Nature Watch, with Ron Freethy
FOLLOWING the breeding season, birds lose their splendidly colourful plumage as their feathers wear out.
They have to undergo the equivalent of a car's major service and worn out parts have to be replaced.
The process of replacing the feathers is known as the moult.
During the moult birds face two main dangers.
As the old feathers fall out birds are very vulnerable to cold, wet weather because it is the feathers which insulate their body.
The main danger, however, is when the loss of feathers makes flight either impossible or much less efficient because they are more easily caught by their enemies.
Wildfowl tend to lose all their flight feathers at once.
They therefore moult early when the young cannot fly either and so the family stay together with the larger more powerful adults protecting the young.
Swans seem to have developed the intelligent plan of the two parents moulting at different times so that at least one of them can chase off intruders.
The male swan is called the cob and the female is called the pen. In the old days the moulted feathers were collected and used to make quills for writing.
This is how we get the name "pen".
A penknife was made to sharpen the quill.
Song birds moult differently to wildfowl and the flight feathers are moulted gradually so that some power of flight is retained.
In late July and August, however, these birds look very untidy.
They don't feel happy enough or well enough to sing properly and they tend to hide away in cover.
At least there is plenty of food available at this time for them to make good the calcium and other minerals lost during the moult.
The new feathers are usually coated in a layer of wax which makes the new plumage look dull.
During the autumn and winter the wax gradually wears away to produce the glorious colours so typical of spring.
Scientists have found that each species of bird will moult its flight feathers in the same order each year.
Nature never leaves anything to chance.
A very definite sequence has been evolved over many thousands of years.
Practice, it seems, makes perfect.
Converted for the new archive on 14 July 2000. Some images and formatting may have been lost in the conversion.
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