Booted / Sykes’ Warbler: SPTA West, 19th October 2019

During their Salisbury Plain ringing session on 19th October, Andy Palmer extracted what looked like a washed out Reed Warbler.  When Ian Grier saw it, he immediately identified it as an Iduna species warbler.  The most reasonable assumption was that it was an Eastern Olivaceous Warbler, Iduna pallida.

Ian ringed the bird and they took a wide range of biometrics, in order to try to clearly identify the species.

Wing Length: 63mm,  Tail Length: 52mm, Tarsus Length: Max: 24.5mm, Min: 21.5mm

Length from tip of bill to nostril 8.2mm, to feathers 9.5mm, to skull 14.0mm

Bill width at nostrils: 4.2mm

Weight: 10.4g

Wing point (i.e. the feathers that make the longest part of the wing): P3 and P4; P2 = P6

Emargination (this is a narrowing of the top part towards the tip of the  feather) P4 = 15mm; P5=12mm

Difference in feather length: P1-P2 = 26mm; P2-P3 = 5mm; P2-P4 = 5mm; P2-P5 = 4mm; P2-P6 = 0mm; P2-P10 = -8mm

Ian also took a number of photographs of the bird to aid with the confirmation of species.  I have been asked to remove the lateral photograph of the bird because it does not conform to the BTO’s social media guidelines. Whilst the ringers in question know that the bird was perfectly well and flew off strongly after processing, it looks a little fluffed up in the photograph.  It is thought that this could be misused by anti-ringing  groups to spread their message: so I have removed it. Apologies to all who have missed it (although a couple of thousand of you have been fortunate enough to see it).


Unfortunately, some of the biometrics did not comfortably fit Eastern Olivaceous Warbler.  As neither Ian nor Andy were overly familiar with this species or the other possible Iduna species, Ian used his contacts within the birding world to get an assessment of the data.  The other two possibilities are Booted Warbler, Iduna caligata, and Sykes’ Warbler, Iduna rama.  At present three experts are split 2:1 Sykes’ to Booted.  The record is being submitted to the British birds Raritis Committee to make their determination, which might well end up as an “either / or” identification.

For any birders / twitchers upset that this was not immediately notified to the wider world, it was not possible to do so. Apart from not having fully identified the species, the site is very close to a live firing range, less than 300m away, and neither the Army nor the Defence Infrastructure Organisation would countenance a large twitch onto the area.



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