Population ecology of the South Polar skua at Cape Hallett: 1967-1969

A banding study of the South Polar Skua (Catharacta maccormicki) was conducted over three field seasons (1966/67, 1967/68 and 1968/69) at Cape Hallett. A swinging door type trap was constructed in order to catch and band adult skuas in the area, contributing to the international banding scheme at the time. A population census was conducted over the same three seasons. In th 1960/61 season Maher (1961) reported that there were 181 pairs of skuas nesting at Hallett but only 113 pairs were found in the 1966/67 season, 105 in the 1967/68 and 98 pairs in the 1968/69 season. From studies on band returns and breeding success (including causes of mortality) of Cape Hallett skuas, it appears that the major reason for this decline is a high rate of adult loss from the population rather than an abnormally low breeding success. Breeding success was monitoring over the three seasons and were 18% (1966/67), 26.9% (1967/68) and 17.2% (1968/69) for percent chicks raised to fledging from eggs laid. The number of eggs laid by nesting females was found to be 1.85 eggs/female for the 1967-69 seasons combined. The effects of differences in food utilization on breeding success and laying date was also studied.