The research described in this proposal focuses upon the coordination of respiratory, vocal organ, and craniomandibular motor programs in producing the complex learned vocalizations of songbirds and parrots. Using neuroanatomical and physiological approaches, the research plan addresses five specific hypotheses: 1) that crystallized motor programs for both the respiratory and vocal organ muscle components of adult song can be modified by feedback from the periphery only if the vocalizations are learned; 2) that this sensory feedback arises from mechanoreceptive, proprioceptive, or thermal receptors in the vocal tract or respiratory system, and that auditory feedback is not necessary; 3) that compensatory motor responses after perturbations of respiratory pressure first appear during the plastic phase of song learning during the process of matching the output to a model syllable; 4) that respiratory and vocal organ motor neurons receive inputs from a common premotor source; 5) that, in achieving vocal complexity, parrots rely on increased plasticity in their respiratory and craniomandibular motor patterns to offset the limitations imposed by a simpler tracheal syrinx.