Tuesday, March 29

Isabelline Warbler !?!?

Hi there,
The last few days were quite slow with not many birds at the ringing station and nothing out of the ordinary around.
This morning, yet another slow ringing session with about 40 birds. At around 7:00 I was sitting at the ringing station and was surprised to take a strange looking Iduna warbler out of the bag. First impression was a bird with a very big and wide based bill. I showed the bird to Francis Argyle who was sitting next to me and he had the same immediate impression. More looks at the bird and some measurements made us think we might be holding an Isabelline Warbler Iduna opaca.

As I mentioned, the first impression was created mostly by the unusual bill. Both Francis and I are experienced with the Eastern Olivaceous Warbler Iduna pallida, and actually we ringed two birds of this species just before we handled this bird. The width of the bill at the lower mandible feather line was 4.5 mm, according to Svenson's book, this measurement is well beyond the overlap zone between the two species, of course in the opaca zone. The shape of the bill was also better for opaca with the sides giving a slight convex look.

The face pattern, with a pale lore and short Eyebrow is also good for opaca.

Unfortunately, during the 1.5 hours we kept the bird, no other Iduna was caught so we haven’t a head to head colors comparison, but I had a feeling that this bird is slightly browner grey then the "normal" birds I know from Israel. The wing looks rather uniform with no prominent pale wing panel.

 The other measurements obtained:
Wing length- 65mm
Tail length- 51mm
Body mass- 9.0 gr.
Bill to skull- 16.9mm(in the overlap zone).
Bill width- 4.5mm
Bill depth- 2.8mm
WP- p4

We released the bird after Bram, Teun, Johannes (our volunteers) and 4 of Johannes's friends looked at the bird. All together we were unsure about the bird's identity. None of us have any experience with Isabelline Warbler and I would appreciate any comment and thoughts about this bird.    If we are not big stringers, this might be Israel's 1st record!

 on Sunday, Roni made his way back to his icy homeland. Roni was a great help for us during the last month and we are all looking for the next spring ;-)
Roni with his "dream bird"


  1. the bird was re-captured on Thu' while i was around. to me this looks like an aberrant 'pallida'. the white on the edge of the tail feathers is something that won't work for any 'opaca'.

    never the less the bill does look wider than the usual 'pallida'.

  2. Hi guys! Good catch and an aberrant bird in many ways. I think though that this might still be a pallida. Among the birds we ringed at the station in spring 2009 there was a few odd ones. For example, I measured a few birds with above 19 mm in bill-skull (17,4 mm max according to Svensson). Also a few wide-billed birds noted with almost convex sides of bill. Point is that the variation among birds passing through Eilat seems to be very extensive and to clinch an opaca in Eilat I would personally have to enhance my "braveness" first. :) It might still be an opaca, I have to little experience to say for sure though.

    See you soon!