• Potential problems with photographs
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Potential problems diagnosing tristis from photographs

When using photographs to assess the plumage features which distinguish tristis from other subspecies, it is important to use images of individuals in reasonably fresh plumage. Only then are the critical range and balance of hues accurately manifested. As the birds wear and bleach, critical hues can fade and disappear while - as some colours wear and fade more than others - some hues may even become more apparent, owing to enhanced contrast with faded areas in the plumage. During mid-summer, for example, some individuals (second calendar years especially?) may become so faded and deficient in colour that it is impossible to assign them to any particular subspecies on the basis of plumage colour.

In a UK context, 'Siberian Chiffchaffs' are unlikely to be encountered in mid-summer. However, the pre-breeding moult of tristis is relatively late compared with abietinus and collybita and, in consequence, tristis encountered during March and April can appear confusingly worn and dishevelled as a result of wear and body-moult. The gallery here includes an image of such an individual, photographed at Portland, Dorset, UK, in April 2008. This photograph also indicates how a 'colour sheen' can be imparted to plumage by intensely green surrounding vegetation.

Even when individual Chiffchaffs are in reasonably fresh (and 'representative') plumage, obtaining photographs which capture accurately the critical balance of olive, yellow, grey, brown and buff is not easy. The balance and intensity of these hues is susceptible to several factors, including light conditions, white-balance of camera, and the colours of surrounding vegetation. Photographs of a given individual can vary widely and, in extreme cases, a photograph can even suggest the 'wrong' subspecies. Images taken in overly bright light are especially likely to suffer from over-exposure and colour dilution or loss. In diagnosing 'Siberian Chiffchaff' from photographs, this is a serious source of problems. Further comments on this issue, and examples of varying images, were included in Noeske & Dean 2006 ('Siberian Chiffchaff' in Europe: photo forum, Publications/Articles, www.club300.de). When a long series of photos has been obtained, these can be compared with the appearance of the individual as carefully assessed in the field, and there is a much better chance of obtaining a representative image. 'One off' photographs are unlikely to be truly representative and are very difficult for 'records committees' to assess with confidence.

The images of 'Siberian Chiffchaffs' here have been taken 'in the hand' or objectively assessed by the photographers as matching the basic appearance of the bird 'in the field'. Apart from the Portland individual photographed in April, all others are either fresh or not unduly affected by moult or wear. The images were taken in various months and are arranged chronologically: from September, through the winter and spring, and up to June i.e. a seasonal 'cross-section'. They were taken on the breeding grounds in Siberia (1), the wintering grounds in India (1), on migration in China (1), on migration in Central Asia (3), and in the UK (5, including 2 images of the individual at Portland). I thank the photographers (column 4) for providing these instructive images.

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