Evolution annuelle des effectifs et des biomasses des oiseaux antarctiques

Abstract

An estimation is made of the population numbers of the Antarctic and sub-Antarctic birds, their biomasses and their food consumption at sea, and of their seasonal variations. The total populations of the 46 species represent a grand total of about 350 million birds and a biomass of ca 850,000 tons. Forty nine percent of this population and 36 % of this biomass are found in the sub-Antarctic zone, as against 51 % and 64 % respectively in the Antarctic zone. The penguins represent 52 % of the total bird population and 92 % of the total bird biomass. Some seasonal variations occur, the difference between maximum and minimum values not exceeding 20 % however. On the average, 80 % of the birds live offshore, as against 20 % on land. The daily energy requirements are estimated to be of c 112 X 109 kcal, and the daily energy demands of c 160 X 109 kcal. The monthly food consumption at sea is about 4.7 million tons, 61 % of which are crustaceans, 24 % squids and 14 % fish. Penguins are the major consumers. The amount of food consumed does not vary much from month to month, the monthly maximum being only 70 % higher than the monthly minimum in the Antartic zone, and 56 % in the sub-Antarctic zone. Some hypotheses are formulated concerning competition for food between birds, seals and whales. There was probably no competition when whales were numerous in Southern Oceans, feeding on the huge summer planctonic production, little being left for birds and seals. The present situation is quite different, most of the summer production of plancton no longer being used on a large scale by mammals and birds.