BIOLOGY OF THE SOOTY SHEARWATER PUFFINUS GRISEUS

Abstract

On a small half‐acre island at the southern end of New Zealand a study was made of a complete community of Sooty Shearwaters from the end of 1940 to the beginning of 1957. In the season 1953–54, when the greatest emphasis was put on an estimate of the population, 551 marked birds were known to have been alive. This indicated a population of around 600 adult birds. Up to the end of January or a little later, unemployed birds constituted some two‐thirds of the community. There were about 300 burrows available each year, but in about one‐third no bird was found.Three biological points stand out above all others. The first is the periodic nestling mortality, which suggests one chick is all the parents can rear even if things go well, which does not always happen. The second is the tight fit of the breeding season, with pressure to migrate near the end of it. This probably means the parents find it hard to food themselves, lot alone a chick, in the last stages, as otherwise the migratory urge would not develop so early. The third is the low annual mortality, which may be as little as 6 per cent. If so, the average expectation of further life would be around 16 years.