View article

One hypothesized cost of foraging is an increased risk of mortality due to predation, which may result from greater conspicuousness and reduced vigilance for predators^1–5. At high prey densities, a foraging animal must compromise vigilance to overcome the 'confusion effect'^6,7 and achieve high feeding rates^8,9. The optimal tradeoff between food intake rate and predator avoidance should depend on the forager's current hunger or energy deficit, as risk of starvation is assumed to be dependent on hunger state^8,10–12. Therefore, the probability of a foraging animal being captured by a predator is expected to increase with its food deficit and food density, and thus be dependent on its current feeding rate^1,8–12. But present evidence for an increased risk of predation associated with foraging is either circumstantial^3,4,13–16, or indirect⁹. We report here the first direct evidence for a fitness-associated cost of foraging …