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The bones of birds are lighter in weight than those of mammals. Some of the bones are hollow and actually act as part of the avian respiratory system. These bones, called pneumatic bones, include the skull, humerus, clavicle, keel, pelvic girdle, and lumbar and sacral vertebrae.

The urinary system or tract includes the kidneys, the ureters (tubes that connect the kidneys to the bladder), the bladder, and the urethra (the tube through which urine exits the body)