Bird skin is thin and dry. They have in their skin the same layers that we have – i.e. epidermis and the dermis.
The single most remarkable feature about their skin is – they have feathers.
Birds have between 1,000 (humming bird) and 25,000 feathers (tundra swan), depending upon the species. Larger birds have more feathers. Most of the feathers are in the head and neck region.
Feathers serve a large variety of functions – such as providing insulation from the cold, giving aerodynamic power for flight and helping in blending with the environment (camouflage). In water birds like penguins, feathers are important in swimming and in repelling water. The ear like parts jutting out of sides of an owl’s head are not the ears. They are a bunch of feathers and they help in hearing. Feathers give mechanical protection like a coat of hair gives.
Feathers are made of keratin, the same material that makes mammalian hair, horns, hooves, claws etc. Each feather grows from a structure in the bird's skin roughly comparable to a hair follicle in humans. Feathers are of six categories.
(1) Contour feathers –These are big feathers, biggest being about 5 feet – the tail feather of a peacock. http://www.boxess.com/pfeth.htm and http://www.angelfire.com/biz2/plumesnfea...
They include vaned feathers that cover the body and flight feathers of the wings and tail. They vary in shape, size and texture. They enable the birds to fly.
(2) Down feathers – These are small and have poorly developed rachis. They are downy and have no interlocking barbules. They cover the breast and belly of a bird. Down feathers provide insulation in adult bird. http://www.ummz.lsa.umich.edu/birds/Anat...
(3) Semiplumes- These have a short rachis. They are found under the contour feathers. They serve two functions viz. providing insulation and contributing to smooth body contours.
(4) Filoplumes – These have long hair like appearance. At the tip they have small barbs. There is a sensory corpuscle at the base of these feathers They provide a sense of touch.
(5) Bristles - These are stiff, slender feathers with a hairlike appearance. They are around the eyes and around corners of mouth. They serve the same purpose as the bristles in mammals do i.e. as sensory organs. They also help some birds to scoop insects out of the air.
(6) Powder-down feather - This type of feather is found only in a few birds. It grows continually and its. Tip breaks off to form a water-resistant powder.
A single feather is light but the feather coats of birds weigh two to three times as much as their bones do.
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