Bence Mate / Common cuckoo chick (Cuculus canorus) begging for food from Great reed warbler (Acrocephalus arundinaceus) foster parent, Pusztaszer, Kiskunsagi National Park, Hungary

Bence Mate / Common cuckoo chick (Cuculus canorus) begging for food from Spotted flycatcher (Muscicapa striata) Pusztaszer, Kiskunsagi National Park, Hungary

David Kjaer / Cuckoo (Cuculus canorus) perched in tree. Buckinghamshire, UK, June.

David Tipling / 2020VISION / Cuckoo (Cuculus canorus) 12 day chick in Reed Warbler nest (Acrocephalus scirpaceus) fed by Reed warbler, Fenland, Norfolk, UK, May

David Tipling / 2020VISION / Reed Warbler (Acrocephalus scirpaceus) at nest feeding 12 day Cuckoo chick (Cuculus canorus), Fenland, Norfolk, UK, May

David Tipling / 2020VISION / Reed warbler (Acrocephalus scirpaceus) feeding 12 day chick of European cuckoo (Cuculus canorus) in its nest, East Anglian Fens, Norfolk, May. 2020VISION Book Plate.

David Tipling / 2020VISION / 12 day chick of European cuckoo (Cuculus canorus) in Reed warbler's (Acrocephalus scirpaceus) nest, East Anglian Fens, Norfolk, May

Andy Sands / European Cuckoo (Cuculus canorus) female perched on fence post, Isle of Coll, Scotland, UK, June

Hanne & Jens Eriksen / European cuckoo {Cuculus canorus} resting on fence on migration route, UAE, October

Stephen Dalton / Hedgesparrow / Dunnock (Prunella modularis)feeding European cuckoo (Cuculus canorus) in oak tree, UK

Andy Sands / European Cuckoo chick (Cuculus canorus) being fed by Reed Warbler on post, West Sussex, England, UK

Pete Cairns / Cuckoo (Cuculus canorus) two males fighting over territory. Cairngorms NP, Scotland, UK.