The skeletal anatomy of a bird
All birds have the same basic skeletal structure but with different variations in size and shape depending upon species. A bird skeleton is very unique whether the bird is flightless or adapted for flight. The skeletal structure is very lightweight and can appear fragile, however, it is actually very strong and robust. Most of the longer bones of the bird’s skeleton are hollow but reinforced through a honeycombed substructure of criss-crossing for structural strength.
When birds flap their wings, it requires much strength from large muscles which need to be solidly attached to the skeleton. Flying birds have a pronounced keel or sternum, the flight muscles are attached to this. Fused bones also helps the bird to withstand the stress of taking off, flying and landing. The keel is absent in flightless birds such as Penguins, Emus and Ostriches who also have solid bones instead of hollow ones.
The leg bones of birds are the heaviest, contributing to a low centre of gravity. This gives the bird a better balance, important in both flight and bipedal (two legged) locomotion. A bird’s skeleton comprises only about 5% of its total body weight.
The internal anatomy of a bird
Bird Respiratory System
A bird’s internal anatomy, particularly its respiratory system, differs from mammals in many ways. Bird respiration is much more efficient.
- Birds do not have a diaphram like mammals which mammals use to increase and decrease their chest cavity. Instead, birds push their sternum in and out which produces the same effect.
- Breathing rate varies depending on the size of the bird. For example, a hummingbird breathes 143 times per minute while a turkey breathes 7 times per minute. This rate increases when birds are flying. The flow of air enters through the nostrils, down the trachea and into the lungs and air sacs.
- The lungs of birds are very compact and occupy much less space than the lungs of mammals. With the help of thin-walled air sacs which extend through the body cavity and even into the bones, birds can keep a continuous flow of air through the lungs.
Because birds have a beak or bill and no teeth, they do not really chew their food and therefore have a specialised digestive tract.
- When a bird eats, the food firstly travels down the esophagus and into the crop which is really just an extension of the esophagus. The food is held in the crop before it can enter the proventriculus which produces acids and enzymes to help break down the food. The food then passes into the gizzard which breaks down tough foods such as seeds and nuts.
- Did you know that the Turkey has one of the most remarkable gizzards which can breakdown the most toughest foods such as walnuts. It can even breakdown objects that the Turkey may have eaten such as steel needles and other metal objects.
- A bird’s gizzard contains keratin to make the surface rough. Keratin is a substance which makes up human hair and fingernails and is what Rhino’s horns are made off.
- When the bird’s food has been ground up in the gizzard, it travels through the intestines where nutrients are absorbed. Waste is then expelled through the cloaca.