FACTORS AFFECTING DAILY ACTIVITY BUDGETS OF SOUTH-GEORGIAN SHAGS DURING CHICK REARING AT BIRD ISLAND, SOUTH-GEORGIA

Radio telemetry was used to record daily activity budgets of 26 South Georgian Shags (Phalacrocorax georgianus) during the chick-rearing period at Bird Island, South Georgia. There was a significant sex difference in the timing of feeding, with the female making the first trip of the day in 93% of pairs (n = 15). On average, each shag made 2.3 trips/day and was absent for a total of 6.22 hr/day. The majority of time away from the colony was spent diving (86.7%), but long recovery periods on the surface between dives and time needed to travel to the seabed resulted in only 1.06 hr/day being potentially available for prey capture. Given that these activity data were collected during a season when feeding conditions were favorable, breeding shags at Bird Island appear to have little capacity to increase the time available for prey capture. We speculate that the population may be extremely sensitive to changes in food availability. Males spent more time flying and on the sea than did females. On average, birds with broods of two or three chicks spent more time diving (6.42 hr/day) than those with broods of one (4.74 hr/day) but there was no tendency for the amount of time spent diving to increase with chick age. Although South Georgian Shags exhibited the same sexually distinct foraging patterns as Antarctic Shags P. bransfieldensis at a colony on the Antarctic Peninsula, their activity budgets differed radically, with shags at Bird Island spending a much greater percentage of their time away diving (86.7% compared with 8.4%).