It is hard to believe that adult reed warblers are unaware that the monster bird they are feeding is not their own. Perhaps they resign themselves to filling the gaping maw of the cuckoo (Cuculus canorus) chick in the absence of anything else to do, the imposter having ejected their own brood from the nest. A cuckoo lays up to 12 eggs in different nests and some resemble the eggs of the host bird.
Cuckoos are found in all continents except Antarctica. There are 136 different species and 45 of these lay their eggs in the nests of other birds. The cuckoo is declining, probably due to loss of habitat and food, as well as colder, wetter springs and summers.
