Original by Dr Margaret Rowe, 2002
Last revised by the Department of the Environment and Heritage, December 2004
ISBN 0 6425 4820 X
Birds obtain water in three ways: gaining it from their food, drinking water and from some of the chemical processes that take place in their bodies.
Birds economise on water by removing wastes from their bodies in semi-solid form. For example, wastes containing nitrogen are removed in a paste containing uric acid. By contrast, mammals use over 20 times as much water to remove the same amount of nitrogen containing waste in the form of urine.
Birds which inhabit salt water and eat seafood have a problem as they take in food and water that is about 3% salt while their body fluids contain only about 1% salt. They must get rid of salt somehow and their kidneys are unable to do it. Many of them have salt glands within their nasal passages. Salt glands remove salt from the bird in a 5% salt solution. Drops of the solution run down the bill and drip off.
Birds have very efficient, 'high performance' hearts. The heart of a bird is similar to that of a mammal. Blood returning from the head and body to the heart is pumped to the lungs. In the lungs it picks up a new supply of oxygen. Blood returning from the lungs, is pumped throughout the body. The blood carries food and oxygen to all parts of the body and removes waste products including carbon dioxide.
Find a reference book that shows the path taken by blood as it flows around the body and to the lungs (humans and birds are similar).
- Which chamber of the heart pumps blood to the lungs?
- Which chamber pumps blood to the head and body?
Air is breathed in and carried through the lungs in millions of very tiny, fine tubes which are inter-woven with tiny blood capillaries. Here oxygen diffuses from the air into the bird's blood. The blood carries the oxygen to all parts of the body. At the same time, carbon dioxide diffuses from the bird's body tissues into the blood; then from the blood into the air and is breathed out.
Air-flow through the lungs of birds is very efficient—more efficient than that of mammals. This assists birds to get enough oxygen, even when flying at high altitudes. In addition to lungs, birds have a number of air sacs that are connected to their lungs. Most birds have 9 air sacs, while shorebirds have 12.
Air moves through the bird in two stages.The bird needs to breathe in and out twice for one intake of air to pass through its body. Air is breathed in and passes along tubes into air sacs in the bird's abdomen. As the bird breathes out, this air moves into the lungs. As the bird breathes in again, this air passes into a second set of air sacs.When the bird breathes out again, it passes out to the atmosphere. All air passes completely through the lungs once.These four steps are illustrated in Fig 10.White shows the position of the one intake of air.
Our lungs are not as efficient as birds' lungs.
- Find out and explain how we move air over the surface of our lungs.
Figure 10 How a bird breathes