Nonsongbirds can produce rhythmical sounds that, at times, have been shown to be meaningful in their communication. This raises the possibility that rhythm is a separate ability that might have evolved earlier than song. We asked whether nearly completely naïve domestic chicks perceive rhythm and respond in specific ways to different rhythmic patterns. To do so, specific constituent parameters of rhythmicity were used based on the sound of a natural mother hen's cluck. The sound samples created ranged from a continuous sound to articulated rhythmic patterns of alternating strong and weak events. Chicks' reactivity to the patterns was tested over a series of sound exposure experiments by their propensity to operate a running wheel toward the acoustic source, a paradigm simulating chicks' natural affiliative response to the hen's call. Results showed that motor activity increased markedly when acoustic events were discrete (compared with continuous), and significantly when accent structure was faster (compared with slower rates). Similar to human infants, chicks showed a significant preference for pulsed over continuous patterns. Chicks also ran harder toward calls with fast strong pulsating events, suggesting that different arrangements of events in time can be differently arousing, but independently of whether the events were presented in a regular or nonregular fashion.
