Vigilance and predator detection vary between avian species with different visual acuity and coverage

Interspecific variations in avian visual systems have been suggested to influence antipredator strategies, yet little empirical evidence exists on how morphological and ecological factors associated with visual properties can constraint predator detection. We investigated antipredator responses (predator detection probabilities and vigilance behavior) in 2 species with different visual properties (European starlings, Sturus vulgaris, have higher acuity and wider blind areas at the rear of their heads than house sparrows, Passer domesticus) in relation to distance to the predator, body posture, and head orientation. Visual acuity may affect the distance at which a predator is detected; while the size of the blind area may influence the body postures and head orientation with the highest predator detection probabilities. Distance to the decreased predator detection probabilities of house sparrows (lower acuity) but not those of European starlings. Certain body postures and head orientations, influenced both species despite the interspecific differences in visual field configuration. Times allocated to scanning were similar, but European starlings had longer head-up scan bouts likely to enhance scanning coverage, whereas house sparrows had higher head-up scan rates probably to reduce the length of interscan intervals. We discuss alternative interpretations; however, our findings suggest that sensory configurations may limit the effectiveness of some antipredator strategies under certain ecological conditions, which has implications for understanding the evolution of different behavioral mechanisms that reduce predation risk.