Its only 3 days ago! Had such a full on few days and just catching up. Last monday was the start of the 3 day guided event at Spurn which started bang on with singing Marsh Warbler in the canal hedge thanks to finder, Andy Roadhouse. If they are singing they are not too tricky. Non-singers being more problematic. In spring: besides being more olivey green above (yellowy-rumped) with bits of yellow below than Reed Warbler (which are browner, rust rumped and no yellow below) the face often looks different. To me the white eye-ring on Reed Warbler nearly always jumps out is the most prominent feature of the face followed by the weak thin pale ‘squiggly’ stripe running from eye to bill. The bill is long.
On Marsh Warbler the face is more open (even ‘hippolais warbler-like) and any pale around the eye less obvious than on Reed with the pale area between bill and eye, being big, pale and open (not thin and squiggly as on Reed).
Here is last Mondays Marsh Warbler compared with a Reed Warbler photographed in the nearby canal zone.
Reed Warbler, Canal Zone, Spurn, May 2012. A prominent white eyering is often the first thing noticed when head of a skulking Reed Warbler pops out!