Wednesday, July 27, 2011

Salt and pepper

Yesterday I joined Yosef for his ongoing project of colour-ringing terns at Atlit Saltpans. These saltpans hold Israel's largest tern colony, and are an excellent birding site altogether.
We arrived in time to have a quick look at the colony before setting the nets up. We had this interesting tern - it's very dark both above and below, with a narrow white cheek stripe. The bill is long and red. The bird was large and powerful, like a normal Common Tern. It incubated non-stop, so unfortunately we couldn't see the legs at all. I waited for half an hour for the bird to stand up or fly off, but had to give up and let it be; the nets were waiting.
This bird reminds me very much of this amazing bird ringed by Yosef last year. Whether our bird had rings or not I do not know. The plumage colours are superficially similar to White-cheeked Tern, but size, structure and bill are wrong.
There is a very interesting article by Sean Nixon in Birding World 24: 211-215 illustrating the identification of eastern Common Terns. It describes in detail longipensis, and more briefly tibetana. But to my eyes this bird is far too dark for any longipensis (which should show a dark bill) or tibetana. I have no idea what the dodgy form sinunensis looks like, but I assume it should be paler anyway.
However, one thing I learned last night is that the amount of variation in Common Tersn in huge, and it occurs in all aspects: size, plumage tones, bare parts. So whether this bird is an extremely extreme Common Tern, an 'eastern' Common Tern (breeding in Israel?!), or a hybrid Common X White-cheeked Tern we will probably never know. I will certainly try to return and have better views of this fascinating bird. Of course, any comments on this bird are most welcome.

This is the bird incubating:

And here in comparison to a 'normal' Common Tern:

Anyway, as night fell we started catching terns. We were joined by the Hula team, Rony and Michael. Even though the wind was strong all night long, we had a decent catch of 30 Common Terns, 15 Little Terns (including an ancient retrap from the mid-1990's!) and for a late bonus a beautiful adult White-winged Tern.

Common Tern - adult (4cy+)
Rony the magician
Common Tern - 2cy. Note the very worn unmoulted primaries, PC, alula and GC, and dark lesser-coverts bar. Bill is almost completely dark, and crown mixed with brown. Most Common Terns spend their first year and a half somewhere in the southern oceans or offshore Africa, and only few return north in their first summer.

Little Tern - adult

Little Tern - juvenile
White-winged Tern - adult

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