Seeing is believing: information about predators influences yellowhammer behavior

Behavioral decisions based on a trade-off between foraging and vigilance or hiding require information. I studied how the amount of information about predators influenced yellowhammers' (Emberiza citrinella) foraging delay and alert perching behavior. Yellowhammers were shown a flying sparrowhawk (Accipiter nisus) silhouette, which elicited alarm calls, or a square piece of wood (control), which elicited flight calls. Yellowhammers that could not see the sparrowhawk model, but heard the alarm calls, had less complete information about the predation risk than those that actually saw the sparrowhawk. Hearing alarm calls affected the behavior of yellowhammers. Birds with less complete information about the predator exhibited alert perching more often immediately after the encounter than did birds that saw the sparrowhawk model. Also, birds that saw the sparrowhawk resumed foraging earliest, while birds that heard the alarm calls resumed foraging latest. Although there was a tendency for a significant difference in body mass between dominant and sub-dominant individuals, there was no significant difference in foraging delay. Both the foraging delay and the increase in alert perching caused lost feeding opportunities. Completeness of information and its effect on decision-making may thus affect the fitness of an animal.