous scientific investigation. 2. During a gull control programme (1972-89), gull nest density on the Isle of May, south-east Scotland, was reduced by between 30% and 100% in different sections of the island. Following termination of the original programme in 1989, several sections were maintained as gull-free by repeated removal of nests. 3. We used data collected over a 23-year period to determine the extent to which the spatial variation in puffin Fratercula arctica recruitment was influenced by changes in the density and spatial distribution of breeding gulls resulting from the control programme. 4. The presence of breeding gulls significantly affected the pattern of recruitment of puffins to the colony. Puffin recruitment rate was highest in the sections of the island where gull nest density was low. Gull density explained 21% of the variation in puffin recruitment rate. 5. These results suggest that the reduction in the number of breeding gulls substantially increased the attractiveness of areas of the colony as breeding sites for puffins, and is thus likely to have played an important role in the pattern of expansion of the puffin population on the island. 6. Synthesis and applications. Following a recent increase in the conservation status of both herring L. argentatus and lesser black-backed gulls L. fuscus , there has been a move to make management decisions more objective. This has highlighted the need for studies such as this, aimed at assessing the impact of gulls and their removal on other breeding birds, to ensure that any future control programmes are both necessary and effective.