Saturday, 12 February 2011

Sandwich Tern or Cabot's Tern?

Click on image to enlarge.

Trying to work out if this bird can be identified as either a Nearctic or Palearctic bird. Simon and I came across it last week on the Azores. The answer is actually on the bottom of the left leg but I can't read it!
The identification of 'American Sandwich Tern' (also known as Cabot's Tern) has been dealt with by Garner et al in Dutch Birding Vol:29:5 but I still can't work it out :-)


Anonymous said...

Well, the white-peppered nape would indicate European bird according to Garner, and the bill seems long and decurved enough as well. A full set of new primaries in winter is also better for European according to Garner.
Now, the amount of white along the inner web and tip of primaries is lower than European, and seems much better for Cabot.
I guess I share your lack of confidence about its ID...
Plate 410-411 of the DB paper indicate that European primary pattern is variable, and I have some pics of local French birds in winter with similarly narrow white fringe, so may be european is a better bet???

Peter Alfrey said...

Hi Pierre,
Yes- it seems to show mixed characteristics.
Apparantely the ring is not BTO- so maybe if someone recognises the type of ring- that can give us a clue too.
Hopefully Vincent will get some super sharp shots where we can read what it says.

Peter Alfrey said...

I heard back from Martin Garner- here is the reply (thanks Martin)

Hi Peter

Had bit more of a look at the Azores Sandwich Tern- beware hastiness- my cursory glance at the photos few days ago and I saw the bird in flight and saw primaries and esp. primary coverts and thought 1st winter- However on another longer look it clearly has most/ all adult type primaries so the in-flight shot might be miss-leading- it could still be an advanced first winter but I am not sure of age. Retained juv tail feathers are sometimes the last ‘dark marked’ feathers to go- but can’t make them out here. Nominate birds (especially) I think are not always easy to age post the New Year. Aging aside the head pattern- shorter black ‘nape’ feathers with whitish tips and bill length and shape are all v pro- sandvicensis. The position of the gonydeal angle might be helpful sometimes- around mid point on acuflavida and more obviously in the basal half on sandvicensis (as here). Head and bill alone make it European type for me- the wing pattern is variable and I can see this one is at the thinner end of white trim, but these occur. The thicker shorter bill of acuflavida and long greasy black nape feathers will jump out you when you do find that Cabot’s tern on the Azores. PS I am not sure every individual is even necessarily identifiable anyway- though I think a good majority should be. As with all subtle taxa- the obvious ones are easy and these are the one we want to find.

Hope that helps


David said...

comparing our photos taken on TCR with DB paper, none of the decribed features for cabot could be actually matched, so we had already little hope for that species! and if now all pro are confirming that it is more likely a european bird..maybe next time to find a cabot in Azores! info on the bird's origin through the ring can perhaps be guessed from a look on the euring website and here where all project are detailed with ring colour details and so on:
And what about all ducks seen in azores this winter with some of them occuring on both sides of the ocean?? Can the pro tell us if for instance the azores greater scaups are from nearctic or palearctic origin?

Peter Alfrey said...

Is that you Monti?

The narrow primary fringes are a pro- Cabot's feature but apart from that it all looks pro Sandwich.

Did you find a match for the ring? That would be interesting.

As for the Scaups-there were a few discussions with some suggestions that adult males in the states were closer to Lesser Scaup in appearance- with coarser markings on the upperparts- but as for females- who knows? Be interesting to find out.

Larus said...

This tern was born in Poland in 2009!
I have got a number read by Olaf Jonsson from Sweden.
you can see some pictures taken during ringing this chick:
best wishes
Szymon Bzoma

Peter Alfrey said...


Dominic Mitchell said...

More than a year after this post and the ensuing comments, I caught up with the two Sandwich Terns in Cabo da Praia fishing harbour today. I noticed that one is ringed - surely the same bird? Amazing to think that it was born in Poland and has come to the Azores either for two consecutive winters, or perhaps permanently ...