Sedge Warbler
Acrocephalus schoenobaenus

Sedge Warblers are fairly common in the UK and can be seen in reed beds on marshes and rivers. Unlike some other warblers, they can often be seen in the open. Sedge Warblers winter in Africa and are usually only summer visitors.
 

1: Bowling Green Marsh RSPB reserve, 19/06/2006.