Nick Davies has been teasing apart the dark relationship between the cuckoo and the birds it tricks into bringing up its young, for more than three decades. The Professor of Behavioural Ecology at the University of Cambridge has spent more than 30 springs and summers on nearby fenland of watching, recording and crucially experimenting. Nick's studies have deployed simple yet ingenious experiments, among the reed beds where the birds nest. They have involved mock eggs, stuffed birds and miniature loudspeakers, to piece together the cuckoo's dark story. He has even swopped cuckoo chicks with blackbird nestlings in the nests of the feathered parasite's victims. No birds are harmed in his revealing tests.

Prof Davies also talks to Jim al-Khalili about the origins of his life with birds, and the revolution in animal behaviour science beginning as he began his scientific career. Ideas about the selfish gene and game theory, along with DNA fingerprint in the 1980's, transformed the research of zoologists asking 'why' questions about what animals do.

Producer: Andrew Luck-Baker.