Plot Summary:Cambridge ornithology professor Nick Davies helps David Attenborough explain the parasitical brood-behavior of the cuckoo. It specifically targets 20 European species (4 British, including the warbler) and lays an egg (extremely similar to the other birds) in the nest. This hatches only to kill the hosts' own offspring and steal all of the food provided, possibly by producing a fast feeding call simulating a whole brood. The study intends to understand the sharply declining species.