Defeating the Cuckoo Brood parasite-host interactions show ongoing antagonistic coevolution. What mediates rapid behavioral changes that do not reflect genetic change? Davies and Welbergen show that reed warblers learn from their neighbors to behave aggressively toward models of the parasitic common cuckoo. Furthermore, reed warblers seem to be predisposed to learn to respond to cuckoos as enemies: Hosts that witnessed neighbors mobbing a harmless parrot model did not increase their aggression toward a cuckoo model. Thus, birds have templates for threats, and relevant antithreat behaviors can be turned on or off depending on social experience.