Methods for population control within a silver gull colony.

Abstract

Silver gulls can threaten the welfare of humans and other wildlife. Current superabundant gull numbers should be managed to reduce this risk. Denying gulls access to food at artificial sites, combined with direct population control, may reduce silver gull numbers in the long term. Control measures implemented at gull colonies overseas were trialled. Human disturbance in the colony associated with routine visits to study plots led to reduced nesting density. Egg-pricking reduced nesting success; it did not induce adults to incubate for extended periods even though gulls were recorded sitting on nonviable (although not pricked) eggs for up to 76 days. Removal of eggs from nests within experimental plots did not affect overall nesting success for these plots. Habitat modification, by mowing of long grass at the colony site prior to the commencement of breeding, decreased both the density of nests in mowed areas and nesting success. Selective culling of breeding adults from experimental plots was effective in reducing population size immediately and suppressed nesting by other individuals that attempted to breed later in the breeding season. The combination of habitat modification, culling and human disturbance reduced breeding success at colonies.