EFFECTS OF WEATHER ON THE CYCLIC PATTERNS OF COLONY ATTENDANCE IN THECAPE PETREL DAPTION CAPENSE

Colony attendance of Cape petrels on Nelson Island, South Shetland Isl ands, Antarctica, fluctuated in a non-random pattern. In the pre-breed ing period a relatively weak cycle of about 6 days was observed. Low a ttendance was associated with brief periods of either SE wind or stron g wind, the effects of which lasted 2 days. During breeding, regular a ttendance cycles were approximately twice as long (8 days) as the aver age incubation shift (3.8 days), which may have resulted from synchron ization of unemployed birds not engaged in incubation. Breeding attend ance was lowered on 2 days after strong wind and on days with SE wind, but only wind speed showed a significant effect when both variables w ere considered. Post-breeding colony attendance showed a continuation of the rhythm established during breeding, but with the majority of bi rds participating. Correlations found between wind factors and colony attendance suggest that some weather characteristics, which themselves were not truly cyclic, could act to synchronize the endogenous rhythm s of individual birds. Seasonal changes of wind effects on colony atte ndance could be interpreted in terms of foraging behaviour, i.e. as a consequence of the feeding grounds in summer being not restricted by s ea ice to one particular direction from the colony.