Reproductive performance of the nominate Lesser Black-backed Gull under the pressure of Herring Gull predation

Abstract

Predation by Herring Gulls Larus argentatus was one of the major causes of death among Lesser Black-back chicks Larusf fuscus during a 14-year study period in the Gulf of Finland. Prior to culling operations, 17% of chick deaths were attributed to predation by neighbouring Herring Gulls in the study colony (chicks' rings were found in predators' food remnants). Culling these proven predators (2 pairs) lowered the predation rate to 2% and improved the fledging result significantly. However, predatory gulls from adjacent colonies, operating also in the study colony, were harder to track and remove. This "long-distance" predation still continued to operate even though the numbers of occupied Herring Gull nests in the entire Söderskär archipelago were reduced by 40% in four years (by egg culling) . Hence, random culling is not an effective solution in cases when selective removal of every specialized predator is not possible . This report does not, however, aim to asses the ethical grounds and the legitimacy of culling programs . Despite being a relatively large gull with a relatively large territory size, the nominate race of the Lesser Black-backed Gull shows behavioural analogies to the smaller, inoffensive gulls. It shows no intraspecific predation, and lacks effective defence against interspecific predation by larger gulls. Therefore the nominate fuscus seems to be especially vulnerable to Herring Gull predation. At present, the predation has an adverse effect on the reproduction of the nominate fuscus as it applies predominantly to the best-growing chicks, the potential recruits of the population .