Avian Skeletal System – The Bones of The Bird

All animals have skeletons of some type, be it an endoskeleton, exoskeleton or a completely unique one!!!! While chickens skeletons may look akin to all the rest, their are subtle differences. Their skeletons are built like birds skeletons, modified for flying (even though modern chickens dont fly!). So how is the avian skeleton different?

The tail consists mostly of feathers. In fact, its only bone is a few very small bones, fused together to form the pygostyle. The head has also been made smaller than in other animals, to allow for good balance while flying. Chickens sternums are also flat, yet light to provide anchorage for the main flight muscles. The ribcage has a structure called the uncinate process. This is seen as flaps which overlay the ribs and attach one rib to its neighbour. This provides support and extra strength to the ribcage and ensures that it does not collapse during flight.

The entire body is very rigid. The spinal processes are fused to help with flight, the ribs are fused etcetera, so acces to food is hard. For this reason, the neck is long! It also help to protect the bird from jarring the brain as it lands.

The skull, sternum and some of the vertebrae are pneumatic bones. This means that they are part of the respiratory system, in fact, they are hollow and contain air sacs. Another type of modified avian bone is medullary bones. These are those such as the tibia, ulna, toes, pubic bone and others, and provide an important source of calcium which is used when the hen is laying. In fact, a hen uses 47% of her calcium store to create an eggshell. Commercial laying hens cannot get enough calcium from diet alone, and rely on this vital store to avoid thin, or non existent egg shells.


Chicken bones are similar, yet different. The tail is fused, yet articulating, the neck is also movable, but the remaining vertebrae are fused. Some bones, especially the sternum, are large and flat to provide a hold for flight muscles.

There are two main types of bone. The pneumatic bones have air sacs in them to help flight, and act as a part of the respiratory system. Medullary bones provide an extra, and essential calcium store.