Spotted sandpipers, Actitis macularia, were presented with a series of experimental tape playbacks in a natural situation in order to ascertain functional components of their song. Visible responses of individuals were used as the criterion of a given tape's ability to elicit an aggressive or reproductive response. Tapes are listed in order of response eliciting strength: normal; 3 X interval, io-note; 4.00 kHz filtered; 3 X interval, 7-note; 3.15 kHz filtered tape; and backward. Lack of response to backward tape playbacks shows that figure integrity (proper temporal ordering of frequencies) is an essential feature for song recognition in spotted sandpipers. Songs with lengthened internote intervals or decreased numbers of notes elicited fewer responses than the normal tape; however, merely increasing internote intervals decreased responses very little. This indicates that number of notes and/or sequence length is important in stimulating aggressive motivation in spotted sandpipers. Response to both the 3.15 and 4.00 kHz filtered tapes indicates that lower frequencies are essential to elicit aggression. Responses indicative of low aggressive arousal were evoked by these tapes. There was somewhat higher response to the 4.00 kHz filtered tape to the 3.15 kHz filtered tape, probably due to emphasis on the higher frequencies in the former.