Which type of animal is characterized by having hollow bones?

Birds are characterized by having hollow bones, a unique adaptation that helps them achieve flight. The lightweight structure of hollow bones reduces the overall body weight of the bird without compromising its strength. This is particularly important for flight, as it allows birds to be more aerodynamic and capable of sustaining the energy needed for flying.

Additionally, the hollowness is often reinforced by internal struts or beams, which provide structural integrity while keeping the bones lightweight. This adaptation is crucial for various other behaviors in birds, such as soaring, gliding, and even rapid flapping, enabling them to occupy their ecological niche effectively.

In contrast, mammals, reptiles, and amphibians have denser bones, which are better suited to their lifestyles but do not provide the same advantages for flight. For example, the weight-bearing needs of these animals typically require stronger, solid bones to support their body mass and locomotion on land or in water. Thus, the adaptation of hollow bones is a distinctive feature that sets birds apart from these other groups in the animal kingdom.