Who says which animal has the hardest bones?

The red-crowned crane's skeleton is hard outside and hollow inside, and its strength is seven times that of human skeleton. Moreover, when it migrates, it is often arranged in a clever wedge shape, so that the individuals behind can make use of the airflow generated when the individuals in front flap their wings in turn to fly quickly, laboriously and persistently. The speed can reach about 40 kilometers per hour, the flying height can exceed 5400 meters, and you can sing while flying.

Red-crowned crane (scientific name: Grus japonensis), also known as crane, northeast crane and crane, is a large wading bird, named after its red crown on its head. Endangered species listed by IUCN. Red-crowned cranes are distributed in northeast China, east Mongolia, east bank of Russian Ussuri River, North Korea, South Korea and Hokkaido. They are unique to East Asia and often live in pairs or small groups, mainly feeding on fish and shrimp. Because of its elegant posture and bright colors, it has the meaning of auspiciousness, faithfulness and longevity in East Asian culture.