COLONY EFFECTS ON FLEDGING SUCCESS OF GREAT BLUE HERONS (ARDEA-HERODIAS) IN BRITISH-COLUMBIA

We present 6 years of data on the distribution and fledging success of 4,510 Great Blue Heron nests in 31 colonies on the Pacific Coast of B ritish Columbia. Heros nested as solitary pairs and in colonies of up to 387 pairs. Almost half of all herons nested in just three colonies. An average of 1.7 young herons fledged per nesting attempt. The proba bility of a pair failing to raise fledged young was over 2.5 times gre ater in small colonies than large colonies. However, the probability o f a nest having >3 fledglings was over 12 times greater in a small col ony, than in a large one. Fledging success was significantly and posit ively correlated with the number of years a colony had been in use. Co lony size was not a significant correlate of the number of fledglings a pair of herons could expect to raise over the 6 years of this study.