The impact of mass outbreaks of black flies (Simuliidae) on the parental behaviour and breeding output of colonial common gulls (Larus canus).

Abstract

Studies in colonies of common gulls in Poland show that black fly outbreaks can affect breeding success in colonial waterbirds. During massive black fly outbreaks, many pairs of common gulls deserted their nests, both during the incubation period and after hatching. Remaining pairs exhibited less parental care, spent less time at territories and when present, often wheeled above their nests instead of incubating, brooding, or feeding their chicks. Increased absence of adults resulted in increased nest predation by crows and magpies and frequent starvation of broods. Mortality of chicks and adults caused by physical harassment and probably direct loss of blood and body fluids from biting flies was also observed. During black fly outbreak years, loss of clutches and broods increased by 40% to 60%. Low breeding success during outbreak years may limit recruitment of young birds to the colony resulting in long-term population decreases.