The origin and early evolution of birds. Air sacs in theropod dinosaurs and pneumaticity of bones in birds. Before there is a lung: the structure and function of the avian eggshell. Structure of the avian hyoid suspension and the kinetic larynx of some birds for vocalization. Evolution of the avian-like breathing mechanisms. Continuous and unidirectional air flow in the reptilian- and the avian lungs: evolutionary and functional implications. Functional specializations of the avian pulmonary circulation. Development of the airways and vasculature in the lungs of birds.

Molecular aspects of the development of the avian lung and air sacs. Functional morphology of the adult avian lung. Structure of the air sacs of the avian respiratory system. Cellular defenses of the avian respiratory system. Flight mechanics, energetics and metabolism in birds. Bird flight at high altitude. Conclusions: current understanding of the biology of the avian respiratory system unresolved matters and future directions.