An eagle's skeleton weighs less than half as much as its feathers.

The skeletal system of a Bald Eagle (Haliaeetus leucocephalus) is a marvel of biological engineering designed for flight. While a fully grown eagle can weigh between 3 and 6 kilograms, its skeleton typically accounts for only about 5% to 7% of its total body mass. This means the entire frame of a large eagle weighs roughly 250 to 300 grams.In contrast, an eagle possesses over 7,000 feathers that are essential for insulation, waterproofing, and aerodynamics. These feathers collectively weigh approximately 500 to 600 grams. This ratio ensures that the bird remains light enough to achieve lift while carrying the heavy muscular load required for hunting and carrying prey.The lightness of the bones is due to a process called pneumatization. Many of an eagle's bones are hollow and reinforced with internal struts known as trabeculae. These struts provide structural integrity and prevent the bones from snapping under the high G-forces experienced during steep dives or heavy lifting.Ornithologists at institutions like the Cornell Lab of Ornithology have documented that these air-filled cavities are often connected to the bird's respiratory system. This unique anatomy not only reduces weight but also assists in oxygen exchange during high-altitude flight. The result is a skeleton that is lighter than a pile of feathers but stronger than many solid-boned mammals of similar size.