Who doesn’t know the story: The Cuckoo (Cuculus canorus/Koekoek) is a brood parasite which lays its eggs in the nests of other birds, particularly of Dunnocks (Prunella modularis/Heggemus), Meadow Pipits (Anthus pratensis/Graspieper), and Reed Warblers (Acrocephalus scirpaceus/Kleine Karakiet). At the appropriate moment, the hen Cuckoo flies down to the host’s nest, pushes one egg out, lays an egg and flies off. The whole process takes about 10 seconds. A female may visit up to 50 nests during a breeding season!
In this case the stepparents were Meadow Pipits, when they flew over the young Cuckoo automatically opened its mouth, eager for food.
* Canon EOS 5D Mark II with 500mm/f4 IS; ISO-400, f7.1, 1/320s; from tripod.