INSPIRATORY MUSCLE-ACTIVITY DURING BIRD SONG

The apparently continuous flow of bird song is in reality punctuated b y brief periods of silence during which there are short inspirations c alled minibreaths. To determine whether these minibreaths are accompan ied, and thus perhaps caused, by activity in inspiratory muscles, elec tromyographic (EMG) activity was recorded in M, scalenus in zebra finc hes and in M, scalenus and Mm, levatores costarum in cowbirds, togethe r with EMGs from the abdominal expiratory muscles, air sac pressure an d tracheal airflow. EMG activity in Mm, scalenus and levatores costaru m consistently preceded the onset of negative air sac pressure by simi lar to 11 ms during both quiet respiration and singing in both species . The electrical activity of these two muscles was very similar. Compa red with during quiet respiration, the amplitude of inspiratory muscle EMG during singing was increased between five- and 12-fold and its du ration was decreased from >200 ms to on average 41 ms during minibreat hs, again for both species, but inspiratory muscle activity did not ov erlap with that of the expiratory muscles. Thus, there was no indicati on that the inspiratory muscles acted either to shorten the duration o f expiration or to reduce the expiratory effort as might occur if both expiratory and inspiratory muscles were simultaneously active. Inspir atory and expiratory muscle activities were highly stereotyped during song to the extent that together, they defined the temporal pattern of the songs and song types of individual birds. (C) 1998 John Wiley & S ons, Inc.