Colours in Birds

One of the most important features of the multicoloured feathers of birds is that they are lifeless structures. The reason why a feather maintains its colour exactly, even after it is shed, is that a fully developed feather is completely lifeless.
Rich colour diversity in birds is basically due to the presence of pigments in the feathers, which were stored during the initial development phases of the feather, or the light shifts which occur depending on the structural characteristics of the feathers.
Since these formations, which are made up of the substance keratin, are soon worn down by environmental conditions, they are regularly renewed. Yet, each time, the bird regains its colourful feathers. This is because the feathers of birds continue to grow until they fully reach the necessary length, and the characteristic colour and pattern of that specific kind.
Due to their different structure, feathers can have an appearance similar to that obtained by a glass prism breaking light into different colours. Colours that are formed through refraction of light in this way are brighter and more metallic than those that are coloured by pigments. The colours of these feathers shift from blue to green, and from orange to red. Generally, the green, blue, and metallic colours in birds are formed through the reflection and refraction of light. Yet, some of the colours of feathers come from pigments.39
There are mainly three kinds of pigments in birds. These are melanin pigments that produce black, brown or dull yellow, lipochrome pigments that produce red, yellow or orange, and carotenoids. Blue, green and some other bright colours in birds are created by microscopic bubbles in the keratin of the feathers that refract the light. The feathers absorbing the full spectrum of light and only reflecting blue, on the other hand, creates the blue colour of some birds.40
Hormones also play an important role in colour change in birds. The colour difference between the male and female members of some species is caused by sex hormones. The different colourings and feather shapes of cocks and hens, for example, depend on the oestrogen hormone. The colours of birds are important for their adaptation to their habitat as well as for male and female members' recognition of each other and the males' courtship of females in the mating season. In addition, pigments, which give colour to feathers, enhance the strength of the feathers, store energy coming from the sun and prevent harmful ultraviolet rays from entering the body