Seasonal dispersal and mortality in the Silver Gull, Larus novae-hollandiae Stephens, and Crested tern, Sterna bergii Lichstein, in Australia

Abstract

Since 1950, 9064 young and 59 adult silver gulls, Larus novae-hollandiae Stephens, and 2814 young and 545 adult crested terns, Sterna bergii Lichtenstein, have been banded in the south-east and south-west of Australia. The numbers of significant recoveries (omitting dead chicks) were 163 (1.8 per cent.) young gulls, 42 (1.5 per cent.) young terns, and 7 (1.3 per cent.) adult terns. In eastern Australia, silver gulls dispersed mainly northward about 260 miles, extending to 800 miles, during the first winter; in the second year they were within 200 miles of the breeding-place. They first bred when 2 years old. In Western Australia they dispersed up to 100 miles south. Most recoveries were made during January-March, with a marked peak in March for birds taken on fishing-lines; least were made during August-November, the breeding season. Young and adult crested terns dispersed north and south from colonies in h-ew South Wales, mostly within 260 miles but some around 600 miles from their colony. Colour-banded adults nested 130 miles south of their location in the previous year, and others were 50-100 miles north of it during the breeding season. There was a slight increase in the numbers recovered during April-Xay. Dispersal and breeding habits in each case are correlated to the described regional subspecies, and seasonal mortality to feeding habits. The survival value of different dispersal patterns and constancy of breeding location may be related to generalized (silver gull) compared with specialized (crested tern) habits, especially feeding.