Matthew Maran / Bird ringer measuring migrant Reed warblers (Acrocephalus scirpaceus) in reedbeds, Otter Estuary, East Devon, England, UK, May.

Matthew Maran / Man ringing migrant reed warblers (Acrocephalus scirpaceus) noting down details, in reedbeds on the Otter Estuary, East Devon, England, UK, May 2017.

Matthew Maran / Ringing migrant reed warblers (Acrocephalus scirpaceus) in reedbeds on the Otter Estuary to improve understanding of their ecology and life cycle. Devon UK

Roger Powell / Sedge warbler (Acrocephalus schoenobaenus) perched in a hawthorn bush. Druridge Bay, Northumberland, England, UK, July.

Roger Powell / Sedge warbler (Acrocephalus schoenobaenus) perched in a hawthorn bush. Druridge Bay, Northumberland, England, UK, July.

David Kjaer / Sedge Warbler (Acrocephalus schoenobaenus) Greylake RSPB Reserve, Somerset Levels, England, UK, August.

David Kjaer / Sedge warbler (Acrocephalus schoenobaenus) singing, Greylake RSPB Reserve, Somerset Levels, England, UK, May.

David Kjaer / Sedge warbler (Acrocephalus schoenobaenus) singing, Greylake RSPB Reserve, Somerset Levels, England, UK, May.

David Kjaer / Reed warbler (Acrocephalus scirpaceus) with insect larvae in beak, Greylake RSPB Reserve, Somerset Levels, England, UK, June.

David Kjaer / Reed warbler (Acrocephalus scirpaceus) Greylake RSPB Reserve, Somerset Levels, England, UK, June.

Brian Bevan / Close-up of a pair of Reed warblers (Acrocephalus scirpaceus) feeding young at nest, Bedfordshire, England, UK, July.

Brian Bevan / Pair of Reed warblers (Acrocephalus scirpaceus) feeding young at nest, Bedfordshire, England, UK, July.