Briefly. There were two clear features on this otherwise (in the dull light conditions) dull medium brown and tan Chiffchaff that lead me to suspect a possible tristis: a single narrow indistinct pale buff wing bar (formed by the pale buff tips to the greater coverts) and an olive tinged rump. I could not discern any grey tones on the upperparts (nor any green or yellow anywhere). The tan colouration refered to the underparts. Unfortunatley the bird was not heard to call.
The bird showed well, albeit for 5+ minutes, 09.05-0910, keeping low close to the water at the base of a rose-hip (in the centre of the pond) then lost as it moved away towards the hawthorn hedge. For a milli-second at 10.06 a dull brown Chiffchaff flew back in to the shrubs (rose-hip, hawthorn) and lost.
Due to work commitments I couldn't give it any more time.
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Despite Chorlton WP having it's own thread, I thought this bird deserved one of it's own, for the time being at least.
Pete Hines found a likely Siberian Chiffchaff (tristis) here this morning in the area of the pond near to the childrens play area, the bird has apparently all the suitable features for this race of Chiffchaff which is a true county rarity and pretty scarce through out the country (probably rarer than YB Warblers at the moment!). Identification of tristis is however potentially difficult with another eastern race of Chiffchaff (abeitinus) often overlapping somewhat in features and call (a 2006 county bird called like perfect tristis but showed some plumage characteristics inconsistent with that race), if the bird hangs around (please...just one warbler hang around) it will well be worth an educational look atleast.