Measurements and observations (breeding success, territorial behaviour, morphometric measurements, blood hormone level, etc) of breeding pairs and non-breeding individual South Polar skuas at Northern Rookery, Cape Bird

South polar skuas (Catharacta maccormicki) are strongly territorial and the number of territorial pairs in any given area is relatively constant from year to year. The presence of adult non-breeding skuas in small groups near breeding pairs suggests that populations are limited by territorial behaviour. The size and composition of the non-breeding group was monitored at the Northern Rookery at Cape Bird. Individuals were trapped, banded and morphometric measurements and weight were taken. Daily surveys were made of the size and composition of the group and the position of all individuals was noted twice per day. Territorial behaviour and breeding success of pairs within the group was monitored throughout the season with nests visited at least once every 3 days recording data on laying chronology, cause of breeding failure, growth rates of young and reproductive success. Behaviour observation give insight into pair status, sex and dominance relationships of non-breeding birds. Blood samples were collected for steroid hormone level comparisons between breeding and non-breeding birds. Males and females from failed pairs were removed and held in captivity for 18 - 20 days to determine if there is competition for territories. The vacated territories were monitored for replacement rate by new birds. Once captive birds were released the time it took to re-possess their territories was monitored.