(1) They have small, rudimentary clavicles, a small procoracoid process, no syrinx , and reduced caeca.(2) That is reflected in the fact that two of the relevant taxa, parrots and songbirds, use different parts of the syrinx to make their vocal signals and different parts of their brains to control sound production.(3) They have a tracheobronchial syrinx with one pair of intrinsic muscles and modified bronchial and tracheal rings.(4) The muscles involved in the control of respiration, the syrinx , and movements of the beak are used during song, and all muscular activity requires energy.(5) But the physical part of the syrinx in small songbirds is kind of similar from one bird to the next.
