Why the weight of a birds feathers is more than that of its skeleton?

The weight of a bird's feathers can be greater than that of its skeleton due to the lightweight and hollow structure of many bird bones, which are adapted for flight. Feathers, while also lightweight, are composed of keratin and can accumulate in significant quantity to provide insulation, waterproofing, and aerodynamic properties. Additionally, the extensive coverage of feathers on a bird's body increases their overall mass, sometimes surpassing that of the skeletal framework. This adaptation helps birds maintain body temperature and improve their flight capabilities.