Hollow bones are a unique feature found in many birds and some other animals, such as pterosaurs and certain dinosaurs. These bones are lighter than solid bones, which helps reduce the overall weight of the animal, making it easier for them to fly. The hollow structure is reinforced with internal struts, providing strength while maintaining a lightweight design. The hollow bone structure is an adaptation that supports flight by allowing for greater mobility and energy efficiency. This evolutionary trait is crucial for birds like eagles and sparrows, enabling them to soar through the air with agility and speed.