THE FLOCK-FEEDING SYSTEM OF THE ADULT BLACK-HEADED GULL (LARUS-RIDIBUNDUS) AND THE FOOD OF ITS NESTLINGS

This research project concerning the flock-feeding system of the adult Black-headed Gull and the food of its nestlings, was conducted in various habitats in South Moravia (Czech Republic). In fields without vegetation, 56 cases were observed with the average flock size being 13.3-15.3 individuals. In fields with little vegetation, 40 cases were observed and the average flock size was 7.0-15.8 individuals. In harvested fields there were 15 cases, with an average flock size of 6.6-19.6 individuals. Finally in aquatic habitats, there were a total of 95 observed cases, where the flock size was 74.6-202.2 individuals. It has been confirmed that the environment has greater influence on the flock size than the time of observation (April-June). In addition, the influence of the observation site and distance from the breeding colony was also recorded and analysed. A total of 175 food samples from 4 age categories was analysed. The most commonly hunted food were insects (f = 58.3 %), plant components (f = 24.57 %) and earthworms (f = 13.71 %). The analysis showed that, with increasing age, the gulls sought more earthworms and cherries and less insects.