Changes

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==Introduction==

==Introduction==

Feathers are one of the epidermal growths that form the distinctive outer covering, or '''plumage''' of birds.  They are the outstanding characteristic that distinguishes the Class '''Aves''' from all other living groups.  Feathers are grouped into feather ''tracts''.

Feathers are one of the epidermal growths that form the distinctive outer covering, or '''plumage''' of birds.  They are the outstanding characteristic that distinguishes the Class '''Aves''' from all other living groups.   

==Structure & Function==

==Structure & Function==

<br/>1. Vane<br/>2. Rachis<br/>3. Barb<br/>4. Afterfeather<br/>5. Calamus]]

<br/>1. Vane<br/>2. Rachis<br/>3. Barb<br/>4. Afterfeather<br/>5. Calamus]]

In most birds, the body is divided into areas that contain feather tracts, '''pterylae''' and areas that do not, '''apteriae'''.  The location and the number of tracts varies between species.  By originating from tracts rather than being randomly distributed, feathers can smoothly overlap and conform to the natural contours of the body.  By laying feathers over apteriae, air can be trapped beneath, providing insulation.

In most birds, the body is divided into areas that contain feather ''tracts'', '''pterylae''' and areas that do not, '''apteriae'''.  The location and the number of tracts varies between species.  By originating from tracts rather than being randomly distributed, feathers can smoothly overlap and conform to the natural contours of the body.  By laying feathers over apteriae, air can be trapped beneath, providing insulation.

The portions of the feather can be described as follows:

The portions of the feather can be described as follows:

*'''Biochromes''':  

*'''Biochromes''':  

Colour pigments that are deposited at the time of feather development.  These can be naturally occurring, e.g. food derived carotenoids in unaltered or modifed states, or synthetically produced, e.g. melanins (browns, greens and black).

Colour pigments that are deposited at the time of feather development.  These can be naturally occurring, or synthetically produced. Black, brown and grey colours come from melanin, whereas carotenoids in the diet create red, orange and yellow and porphyrins synthesised by the bird form green, red and some browns.

*'''Structural properties''':

*'''Structural properties''':

These structural features of the feather can be inherent in the development of the feather.  They can also be induced by materials that are placed on the feathers after development, that alter the absorption or reflection of light.

These structural features of the feather can be inherent in the development of the feather.  They can also be induced by materials that are placed on the feathers after development, that alter the absorption or reflection of light.

If a feather reflects all light, it appears white; if it absorbs all wavelengths, it appears black.  The capacity of the barbs and barbules to scatter and reflect varying wavelengths of light causes an irridescent glow of the feathers.  Blue colours are created by the barbs interacting to reflect blue light, while allowing other wavelenghts of light to be absorbed by darker melanin granules.  Green colours may be created by pigments, or more commonly, through a combination of blue and yellow pigments.

If a feather reflects all light, it appears white; if it absorbs all wavelengths, it appears black.  The capacity of the barbs and barbules to scatter and reflect varying wavelengths of light causes an irridescent glow of the feathers.  Blue colours are created by the barbs interacting to reflect blue light, while allowing other wavelengths of light to be absorbed by darker melanin granules.  Green colours may be created by pigments, or more commonly, through a combination of blue and yellow pigments.

===Colour mutations===

===Colour mutations===

*Species

*Species

*Sex

*Sex

*Time of year

*Time of year (including temperature and hours of light)

*Breeding patterns

*Breeding patterns

The moult may be:  

The moult may be: