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Antarctic Tern

Most Northerly Record Ever

by Chris Kehoe

With strange chequered markings in the tertials and  scapulars and worn blackish coverts, this young tern caused some initial head scratching. Many Antarctic Terns disperse northwards in the post breeding season and many young birds remain out at sea. This occurrence of a moulting juvenile Antarctic Tern found 7ookm further north than previous records suggests it’s not an entirely unlikely potential vagrant to the Western Palearctic, either via an Indian Ocean route or even perhaps via the Atlantic.

 

 

Madagascar (oct.-nov. 2013) 424b

This moulting juvenile tern was photographed on October 31st 2013 by Jean Neuray near Maroansetra in northeastern Madagascar during a Birdquest tour I was leading. When first seen briefly in flight, and against the light, a very pale trailing edge on the inner wing, glimpses of a neat dark trailing edge on the underside of white looking primaries and the overall structure created a strong impression of a young Arctic Tern – a vagrant to the tropical Indian Ocean with no previous records in Madagascar. However, when followed up and found settled near a few wintering Common Terns, Arctic was quickly ruled out. In particular the dramatic checkered pattern on the tertials is all wrong for Arctic Tern, the remaining juvenile mantle and scapulars are too dark and heavily patterned, the legs are a little too long and the plumage wear is more advanced than would be expected for a juvenile Arctic at such a date. Still, the bill proportions are similar to Arctic as is the head pattern with that big dark ‘panda’ eye patch, though it looked a little bulkier than Arctic around the head and chest. After a few moments the bird flew off with an elegant bouncy flight, viewed directly from behind but in better light than previously the secondaries were now seen to be very pale uniform grey, less white looking than on a juvenile Arctic, the rump and tail were mostly white though with greyer looking tail sides.

At the time I was perplexed by this combination of features, it was clearly not consistent with the appearance of any of the regularly occurring Malagasy tern species, though I vaguely recalled that the such a tertial pattern was a feature associated with Antarctic Tern and I tentatively suggested this possibility to my colleagues. As we were en route to the remote Masoala Peninsular to search for Helmet Vangas there was no immediate prospect of making further progress, all my relevant literature was at home and there would be no internet access, or even phone coverage for many days. When we eventually arrived in Antananarivo nearly a week later a quick Google image search seemed to confirm that Antarctic Tern was indeed the likely solution. Though no birds in exactly the same plumage state were depicted there were a few images of fresher plumaged juveniles showing a tertial pattern closely matching the Maroansetra bird.

juvenile Antarctic Tern, Sterna vittata vittata, 9 Aug 2009, Cape Columbine Nature Reserve, South Africa. Trevor Hardaker.

juvenile Antarctic Tern, Sterna vittata vittata, 9 Aug 2009, Cape Columbine Nature Reserve, South Africa. Trevor Hardaker.

juvenile Antarctic Tern, Sterna vittata vittata, 9 Aug 2009, Cape Columbine Nature Reserve, South Africa. Trevor Hardaker.

juvenile Antarctic Tern, Sterna vittata vittata, 9 Aug 2009, Cape Columbine Nature Reserve, South Africa. Trevor Hardaker.

Once back home it was possible to consult the literature (though rather little of use was found there) and to discuss the bird’s identity with others. The eventual consensus was that Antarctic Tern was indeed the best fit. Though few people knew the species well, and none were familiar with it in this particular plumage state, all were agreed that, realistically, it could not be any other species though it was necessary to extrapolate from images of birds in rather fresher plumage in order to secure a good match for Antarctic. One proviso though was that the immature plumages of the closely related and generally similar but very rare Kerguelen Tern seem to be virtually unknown, though young birds perhaps share the diagnostic grey tail of adults as do immatures of several other grey-tailed tern species.

