The past, present and future of 'cuckoos versus reed warblers'

With their landmark publication 'Cuckoos versus reed warblers: adaptations and counteradaptations' (Animal Behaviour, 1988, 36, 262-284), Davies & Brooke ushered in a new era of research on avian brood parasitism. Building on centuries of rich natural history and detailed observation of common cuckoos, Cuculus canorus, Davies & Brooke (1988) performed a set of simple but powerful experiments to understand the adaptive value of a female cuckoo's behaviour as she parasitizes a host nest. In this essay, we explore the historical backdrop against which Davies & Brooke began their field experiments in Wicken Fen. We then evaluate four conceptual innovations made by Davies & Brooke (1988) involving rejection costs, egg mimicry, frontline defences and chick discrimination, and we show how these advances have shaped research in the last 25 years. Davies & Brooke (1988) paved the way for diverse and dynamic research on avian brood parasites, and we conclude by highlighting several promising new directions for the future, namely the genomics of adaptation, sensory ecology and cognition.