Status, biometrics, moult and possible relationships of the South African population of Roseate Tern

The breeding population of Roseate Terns in southern Africa was estimated to be 250–260 pairs in 2000. Adult birds caught during nocturnal tern roost mist-netting on Bird Island and at Cape Recife, both in Algoa Bay, were closest to their North Atlantic counterparts in wing, bill, total head length, tail and mass measurements. Adult moult differs from that of other populations. The two series wing moult of adults begins in the austral winter and lasts through summer; three feather series may be present in the primary remiges of immature birds. Evidence at present points to reproductive isolation of the South African population and to a degree of migratory behaviour, the extent of which remains unknown. However, size, breeding periodicity and low inter-annual return rate of ringed adults in successive seasons suggests a possible link with the southern Madagascan population.