Sound repetition rate controls the duration of tonic immobility in chicks (Gallus gallus)

Tonic Immobility (TI) functions as anti-predator defense. Its duration depends on cues signaling predator proximity. One such cue includes alarm calls from conspecifics and non-conspecifics. This study aimed to determine the cue within alarm calls that controls TI duration. We induced TI in chicks (Gallus gallus) and found that their TI durations increased in the presence of adult conspecific alarm calls, non-conspecific alarm calls, and synthetic sounds made of white noise set to the repetition rate found in natural alarm calls. Moreover, chicks did not increase their TI durations when exposed to conspecific attraction calls, synthetic sounds made of white noise set to the repetition rate found in natural attraction calls, and derived sounds made of a natural alarm call lacking an internote interval. We then created: 1) sounds with white noise set to the internote interval found in natural alarm calls and the note duration found in natural attraction calls, and 2) sounds with white noise set to the internote interval found in natural attraction calls and the note duration found in natural alarm calls. Neither affected TI duration. We conclude that repetition rate acts as a salient cue that lengthens TI duration.