Paul Hobson / Reed warbler (Acrocephalus scirpaceus) perched on stem in morning light. Sheffield, England, UK. May.

Tomasz Zawadzki/ BIA / Great Reed-Warbler (Acrocephalus arundinaceus) calling, Poland

David Tipling / Cuckoo (Cuculus canorus) 12 day old chick in Reed Warblers (Acrocephalus scirpaceus) nest, Norfolk, England, UK. May.

David Perpinan / Sedge warbler (Acrocephalus schoenobaenus) singing. Scotland, UK, July.

Matthew Maran / Reed warbler (Acrocephalus scirpaceus) being released after ringing, reedbeds on the Otter Estuary, Devon, England, UK, May.

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.

Mathias Schaef/ BIA / Great Reed-Warbler (Acrocephalus arundinaceus) male calling, Vienna, Austria

Mathias Schaef/ BIA / Great Reed-Warbler (Acrocephalus arundinaceus) male calling, Vienna, Austria