• Alveolus
• Avian lung outgrowth
• Bird's body feature
• Bird's buoyancy aid
• Bird's organ
• Bird's temperature regulator aid
• Hollow part of a bird
• Lung cell
• Lung compartment
• Lung feature
• Part of the lung
• Pulmonary alveolus
• Pulmonary alveolus, put simply
• Respiratory cavity