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Feather - Anatomy & Physiology (view source)
Revision as of 09:23, 14 July 2008
, 09:23, 14 July 2008→Feather colour
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 and 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 and 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.
===Colour mutations===
These are of two basic types:
*The genetic ability or inability to absorb, manufacture or deposit colour pigments.
*An alteration in the feather structure (usually at barbule level) creating a different reflective or absorptive light pattern.
Mutations are often the two types in combination. However, similar colour changes can also be observed due to disease or malnutrition, especially deficiencies of essential amino acids and vitamins.
Some red colouration in the appendages of birds is caused by vascularisation and not pigment disposition. The combs and wattles on chickens and in some part, the mouth colouring of baby chicks, are examples.
===Moult===
Soft keratin structures undergo constant moult and replacement in a similar fashion to mammalian skin. Feathers moult by the growth of a NEW feather causing the shedding of an old one in a similar way to that of [[Hair - Anatomy & Physiology#Hair Types|hairs of mammals]].
Moulting patterns and periods vary with:
*Age
*Species
*Sex
*Time of year
*Breeding patterns
The moult may be:
*gradual - may last many months
*dramatic - over a few weeks
*continual - e.g. powder down