I’m sad to say that it seems like I left it too late to learn more about Siberian Chiffchaffs, and it’s my own fault. I visited Dorney Common last week, but was too foolish to look up the exact location of the group of Chiffchaffs that had been so accessible during the freezing weather, and spent a fruitless half an hour up and down a pleasant enough stretch of stream without a single warbler as reward. I saw Wrens and Dunnocks in the stream, several Song Thrushes, and a large flock of Fieldfares, Redwings and Starlings on the common. No Chiffs. Jerry O’Brien tried to put me right …
The right location was the stream running north of the road across Dorney Common, and I returned there this Monday. This is right on the Bucks/Berks boundary, so there were at least county year-ticks on offer. I soon startled a Kingfisher, and instead of belting off along the stream it headed up and over the rooftops, looking like an experimental aircraft. Several Reed Buntings flitted through the phragmites stand in the stream, and I soon heard a Cetti’s Warbler, perhaps more stuttering than usual.
I heard a Chiffchaff but couldn’t locate the singer. Soon afterwards, I found this grey-green Chiffchaff down just above the water level, giving me great close views. I initially believed this greyish-looking bird to be an abietinus-type Chiffchaffs, since I think one such had been reported at the site, showing green fringes to the coverts as well as the remiges and rectrices, and probably a greenish tint to the mantle. On looking at the photographs, I’m less sure; on the pro-eastern side is an absence of yellow tones in the whitish underparts and supercilium, and very cold brown-grey crown and nape. Unfortunately, there were no tristis calls to help me out, only normal Chiffchaff calls from an unseen bird (see below). The only tristis I have heard call was one at Halligarth on Unst in October 2010, and that was a cold brown bird with white supercilium, whitish-buff underparts and warmer buff on flanks, without significant greenish tones (from my views); the appearance of the Dorney bird I saw has more grey and green than the cold brown I saw on Shetland.
I’m struggling to see why this isn’t the bird photographed by Marek Walford, apart from a messier supercilium on the day I visited. There’s been a lot of disccussion of the birds that were present in the cold spell – there’s no guarantee that this one is the same, but why should they have moved on just yet? – and several experienced voices have spoken in favour of Marek’s bird(s) being tristis. A major authority on this issue is Alan Dean, and in his comments on the Dorney birds he said that they may be fulvescens (western form of tristis, with colour tones overlapping with abietinus), if supported by call.
Perhaps this is too subtle for me … I feel I can be excused, if even an über-birder like Ian Lewington has to exercise caution, and the two very different-looking pictures he took of the same supposed tristis at Streatley in Berkshire show what a tough call this is. Jerry has again helped out by re-linking his photos of the bird in 2008 at Sandhurst SF that was accepted as tristis by the BBRC.
I got only a brief glimpse of a second bird, very different in colouration to the first. This was an oily brown, with a short supercilium and white semicircle under the eye. There isn’t enough information in the pics to say for sure, but I think this is just a dark collybita, not showing cold brown tones, or (probably) white enough underparts to be a tristis candidate.
Just a little further up the brook, a Water Rail scurried across a gap, giving me a brief view. I also got rather brief views of a second singing Cetti’s Warbler, and pairs of Grey and Pied Wagtails were flitting about on the opposite (Berks) bank of the stream.