11 Aug 2014

Possible halimodendri Central Asian Whitethroat – Dhahran Hills

As posted previously I found an unusual looking Lesser Whitethroat on my local ‘patch’ on 12 April 2014. I did not hear the bird call and neither did I see it’s tail pattern, but on plumage it looked very odd and I could not fit this bird into my ideas of any of the Lesser Whitethroat complex and have spent some time trying to find out what subspecies, even approximately, this bird might fit into. The bird did not, to me at least, look like a typical Lesser Whitethroat, Desert Whitethroat, Central Asian Whitethroat or Hume’s Whitethroat, so I hypothesized that maybe it came from the hybrid overlap zone or was apale blythi? The most striking feature of the bird was the uniformly coloured head and mantle and what appeared to be a very long thin bill and dark eye. As a result I contacted a number of experienced birders who had knowledge of the group and received a number of very interesting comments.
Neil Morris from Qatar mentioned “Given its structure and grey mantle and scapulars - the answer might lie closer to a pale humei-type population rather than halimodendri/blythi which presumably would show brown/sandy tones on the back whether large or small in structure? The other option is pale blythi, but my knowledge of just how pale they get is limited, and given it's a disputed taxon, it was probably safer to go with halimodendri”.
Alan Dean said “that if this bird had been encountered in the UK observers wouldn’t immediately suspect an ‘eastern’ bird”.
Lars Svensson, who probably has as much knowledge on this group of birds as anyone and who has looked into the Lesser Whitethroat complex in some detail kindly sent me his thoughts on the bird “A first-winter halimodendri if you asked me. But when saying so I am working on probabilities. It is no exact science! But from my experience, such labeling would be reasonable”.
Martin Garner mentioned “he don’t think it was halimodendri at all. All the ones in the UK that are definite on DNA and follow up studies had a tiny primary projection and don’t really look the colour tones of your bird. I think you have curruca or blythi on plumage tones and structure. Hard to be sure as its open but bill looks pretty beefy too – better for blythi/ curruca”.
As you can see there is little agreement over what are the key features of Lesser Whitethroat taxons.
Possible halimodendri
Central Asian Whitethroat - halimodendri
The trouble with this group of birds is it is a bit of a minefield, with mtDNA analyses not according clearly with morphological characters. There is no taxonomic consensus among different authors, neither concerning circumscription of taxa nor regarding species limits. Many authors judged the morphological variation within the Lesser Whitethroat complex to be clinal, from the palest desert form minula through the dark form curruca of the temperate forests to the even darker mountainous althaea. The taxa differ mainly in shades of brown and grey, wing length, tail length and wing formula, and in many cases single individuals are difficult to diagnose with certainty. The northern birds inhabiting temperate forest, curruca and blythi (often not recognized as a valid taxon), are generally larger and darker on the upperparts than lowland desert and steppe forms that have paler sandy upperparts colouration. The birds we probably get in Saudi Arabia are curruca, blythi, halimodendri and althaea with most probably referring to halimodenedri (Neil Morris & my own data).  Although these different taxa are generally identifiable as unique clades by DNA, diagnostic morphological features useful for identification at an individual level are few and subtle, and many individuals cannot be identified with certainty. A recent paper considers the southern limits of the Central Asian lowland desert forms uncertain and probably overestimated and suggests that minula that was previously regarded as occurring in the region is confined to a small area of China and is thus not likely to occur in Arabia.

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