By Christian Perez
A New Philippine Species: Australian Tern split from Gull-billed Tern
The Kennedy guide describes two subspecies of the Gull-billed Tern Gelochelidon nilotica: ssp affinis and ssp macrotarsa. In its taxonomic list version 9.2 released in July 2019, the IOC split the Gull-billed Tern into two species:
- Gull-billed Tern Gelochelidon nilotica (which still includes subspecies affinis)
- Australian Tern Gelochelidon macrotarsa (monotypic – meaning no subspecies)
The migrant Gull-billed Tern is relatively common and widespread in the Philippines from August to April, while the Australian Tern has been recorded only once as a vagrant. The Australian Tern will be listed in the next Checklist of the Birds of the Philippines to be published in 2020.
Single record of Australian Tern in 1971
The Australian Tern is widespread in Australia and disperses in Northern Australia and the south coast of New Guinea during the dry season from October to April. It was recorded in the Philippines on Simunul Island, Tawi-Tawi, on 17 October 1971 by John Dupont and Dioscoro Rabor. In order to explain why this was accepted as a Philippine record, I need to provide references. The sighting was reported by the observers in an article in the magazine Nemouria in 1973 and identified as Gelochelidon nilotica nilotica:
The three specimens taken were sent to the Delaware Museum of Natural History, and later examined there by American ornithologist Kenneth Parkes and identified as Gelochelidon macrotarsa. The reference for this is in the book The Birds of the Philippines. An annotated checklist, by Edwards Dickinson, Robert Kennedy and Kenneth Parkes(page 172), which was published in the UK in 1991. That book was the basis for the distributions in the Kennedy guide. By the way it is in the WBCP library (contact person is Willem van de Ven if you want to see the book).
How to Separate Australian Tern from Gull-billed Tern
While the Gull-billed Tern is relatively common during the migration season, the Australian Tern was an accidental record and the chance of observing one again are extremely low. However, for those who go birding in the southern tip of the country, it is a good idea to keep an eye for Gull-billed Tern and the possible Australian Tern among them.
The reference paper for the separation of Gull-billed and Australian Tern based on physical features is an article entitled Gull-billed Terns in north-western Australia: Subspecies identification, moults and behavioural notes, by D.I. Rogers et al, published in the magazine Emu in 2005, which can be downloaded at:
That is a scientific paper that is not easy to read for most birders. Kennedy simply states that “macrotarsa has a longer bill and tarsus than affinis”. More useful is this extract of a comparative description of Australian Tern provided on the website of Handbook of the Birds of the World (HBW):
“Hitherto treated as conspecific with G. nilotica, but differs in its considerably larger size; differently shaped bill, with culmen more decurved and negligible gonydeal angle; nomadic, opportunistic and kleptoparasitic behaviour; paler grey upperparts; more extensive black patch around the eye and ear-coverts in winter”. (Culmen = the upper ridge of a bird’s bill; gonydeal angle = point on the lower mandible where it turns upwards near the tip)
Well, I realize that it would be a rather unlikely event, but it is good to be aware that the Australian tern has been spotted in the Philippines before, so, who knows, it could happen again!
(photo by Glen Fergus – Own work, CC BY-SA 2.5)
https://upload.wikimedia.org/wikipedia/commons/d/d0/Gull-billed_Tern.jpg
UPDATE IN MARCH 2020: The Rarities Committee examined the three specimen stored at Delaware Museum of Natural History and concluded that they do not match G. macrotarsa. The record was therefore invalidated by the Committee and Autralian Tern will be removed from the 2021 Checklist of the Birds of the Philippines.