Fluctuation of numbers of waders in south-eastern Tasmania

Abstract

South-eastern Tasmania, at the limit of the winter range of migrant Palaearctic waders, is ideally situated for the study of variation in numbers. Two-monthly totals are given for migratory species from January 1965 to December 1966 and monthly totals for all species from January 1967 to December 1968. Most migrants arrive from August to October and leave between mid-March and early May. Only Tringa nebularia increases throughout the wintering period. In most species migration and moult of flight feathers are probably mutually exclusive. Varying proportions of some species remain throughout the breeding season. Probably these are immature birds, and varying numbers result from independent migrations of adults and immatures. The Macarthur-Wilson model for determining the equilibrium number of species on archipelagos appears to be applicable to waders in south-eastern Tasmania. It is suggested that equilibrium has been reached and that the additions to the Tasmanian list since 1958 are because of increased observation. Reasons why some species fail to become established are discussed.