A putative Arctic Tern or `eastern` Common Tern ?

During Sakertour`s Danube Delta – Dobrudja Autumn Tour in 2016 we have seen a quite interesting 2nd summer type Common or Arctic Tern in the coastal Danube Delta, more precisley at Sachalin Bay, a bit south to Sfantu Gheorghe village.  If is really an Arctic Tern this would be only the second proved observation for the country BUT if is an Eastern Common Tern (S. h. longipennis) than this observation could be the first for the country.

sterna-sp Common or Arctic Terns in such plumage are rarely seen in the breeding grounds in Europe (Photo: Tiganov Romica)

Due to the importance and curiosoty of this observation I made this new entry and share all the images we made during that day.

On 31th of August, 2016 we have started the birding day at Sachalin. This wonderfull shallow bay by the Black Sea was packed with birds, especially shorebirds and terns. The weather was clear but very windy, ca. 30-35 km/h east wind made the observation a bit unconfortable. Due to the strong wind birds stayed on the ground and allowed closer approach just the scope shaking was a bit frustrating but never mind.

Right in the beginning we walked by a group of Little Gulls and immediately spotted a strange looking Tern sitting among them very low on the ground.  I immediately put the scope on it and ask the others to follow it if going to fly. I made 3 pictures through the scope with my phone when the bird suddenly took of but fortunately my collegue with it`s DSLR camera took a series of pictures when flew overhead and disappeared amongst a larger group of Common Terns.  We have tried to refound it but our attempt was unsuccesfull.

sterna-sp Digiscoping picture right after the bird was found. The wing feathers were extermly worn at first sight (Photo: Zoltan Baczo)

sterna-sp Dark markings on the secondaries were the main decision point for Common Tern (Photo: Zoltán Baczó)

sterna-sp The first 8 primaries had well defined dark traileng edge good for Arctic Tern (Photo: Tiganov Romica)

sterna-sp When flew against the strong wind held its wings relatively more forward. The rounded head, completly white underwing are in a favour of Arctic (Photo: Tiganov Romica)

sterna-sp Look at the ashy color of the underbody (Photo: Tiganov Romica)

wing1 The secondaries having a relatively darker edge on the upper wing (Photo: Tiganov Romica)

sterna-sp The wing feathers are all one generations (Photo: Tiganov Romica)

sterna Compared to a Little Gull in flight (Photo: Tiganov Romica)

As you can see on these pictures such Common/Arctic Terns with full black bill and extansive black on the head are fairly unfamiliar for us in Europe becouse generally they spending the whole year in their winterring range in Africa OR we are facing to an other supspecies of the Common Tern (Sterna hirundo longipennis) from far Asia which is a rare visitor in Europe!

Here is a list of pros and cons for Arctic:

Pros:

– short, black bill

–  short, dark legs

– form of the head: peak of the head behaind the eyes therefore creates more rounded head appearance than Common Tern has.

–  black cap extending less far towards mantle than Common Tern

– completly white, and translucent underwing

– well marked, narrow black trailing edge of the first 8 primaries

– against the strong wind visible as the bird holding its wings much forward than Common Terns

–  one generation wing feathers

Cons:

–  worn wing feathers, thay all should be changed during the summer

–  dark markings on some secondries and should be whitouth any dark markings for an Arctic Tern

 

Similar observations found on the internet:

Black-billed Arctic Tern

http://www.10000birds.com/portlandica-plumage-arctic-terns-sterna-paradisaea.htm

http://brucemactavish1.blogspot.ro/2016/08/black-billed-arctic-tern.html

https://www.rutlandwater.org.uk/2nd-summer-arctic-terns-at-rutland-water/

 

Eastern Common Tern (Sterna hirundo longipennis)

http://www.birdguides.com/iris/pictures.asp?v=1&f=453786

http://www.birdguides.com/iris/pictures.asp?v=1&f=453784

http://www.birdguides.com/iris/pictures.asp?v=1&f=453785

http://www.pbase.com/blomdahl/image/151348524

http://orientalbirdimages.org/birdimages.php?action=birdspecies&Bird_ID=976&Bird_Image_ID=19141&Bird_Family_ID=

http://www.pbase.com/albert_noorlander/image/163045908

 

The dark markings on the secondaries and the worn feathers suggesting we may facing to a Common Tern but in this case this tern has a differnet jizz anyway than normal Common Tern is Europe.

Pros for Eastren Common Tern:

  • full black bill which was overall shorter and finer
  • dark legs (not black, more like dark brown)
  • dark trailing edge on some secondaries
  • ashy color on the underbody
  • Arctic Tern like jizz

 

sterna sp The overall conclusion is still open, so your comment is really welcome and appreciated…

 

Best regards,

Zoli Baczó

sakertour

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