Entrainment of circadian rhythms by sound in Passer domesticus.

The circadian locomotor rhythm of house sparrows was entrained by a sound stimulus. The birds were maintained at a constant temperature in, dim green light. The entraining agent was 4 (1/2) 12 hours of tape-recorded bird song ,played each day. Variations in the response to this stimulus have been correlated with individual variations in free-running period. This is the first clear demonstration that a biological clock can be influenced by sound stimuli.