Antarctic Tern breeds on various Subantarctic islands and on the Antarctic Peninsular during the austral summer but many disperse northwards soon after breeding. South Africa holds some quite large but very localised concentrations of post-breeding birds between April and October but the species then seems to lead a largely pelagic existence before returning to the breeding areas. Non-breeding birds also occur in southern New Zealand and along the coast of Argentina. Vagrants have been recorded in southeastern Brazil, in southern Australia and at Walvis Bay in Namibia.

The bird at Maroansetra therefore appears to represent the most northerly record ever, at 15.45°S it was approximately 800km further north than vagrants recorded in Brazil and Namibia (both at approximately the latitude of the Tropic of Capricorn) which are both about 700km north of areas of regular occurrence.

1cy Antarctic Tern Sterna vittata tristanensis. 26th Aug 2006 Mauritzbaai, South Africa. Trevor Hardaker

1cy Antarctic Tern Sterna vittata tristanensis. 26th Aug 2006 Mauritzbaai, South Africa. Trevor Hardaker

1cy Antarctic Tern Sterna vittata tristanensis. 26th Aug 2006 Mauritzbaai, South Africa. Trevor Hardaker

1cy Antarctic Tern Sterna vittata tristanensis. 26th Aug 2006 Mauritzbaai, South Africa. Trevor Hardaker

1cy Antarctic Tern Sterna vittata tristanensis 9th August 2009 Cape Columbine Nature Reserve, South Africa. Margaret Hardaker

1cy Antarctic Tern Sterna vittata tristanensis, 9th August 2009 Cape Columbine Nature Reserve, South Africa. Margaret Hardaker

1cy Antarctic Tern Sterna vittata tristanensis, 9th August 2009, Cape Columbine Nature Reserve, South Africa. Margaret Hardaker

1cy Antarctic Tern Sterna vittata tristanensis, 9th August 2009, Cape Columbine Nature Reserve, South Africa. Margaret Hardaker

How often Antarctic Terns reach so far north into the tropics is obviously unknown but there is surely a chance that some may be overlooked, especially once any distinctive juvenile features have been lost. In overall appearance Antarctic Tern is somewhat intermediate between Common and Arctic Tern though generally closer to the latter, both in plumage (seemingly including a simple wing moult strategy in adults) and structure. As some Antarctic Terns come into contact with wintering Common Terns in the Indian Ocean the possibilty must exist that an immature in particular could end up following flocks of that species as they return northwards. Arctic Tern is only a vagrant in the Indian Ocean north of South Africa with records in Somalia and Oman as well as in the Arabian Gulf and the Red Sea. However, anyone encountering a potential Arctic Tern in this region should be aware that Antarctic Tern also needs to be carefully considered. It may not be too outlandish to suggest that this highly pelagic species is also a potential vagrant to the Western Palearctic via an Atlantic route where both Common and Arctic Terns could act as carrier species, far stranger things have happened.

juvenile Antarctic Tern Sterna vittata vittata,18th May 2008, Mauritzbaai, South Africa. Trevor Hardaker

juvenile Antarctic Tern Sterna vittata vittata,18th May 2008, Mauritzbaai, South Africa. Trevor Hardaker

juvenile Antarctic Tern Sterna vittata vittata,18th May 2008, Mauritzbaai, South Africa. Trevor Hardaker

juvenile Antarctic Tern Sterna vittata vittata,18th May 2008, Mauritzbaai, South Africa. Trevor Hardaker

Thanks to Pete Morris, Klaus Malling Olsen, and Trevor Hardaker for useful discussions and comments and to Jean Neuray for capturing such a sharp image of the Maroansetra bird from a moving boat. Also special thank to Trevor and Margaret Hardaker for use here of their wonderful images.

juv and adult Antarctic Tern Sterna vittata georgiae, 15th Jan 2010 Grytvikren, South Georgia. Trevor Hardaker

juv and adult Antarctic Tern Sterna vittata georgiae, 15th Jan 2010 Grytvikren, South Georgia. Trevor Hardaker

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