An Acrocephalus warbler trapped by Bob Rigdon, Dean Bolt and myself in the Chicory at Nitten Field this morning turned out to be a 'Biometric' Marsh Warbler. A small bird overall with wing length at lower end of spectrum for Marsh Warbler, hence our initial caution. However, bill measurements were well below the minimum recorded for Reed Warbler, and were even at the lower end for Marsh. Walinder method and other features also place it pretty neatly in the Marsh camp. If we believe the biometry, and we have no reason not to in this case, then juv Marsh Warbler is not an easy bird to identify in the field. Difficult to judge from the photos, but plumage tones did appear a little cooler than juvenile Reed, pale primary tips, leg and toe colours seemed to fit the descriptions, but these are such subjective characters, even in the hand. I'm now reasonably confident we have got the id correct, but will be contacting others with more experience for opinion before submitting the record. For anyone interested in looking for the bird, good luck, as it won't be easy!