I'm trying to identify seabird species from my photographs. A birder has identified one bird in my photos as common tern but when I looked it up online (I don't have a bird book with me), most common terns have a reddish bill whereas the one I pictured has a black bill.
Actually, I beg to differ. Individuals of many species change their bill colour with age, sex and breeding season and it usually correlates with physiology. For example: the bill of male house sparrows (Passer domesticus) changes within the year cicle - in breading season they have black bill (correlates with testosterone), whereas in winter, their bill becomes yellowish. The bill colour of females and juveniles stay pretty much the same across the year cycle.
Common terns have black bill in winter, orange-reddish with a black tip in the breeding season. It may have to do with signalling by carothenoids. The upper bill of the juvenile common terns is black, the lower bill is orange. It would be usefull tough to see that picture, if you think it's something else then common tern (Sterna hirundo)
Thanks for the responses!
@Attila: I did come across a few abstracts for other bird species that suggested changes in bill color relating to breeding season but hadn't found any specifically for terns. Are there any articles you could suggest for reading? I'm also attaching the photo taken in central Philippines in April 2011 during a dolphin survey. My colleagues and I have slowly been trying to identify seabirds we've encountered during these surveys which has been difficult to do without a good field guide to birds.
Dear Jean,
After a hash search I found two articles about Roseate Tern bill colour:
http://www.jstor.org/discover/10.2307/4083373?uid=3738920&uid=2&uid=4&sid=21101778175277
http://www.jstor.org/discover/10.2307/4160777?uid=3738920&uid=2&uid=4&sid=21101778175277
and here are two plates on common terns (Sterna hirundo) from field guides:
http://www.google.com/imgres?um=1&hl=hu&sa=N&tbo=d&biw=1280&bih=860&tbm=isch&tbnid=5lJ2vmub8SkLXM:&imgrefurl=http://www.avibirds.com/euhtml/Tern.html&docid=_faOn8wEocofpM&imgurl=http://www.avibirds.com/platen/Visdiefm.jpg&w=500&h=308&ei=vusUUbHeAcKztAaAzoHQBw&zoom=1&ved=1t:3588,r:49,s:0,i:238&iact=rc&dur=1862&sig=115318694198699851855&page=3&tbnh=174&tbnw=274&start=45&ndsp=25&tx=172&ty=55
http://www.google.com/imgres?um=1&hl=hu&sa=N&tbo=d&biw=1280&bih=860&tbm=isch&tbnid=PRKOj3MzphlntM:&imgrefurl=http://greatgullisland.blogspot.com/2012/03/roseate-terns-in-different-places-have.html&docid=lxqQ7eMqBmbjuM&imgurl=http://3.bp.blogspot.com/-d-3vK4mAUKE/T2jRT5ljdyI/AAAAAAAAACQ/R3xrPyPaFDo/s1600/roseate_2.jpg&w=1004&h=1600&ei=vusUUbHeAcKztAaAzoHQBw&zoom=1&ved=1t:3588,r:1,s:0,i:85&iact=rc&dur=5934&sig=115318694198699851855&page=1&tbnh=180&tbnw=112&start=0&ndsp=20&tx=71&ty=94
It is widely accepted that red or orange bills are signals of the bearers quality, and usually is correlated with immune capacity.
About the picture: I also think that the birds photographed by you are Common Terns, but I am not familiar with the Sterna fauna of the Philippines (so as far as I know, it may be something very similar to the Common Terns).
Dear Jean, You might find something here, although in German:
https://www.researchgate.net/publication/234615883_Die_Unterscheidung_von_Fluss-_Sterna_hirundo_und_Kstenseeschwalbe_S._paradisaea?ev=prf_pub
But there are many pictures and an English summary. Peter
Article Die Unterscheidung von Fluss- Sterna hirundo und Küstenseesc...
thank you for all the helpful links.
@Peter: The photos will do for now though I'm looking for an app to translate it later.
@Attila: According to the Wild Bird Club of the Philippines, both common and roseate terns can be found here but from the links, mine looks to be common tern.
Dear Jean,
now that I saw the photograph and understood where and when it was taken, it seems to be clear that the birds are Common Terns indeed. Roseate Tern would have much shorter and redder legs and should show an obvious pinkish (roseate) flush on the underparts.
What obviously has confused you is the colour of the bill. Most photographs in the internet and most field guides only show the nominate subspecies from Europe, North America and West Asia, which wears the red bill with a dark tip. But birds occuring in winter in the Philippines belong to the subspecies longipennis (some perhaps also to tibetana) from East Asia.
Typical features of S. h. longipennis in adult summer plumage (which they wear from April onwards) compared to the nominate subspecies are the black bill (which is also slightly shorter than in nominate and much shorter than in Roseate Tern), the darker, more brownish legs and especially also the darker, greyer underparts with contrasting white cheeks.
The birds in your photograph show all these characters, so I have no doubt that they are Sterna hirundo longipennis.
Hope this helps. Best wishes,
Peter
For tern identification and ageing/sexing of the different species present in the Palaearctic and Nearctic regions you can check this excellent book:
MALLING OLSEN, K. & H. LARSSON (1995). Terns of Europe and North America. Christopher Helm, A & C Black. London. 175 pp. + photos.
Hi again.
Read also the texts on e.g. Sterna hirundo and S. dougallii within the series BWP Updates, which are very useful and contain a lot of information on different subjects, including morphology. The ones on these species were published in 2004 (vol. 6, Nos. 1 & 2).
Hi.
Another interesting and useful reference is the next book:
ENTICOTT, J. & D. TIPLING (1998). Photographic Handbook of the Seabirds of the World. New Holland Publishers Ltd. London - Cape Town - Sydney - Singapore. 234 pp.
- Badges
- Science topic
- Similar topics
- Biological Science
- Zoology
- Ornithology