When asked by another SUNBIRD leader if I would prepare his next Monthly Marathon solution, owing to his busy tour schedule, my first reaction was `not a problem'. My second reaction, on seeing the photograph, was `me and my big mouth!' The bird in Monthly Marathon photo number 212 (Brit. Birds 97: plate 381, repeated here as plate 87) looks a nightmare to identify. I would like to say that there is an obvious solution, but there isn't, not for me at least! It is clearly a passerine, and the combination of a plain tail and lack of any distinctive coloration or prominent field marks should lead us, if only by eliminating all other possibilities, eventually to a warbler (Sylviidae) of some description. We now begin the more detailed examination process and, on a bird as dull and nondescript as this, the two really useful features we can see are a rounded and obviously86. Paddyfield Warbler Acrocephalus agricola, St Mary's, Scilly, October 2001. graduated tail, and the plain, unmarked and quite long undertail-coverts, which reach about halfway along the underside of the tail. This combination of characters rules out Phylloscopus, Hippolais and Sylvia warblers, all of which possess either a squaretipped or a slightly notched tail, and short undertail-coverts. Could the mystery bird be a Cetti's Warbler Cettia cetti? Cetti's Warbler has a strongly graduated tail, like that of our bird, and, unique among European warblers, has only ten rectrices, which would seem to match the number visible in the