Olivaceous Warbler ID and Iduna Issues

 

Yoav Perlman 

On October 1st Noam Weiss trapped this intriguing Iduna Warbler at IBRCE, Eilat.

Noam is the director of the IBRCE, and is one of the most experienced ringers in Israel. Noam must have handled in his extensive ringing carrier several thousand Eastern Olivaceous Warblers I. elaeica, the default Iduna in Israel, and he was immediately struck by this individual – how pallid and sandy it was, and this amazing bill!profile1

 

Noam understood he had an unusual bird in his hands, and did what an experienced ringer should do in cases like this: he took full measurements of the bird, made sure he had enough photographs in good light conditions, and collected a couple of belly feathers that were shed during the normal ringing process, for DNA analysis. He suspected it could be opaca, the Western Olivaceous Warbler based on its very long bill. There are no accepted records of opaca in Israel, yet…

wing

Naom’s bird was rather large, larger than average elaeica, with a wing length of 67 mm. The wing formula wasn’t helpful – especially the 2nd primary that falls between P6/7 – OK for both species:

The bill length fits opaca, with length to skull of 19.6 mm, but the bill width was too narrow and fits elaeica better – 4.4 mm. Also note the bill shape from below – in opaca it’s supposed to be convex, with swollen mandibles, while elaeica shows straight or slightly concave mandibles:

bill

 

A few other pointers to this bird being elaeica are:

Pale wing panel on secondaries – opaca lacks a wing panel.
Overall tones – though this bird lacks the typically olive-grey tones of elaeica, it still lacks the brown, almost Acrocephalus tones of opaca.
The lores are pretty dark, and supercilium rather pronounced. opaca has a more open-faced impression with pale lores.

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After consulting with members of the Spanish rarities committee, including Manolo Garcia, the consensus on this bird is that it is an unusual elaeica with a deformed bill, and not opaca. But maybe DNA analysis provides different insights? We will know more soon. Thumbs up to Noam for picking out this interesting bird, and sharing the images and information with me.

normal Eastern Olivaceous Warblers

Here are a few images of normal elaeica from Israel. They normally are darker and have stronger olive tones, though this is often hard to perceive in photographs, as it depends on light conditions and on how images are manipulated in editing software. This is an individual in May – look at the pointed and narrow bill:

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And this is a cute 1cy, recently fledged (huge awww factor), after a limited post-juvenile moult. Very short and thin bill:oli

Identification of Iduna warblers has been discussed on Birding Frontiers before – check this post with some images of opaca and reiseri. But always there is more to learn!

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