David Beeson, June 2022
There are three basic feather types: 1) The PRIMARY FEATHERS which provide the left in flying, 2) CONTOUR FEATHERS that often have a more downy lower part and 3) DOWN FEATHERS that are for controlling body temperature – the bird’s underwear!
Down feathers can be plucked in birds such as the wider to provide insulation within the nest. Some of these feathers break off at the tip to yield a fine powder – especially in herons.
Some parts of a bird’s body may lack feathers. The brood pouch being an example.
Obviously, feathers are not randomly spread over a bird’s body. Each type grows in specific locations.
There are feather types intermediate between contour and down feathers.
Each feather can be moved separately by muscles within the skin, even though the feather is dead at maturity.
Feathers are unique to birds, each consisting of a tapering shaft (Rachis) bearing a flexible vane on each side. The short basal part of the feather (Calamus) is round in section and is almost hollow. During growth, it has a blood supply but that is sealed off at maturity, leaving a non-metabolising structure. It is dead.
Feather numbers vary from just under 1000 in some hummingbirds, to over 25 000 in wintering swans. In most birds the feathers contribute 15 to 20% body weight.
Feathers often change colour by abrasion, with the ends being rubbed off during use. The change from winter to summer plumage is said to be often achieved in this way rather than growing new feathers which would be resource demanding.
Feather colours are produced by a combination of relatively few pigments – melanins, which the bird manufactures, and carotenoids giving the yellows and reds. The latter are from the diet. Of course, flamingoes lose their pink colour when deprived of their natural placktonic diet.
Additional colours by microscopic prisms of wax (sort of!) which refract light and generate the colours on birds such as the UK kingfisher.
Birds usually moult their feathers once a year. Golden eagles keep some of their feathers for two years.
The wish bone is equivalent to our collar bones, the clavicle.
Penguins swim with their wings, so have a keel.
Having lost their fore-limbs to flight evolution has given birds many more neck bones – 11 to 25. This gives them a flexible neck capable of reaching most parts of the body.