Visual obstruction, but not moderate traffic noise, increases reliance on heterospecific alarm calls

Abstract Animals rely on both personal and social information about danger to minimize risk, yet environmental conditions constrain information. Both visual obstructions background noise can reduce detectability of predators, which may increase reliance information, such as from alarm calls. Furthermore, a combination auditory constraints might greatly because the loss one source cannot be compensated by other. Testing these possibilities requires manipulating while broadcasting We therefore experimentally tested effects barrier, traffic noise, their response Australian magpies, Cracticus tibicen, heterospecific The barrier blocked only cues, playback moderate could mask subtle acoustic cues danger, predator’s movement, but not alarm-call playback. predicted that calls would with either or constraint, there disproportionate when were present. As predicted, individuals responded more strongly was barrier. However, did affect responses, effect greater during traffic-noise conclude reduction personal, led calls, confirming indirect evidence other species. absence in magpies hearing is less important than vision detecting predators.