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Subject: Common Tern (tibetana) [Print This Page]

Author: brendank Time: 22/04/2012 22:09 Subject: Common Tern (tibetana)

21 April 2012 - Southern Waters

I believe these are likely tibetana although Robson shows the bill as rather strongly bicolored (red base and black tip) for tibetana. Both Robson and Brazil state longipennis has reddish-brown legs so I am not sure leg color is enough for subspecific identification on these birds.

Image Attachment: tibetana1.JPG (22/04/2012 22:09, 54.35 KB) / Download count 468
http://www.hkbws.org.hk/BBS/attachment.php?aid=11358

Image Attachment: tibetana2.JPG (22/04/2012 22:09, 64.99 KB) / Download count 446
http://www.hkbws.org.hk/BBS/attachment.php?aid=11359

Image Attachment: tibetana3.JPG (22/04/2012 22:09, 60.7 KB) / Download count 437
http://www.hkbws.org.hk/BBS/attachment.php?aid=11360

Author: AjaA Time: 23/04/2012 11:38

Why do you think they are tibetana, excluding northern breaders?

We believe that the geograhical variation of Common Tern across Asia is reasonably correctly presented in the BWP update. So, some of the breeding birds as far west as the Ob basin have a blackish bill, as shown here:

http://www.elisanet.fi/antero.li ... irat/hir_aasia.html

for example birds 9, 11 and 12.

The variation is largely clinal, and minussensis is a name inside this cline. That means that giving precise subspecific names in the wintering and migration areas is difficult. Tibetana may lie outside this cline, it should have a distinctly darker mantle than longipennis, but mostly red bill in summer, so it should be close to the nominate in this respect.

Author: brendank Time: 23/04/2012 21:30

There was this photo of the two presumed subspecies seen before. In this picture the difference looks rather marked.

http://www.hkbws.org.hk/BBS/redi ... 6&goto=lastpost

However, now that I see your photos of the terns from Russia it does seem that maybe the terns seen Saturday could be appropriate for longipennis. Perhaps the bird with dark legs seen before was an aberrant i]longipennis.

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