Molting is catastrophic and lasts about 10 days. Can swim 30 miles an hour. Agile in water. Mouth and tongue have backward- pointed spines to hold fish. Feet are webbed and serve as a rudder.
Feet also have claws at end for climbing.
Skeleton is similar to flying birds. Large keel attaches muscles. Wings are flattened like oars. Bones are solid and act as ballast while diving.