Why do birds have hollow bones?

Birds have hollow bones to reduce their body weight and make flight more efficient. These lightweight bones are supported by a strong internal structure of struts and are filled with air sacs connected to the respiratory system. This adaptation allows birds to maintain the strength needed for flight while minimising energy expenditure. Additionally, the air sacs in the bones enhance oxygen exchange, supporting the high metabolic demands of flying. This unique skeletal feature is one of many evolutionary traits that enable birds to soar through the skies.