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Desert Lesser Whitethroat at Filey International

November 18, 2016

By Mark Pearson and Yoav Perlman. Originally published here by Birding Frontiers in October 2016

As in every autumn in recent years, reports of eastern taxa Lesser Whitethroats were rather frequent in recent weeks, mainly along the E coast and N Isles. Several were trapped and DNA samples obtained for ID confirmation. Very often they are first picked up by the ‘trrrrr’ call. It seems that almost every Lesser Whitethroat on the east coast in October has a good potential to be of an eastern origin. One of those that stood out was a very striking individual at Filey on October 17th by Mark Pearson – striking by being such a plain, brown job, that fits well with what would be expected from Desert Lesser Whitethroat Sylvia curruca halimodendri.

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Not really stop press anymore, but to my eyes worth a mention. Siberian (S. c. blythi) and Desert Lesser Whitethroats were always Martin’s favourite, featuring in many posts (e.g. here and here) and in Martin’s Challenge Series: Autumn book too. In the previous posts the taxonomic position of this taxon is discussed (and always good to redirect to this important paper that clarifies the taxonomy of Lesser Whitethroats). I think that now, with current developments in taxonomy and field birding, classic individuals like this can be readily identified in the field.

Handing over to Mark now:

Flushing a small, sandy warbler with strikingly white outer-tail feathers from a field edge just a few metres from the clifftop, especially in the midst of long-term easterlies (delivering Asian waifs to the east coast) couldn’t help but the raise the alarm bells, and from there on it was cat-and-mouse along the nearest hedgerow. Long periods of staring blankly into the hawthorn were followed by intermittently close views as the bird materialised seemingly out of nowhere several times.

Having had several strong candidates for Siberian blythi here over the last few years – including a striking bird a couple of weeks earlier nearby (which not only fitted the visual, but also gave the rattle call) – this bird was clearly something very different. Trying to remember conversations with Martin as well as the features described in the Autumn: Frontiers book were at least partially successful and I roughly recalled the basics (including tail pattern), and after prolonged observations, all were apparently present and correct.

Small-bodied, large-headed, short-billed, short-winged, ‘cute’ appearance; poorly defined weak mask, suffused with brown:

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Sandy brown upperparts, extending concolourously not only over the nape, but all the way across the crown to the base of the bill:

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Noticeably long tail, often cocked:

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Entirely white outer web of T6, and extensive white tips on at least T5 and T4:

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Taking into account the fact that photos of Lesser Whitethroats can often be misleading, particularly regarding the extent and exact shade of subtle plumage tones in different lights, it’s worth pointing out that those which capture this bird’s tones were taken in flat, dull light (and not in bright or sunny conditions that can often ‘over-saturate’ these features); observations fully supported this, to the point that it was almost hard to believe the bird was actually a Lesser Whitethroat at times.

While the assessment criteria of field records of vagrant Desert Lesser Whitethroats is still apparently developing (and my knowledge is limited to say the least), on current understanding and by process of elimination – plumage, proportions, tail pattern etc. – it seems difficult to seriously consider anything else…. thoughts very welcome.

Another small comment by YP: Ageing the bird is possible from these images. PC are worn and brown-fringed (see 2nd image from top), which is typical for young birds. Adult would have broader, fresher, grey-fringed PC. This bird has moulted most of its tail – two central TF pairs are unmoulted, and outer 4 pairs are replaced or growing. This partial moult is also typical for young birds. The central tail feathers are exteremely worn, pointed and brown. The newly grown outer TF have broad and white tips rather than limited off-white tips that are typical for unreplaced young outer TF (see here for demonstration of this).

Replaced adult-type TF typically have more extensive white tips to TF, and more TF with white tips than juvenile-type TF. This complicates the understanding whether a bird has ‘much white’ or ‘little white’. For this, ageing the bird and the TF correctly is essentail. The extreme amount of white shown by the Filey bird is more than any adult-type TF of curruca and blythi can show.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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