Early perceptual selectivity in the swamp sparrow.

The cardiac orienting response to species-specific songs was measured in young swamp sparrows and song sparrows. Swamp sparrows respond with significantly greater deceleration to conspecific songs than to songs of the sympatric song sparrow. This discriminatory ability is operating during the sensitive period for song learning and is evident upon initial exposures to conspecific song. These results are the 1st direct evidence for a sensory component in the process of selective vocal learning in birds.