Unfortunately non calling, legs brownish (not blackish) and a fair amount of pale on lower mandible, strong supercilium lacking eye crescents, very white underside and grey nape. On the bad side for Siberian Chiffchaff (tristis) it lacked buffy tones - especially around cheeks, it showed extensive yellow on body feathers at bend of wing and yellowish top to rear flanks, perhaps a hint of yellow in supercilium, in sunlight it also showed alot of olive in plumage including scapulars and hints of olive streaks in the mantle- perhaps even crown. It was half interested in tristis song playback (hopping up the branch and looking at me) but did not react with wing quivering, and very soon lost interest. Perhaps a intergrade or eastern abietinus or just an odd collybita!