Breeding failure and feeding conditions of Lesser Black-backed Gulls Larus f. fuscus in the Gulf of Finland

Abstract

A ten-year study of the breeding success of Lesser Black-backed Gulls in a mixed colony in the Gulf of Finland revealed a high rate of parental failure in years of low rates of provisioning for the chicks . The parents ate their owneggs at the rate of 16% per annum (range 0-52%), and on average 13% of the chicks (range 0-25%) remained unfed. No such anomalies were detected among Herring Gulls in the same colony . Both gull species fed on the Baltic Herring, which occurred in 71 .8% of the regurgitations of Lesser Black-backed chicks . The chicks' begging behaviour was normal, and the need to guard the nest from local Herring Gulls was not observed to restrict the foraging opportunities of the Lesser Black-backed adults . The Lesser Black-backed parents were divided into three groups according to their chick-rearing result. The least effective group showed no response to the variation in the biomass of the spawning Herring stock in the Gulf of Finland. However, the occurrence of this group seemed to be connected with some unknown food-related factors . It is concluded that neglect of brood care is either arough reaction to variation in feeding conditions, or the symptom of unknown harmful physiological changes.