Siberian chiffchaff (Phylloscopus (collybita) tristis) is a leaf-warbler which is usually considered a subspecies of the common chiffchaff.
It is also regularly recorded in western Europe in winter
It is a dull bird, grey or brownish above and whitish below, with little yellow in the plumage, and the buff-white supercilium is often longer than in the western subspecies. It has a higher pitched suitsistsuisit song and a short high-pitched cheet call. It is sometimes considered to be a full species due to its distinctive plumage and vocalisations, being similar to P. s. sindianus in these respects.
Common chiffchaffs (of the nominate race) and Siberian chiffchaffs do not recognize each other’s songs.Pending resolution of the status of the form fulvescens, which is found where the ranges of common chiffchaff (of the race abietinus) and Siberian chiffchaff connect and may or may not be a hybrid between these, tristis is maintained in P. collybita by most checklists.