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Both birds were trapped, ringed, photographed and measured by Hannu Kärkkäinen.

(1.) Blyth's Reed Warbler Acrocephalus dumetorum 15.6.2008, Suonenjoki, Finland. The supercilium not as clear-cut as usual and the primaries, primary coverts and alula are darker than normal. Still looks as a quite normal dumetorum

(2.) The same bird as in the previous photo. The emargination of P7 is very slight, almost non-existent, which is not normal at all. In addition, P9 seems quite long (slightly longer than P6).

(3.) Marsh Warbler Acrocephalus palustris 7.6.2008, Suonenjoki, Finland. Looks (and is) somewhat long-billed and the primary projection is not terribly long, but again not as aberrant in a profile photo.

(4.) The same bird as in photo 3. The emargination on P7 is an aberrant feature. The same can be said about quite the short P9 (shorter than P6) and even the visible notches on the inner webs of P8 and P7.
Measurements of the birds:
The bird in photos 1-2: wing 67mm
The bird in photos 3-4: