FOOD AND FEEDING OF ANTARCTIC SKUA-CHICKS CATHARACTA-ANTARCTICA-LONNBERGI AND C-MACCORMICKI

In the austral summers 1993/94 and 1994/95, 54 chicks of C. antarctica lonnbergi, C. maccormicki, as well as mixed pairs of both forms, were ligatured in order to get quantitative results of food composition an d consumption. In total, 2992 g food was obtained from Brown Skua chic ks, 730 g from South Polar Skua chicks, and 214 g from mixed pair chic ks. The food composition varied between the forms. For the two years i nvestigated, there was no diet variation in the South Polar Skua and t he mixed pairs. Brown Skua chicks received 80 % penguin components, in cluding digested krill from penguin stomachs, and 12 % station garbage . Three percent were of marine origin. South Polar Skua chicks, in con trast, received 83-87 % fish, 3-13 % crustaceans, including krill, and no garbage. Mixed pair chicks got 73-80 % fish and 17-20 % penguin me at. The amount of food found in the ligatures differed for the three t ypes of samples, being on average 9.5 g per control in the South Polar Skua, 11.9 g in the mixed pairs and 26.0 g in the Brown Skua. The max imum mass obtained in one control bout was 119 g in a Brown Skua chick . The average rates at which food was found in the ligature samples we re 2.8 times per day for the South Polar Skua, 3.4 times per day for t he Brown Skua and 1.3 times per day for the mixed pairs. There were ne ither diel differences in the number of feedings nor in the amount of food delivered. With increasing age, the chicks were fed higher amount s of food per feeding, but no correlation between chick age and number of feedings was found. The number of feedings per day, the amount of food per feeding and per day did not differ between twins of eight Bro wn Skua pairs. For the Brown Skua, no preference of certain internal o rgans of the penguin body as a food source was found.