A mystery demystified?

"... any Chiffchaff producing a typical tristis call should be a tristis, providing that plumage and bare-part colorations remain within the limits described..." van den Berg (2009).

I have my doubts about our current approach to Chiffchaffs but, if this is where the goal posts are at, and apparently it is (for now at least), then I had a classic Siberian Chiffchaff in Avon/North Somerset/South Gloucestershire/some geographically schizophrenic location this morning. I was working at the time so, unfortunately, I didn't have DSLR or recording equipment with me, but I'll have another look next week. In the meantime, if you're in the Avonmouth area, take a wander down Lawrence Weston Road, the bird was showing very well (and heard to call) just past the incinerator site in the trees/bushes on either side of the road opposite the brewery distribution depot. In addition, two or three Ruddy Ducks were at the 'square pool' near Avonmouth Sewage Works along with a good dose of native wildfowl.

NB. As often seems to be the case nowadays the reference you need is from Dutch Birding not BB or Birding World, details as follows: van den Berg, A. (2009). Calls, identification and taxonomy of Siberian Chiffchaff: an analysis. Dutch Birding 31: 79-85.