Home Adaptations Skeletal System

Bare Bones

Bird skeleton

A bird's skeleton is similar to yours in some ways – it has a skull and legs and other features yours has – but it also has some important and very useful differences.

For example, the total number of bones in a bird's body is lower than for mammals or reptiles. That comes in handy when a bird wants to take to the air.

The bird skeleton is extremely lightweight, but strong enough to withstand the stresses that a bird experiences when taking off, flying, and landing. The bird's hollow bones make the skeleton lighter for flying, and allow more oxygen to be absorbed from the air into the blood for that extra energy a bird needs.

Bird bones usually contain air. Many bird bones are hollow, with struts or trusses (cross walls) that crisscross for structural strength. Some flightless birds – like penguins – have only solid bones, however.

Bird skull bones have air cavities that are continuous with the nasal cavities.

Trunk bones – including the vertebrae, breastbone and pelvic bones – also contain air sacs invading from the lungs. These are all called pneumatic bones.

The number of hollow bones in a bird's body will vary from species to species, though large gliding and soaring birds tend to have the most.

Birds have more neck (cervical) vertebrae (back bones) than many other animals. Most birds have 13 to 25 of these very flexible bones. Thanks to this bone structure, birds are better able groom their feathers.

Buff-breasted Sandpiper preening (Courtesy NEBRASKAland Magazine/NGPC)

Birds are the only vertebrate animals to have a fused collarbone (the furcula or wishbone). They're also the only vertebrate animals to a have a keeled breastbone – a breastbone that's long and has a structure on it shaped like a ship's keel.

A ship's keel runs from the front of a ship to the back and the ship's entire framework attaches to it. The keel part of a bird's breastbone extends outward from the top of the bone and down the breast area and acts as an anchor for a bird's strong wing muscles. The keel is a feature of strong flying or swimming birds.

Most birds have only four toes. Some have only three. The ostrich has just two toes. Most perching birds have four toes, with three that point forward and one that points back. However a few groups – including cuckoos, cockatoos and parrots, and owls, clutch the branch with two toes forward and two back.

Here are a few more fun facts to bone up on:

• In most cases, a bird's entire skeleton weighs less than all of its plumage – and you know how light feathers are!
• Birds have knees. They're often under the feathers and not easily visible. A bird's knees bend the same way your knees bend. The part of a bird's leg that you see bending backwards when the bird walks is its ankle.
• On an owl's foot, the outer toe is reversible so that the owl can perch in the usual owl way, with two toes forward and two back, or it can perch as perching birds do, with three toes forward and one toe back. The owl also uses its versatile outer toe to get a better grip on its prey.
• Bird fossils are rare because bird bones are hollow and fragile.