The ventilatory movements of the avian pelvis and tail: function of the muscles of the tail region of the pigeon (Columba livia).

We have observed that birds of several different taxa move their tails in conjunction with sound production. These observations suggested to use that tail movements might also be associated with ventilation. Since we hypothesized that rhythmic movements of the tail and pelvis will ventilate the lungs, the activities of tail, epaxial and cloacal muscles of the pigeon were examined. Electromyograms (EMGs) were recorded from these muscles while ventilation was monitored. A muscle was considered to have ventilatory activity when the EMG activity had an obvious correlation to either inspiration or expiration. To obtain further information about the correlation between muscular activity and ventilation, we induced hyperpnea by administering 5% CO2. We report that the tail muscles that function as expiratory muscles are the M. caudofemoralis, the M. pubocaudalis internus and the M. pubocaudalis externus. We refer to these as the suprapubic abdominal muscles to distinguish them from the infrapubic (ventral) abdominal muscles. These muscles depress the pelvis and the uropygium and compress the thoracoabdominal cavity. M. transversus cloacae functions as an expiratory muscle by protracting the cloaca or by reducing its compliance. Of the suprapubic muscles we studied, the only inspiratory muscle is the axial muscle, M. longissimus dorsi. M. longissimus dorsi acts at the notarial-synsacral junction to elevate the pelvis. The rocking movements of the notarial-synsacral joint appear to be important for ventilation during conditions in which the sternum is 'fixed', such as when the bird is resting on its breast. We suggest that a division of labor may exist between the infra- and suprapubic abdominal muscles during ventilation such as panting or vocalization.