THE EFFECTS OF DISTURBANCE CAUSED BY BOATING ON SURVIVAL AND BEHAVIOROF VELVET SCOTER MELANITTA-FUSCA DUCKLINGS

We studied the consequences of human disturbance and gull predation on brood survival of velvet scoter Melanitta fusca in the Archipelago of South-West Finland in 1990 and 1991. Each brood was exposed to distur bance by boats on average 8.5 times a day in 1990 and 3.5 times a day in 1991. Disturbance lengthened the swimming distances of ducklings an d reduced the time used for feeding. Broods disturbed more frequently than average were smaller than those disturbed less frequently. At lea st 60% of ducklings died before the age of three weeks. The common pre dators of ducklings in the study area are the herring gull Larus argen tatus and the great black-backed gull Larus marinus. The daily predati on rate by gulls on velvet scoter ducklings was 4.7%, which means that 56% of ducklings are caught by gulls during the first three weeks. Th e frequency of gull attacks was 3.5 times higher in disturbed than in undisturbed situations.