Reliability of public information: predators provide more information about risk than conspecifics

Abstract

Animals may acquire information about predatory threats via direct cues, clues from the predator, or indirect cues from predator-elicited alarm signals from conspecifics. Although direct detection of a predator is assumed to be a better indicator of risk, only three previous studies have directly contrasted the relative information content of conspecific alarm calls to predator sounds. Studied species typically reacted equally or stronger to conspecific alarm calls than to predator sounds, suggesting that an indirect cue may be a more reliable indicator of risk. We studied zenaida doves’, Zenaida aurita, responsiveness to predator sounds and conspecific alarm signals. When flushed, zenaida doves produced voluntary mechanical wing whistles, which we predicted to be alarm signals. Observing responses to wing flap playbacks with and without whistles, we found that doves increased vigilance significantly more to wing whistles than to wing flaps without whistles or control playbacks. These results indicate that conspecifics interpret wing whistles as alarm signals. We then conducted another playback experiment, which demonstrated that red-tailed hawk, Buteo jamaicensis, playbacks elicited higher levels of dove vigilance than conspecific wing whistles. Contrary to other species, zenaida doves seemingly consider predator vocalizations more informative than conspecific alarm signals. Therefore, the reliability of acoustic signals associated with predation risk may strongly influence prey responsiveness to direct and indirect cues.