Feathers, flyways and fast food
Original by Dr Margaret Rowe, 2002
Last revised by the Department of the Environment and Heritage, December 2004
ISBN 0 6425 4820 X
Five senses, or more?
Considering the size of their body, birds have large brains. The parts of the brain that deal with messages from the eyes and from the parts of the ear and body that detect balance are especially large. These two senses are very important for birds.
Excellent vision is very important to the survival of birds. The eyeballs of birds are relatively large. Birds can focus very sharply on the whole visual field at the same time, detect movement and, most birds, detect colour vividly. Birds have little ability to move their eye-balls and make for this by moving their whole head.
Birds with eyes close together, like owls, can judge close distances very accurately, using the three-dimensional vision resulting from overlap of the images received by the two eyes. In most birds, the eyes are so widely apart, and towards the sides of the head, that there is not much overlap of the images received from the two This results in vision over a wide field, but their sight is largely two-dimensional. Many of these birds have other ways of estimating distances. Some cock their heads while viewing prey, judging distances by viewing it from different angles.
Birds have a third eyelid. It is clear and has its own lubricating gland. It passes over the eye like the windscreen wiper of a car. It provides good protection from wind during flight.
Birds have an excellent sense of balance and fairly good hearing.They also have good senses of taste, smell and touch.
This is not fully understood. The birds have an inbuilt compass. It has been shown that some species of birds can observe the direction of the sun's rays and use these as a compass. Others use patterns of stars to orient themselves towards the north or south. Some birds have tiny crystals of magnetite, which act as tiny compass needles, in their heads. These compass needles align with the earth's magnetic field and help the birds set the directions of their flights.
The bird's internal clock, indicating the time of day, is also needed so that the bird can account for changes in the position of the sun and stars over the 24-hour period. Other methods used include detecting wave patterns and the use of other senses such as sound and smell. It is likely that some birds use combinations of these methods.
When migrating south to their wintering grounds, shorebirds usually return to the same site each year. They use familiar landmarks to help them recognise their chosen site.
Birds have an inbuilt "body clock" which tells them when it is time to migrate. Hormones circulate in the birds' bodies in response
Some birds seem to have an inbuilt barometer. This allows them to detect changes in air pressure.
Birds communicate to each other by the sounds they make, by displays including postures and dances and by feather colours and patterns. They are capable of remembering and recognising each other by their voices. They can recognise familiar places. Migratory birds communicate by calling to each other as they fly.