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The direct relationship between predator and prey is obvious: one kills and the other is killed. But how does fear itself influence prey? By excluding predators from a population of wild song sparrows and replacing them with recorded sounds of predators, Zanette et al. show that the perceived risk of predation is powerful enough to affect wildlife population dynamics, for example by increasing the amount of time individuals spend being vigilant and reducing their time out in the open. The overall effect is to significantly decrease offspring production and survival rate. Author Liana Zanette narrates this demonstration of the work.