Ecology of the Long-tailed Skua, Stercorarius longicaudus, at Scoresby Sund, East Greenland. Part four: Breeding success and growth of young

Breeding success and growth of young of Long-tailed Skuas were investigated in Northeast Greenland at Kap Stewart in 1973 and 1974, at Ugleelv and Kærelv in 1975, and at Kærelv in 1979. Territorial pair density was positively correlated with the percentage snow-free area in June. In 1973, estimated mean egg production per territorial pair was 1.4, but no young hatched. Egg loss was due to predation by Arctic Foxes, Alopex lagopus. In 1974 no eggs were produced due to scarcity of food on the tundra. In 1975 and 1979, estimated mean egg production per territorial pair was 1.2 and 1.9, respectively, and young did hatch, but none of them fledged. In both these years two-thirds of overall egg and chick mortality was caused by Arctic Foxes. Survival time of clutches and young in the different breeding years was negatively correlated with the number of foxes per unit of snow-free area. High breeding success of Long-tailed Skuas in Northeast Greenland occurs only in years with moderate to high food availability, a relatively low number of foxes and early to rather early disappearance of snow cover. Chicks gained weight rapidly from the first day to 12 or 13 days after hatching, when fast growth of culmen and tarsus stopped, and growth of wing slowed down. During the first two weeks in 1975 first-hatched chicks were heavier than second-hatched chicks of the same age and single chicks were similar to first-hatched chicks. The two longest surviving chicks reached an age of 24 and 25 days, at which time they had not yet fledged. Chicks and parents showed a circadian rhythm with greatest activity during the day and a period of sleep during the night in which the sun does not set at this latitude. The female stayed closer to the young than the male, but the male provided food more frequently.