The occurrence of the Asian subspecies of the Gull-billed Tern (Gelochelidon nilotica affinis) in the Darwin region, Northern Territory

The Asian subspecies Gelochelidon nilotica affinis of Gull-billed Tern breeds in Asia and migrates to northern Australia during its non-breeding season, which is the Australian wet season/summer. A substantial non-breeding population of this tern occurs in northwestern Australia and it is also an uncommon but regular visitor to the northern coasts of Queensland. However, G. nilotica affinis remains infrequently reported in the Top End. This fact has prompted us formally to report its occurrence in the Darwin region. Interestingly, our own and other recent reports fall outside its normal wet season/summer visiting period in northern Australia. We comment on the importance of recognising and recording this migratory tern, which is separable from the Australian-breeding subspecies (G. affinis macrotarsa) with some care in the field, and include some guidelines to identification of these terns in the field.