A feather is a growth from the skin, much like a hair, that forms the plumage of birds. It is an integral part of a bird’s biology, both physically and behaviorally. They have evolved over millions of years to be ideally adapted to benefit birds in a range of functions such as flight, insulation and protection. A range of different types of feathers work together to provide birds with the complete package and allow them to be the most successful flyers on Earth.
Uses of Feathers
Feathers are not only useful for flying but are vitally important to birds for a number of other reasons. Possibly the most important function of feathers is their role in insulation. Various layers of feathers help to keep birds warm, while their tight arrangement can form a water tight seal to again protect them from the elements.
By providing a thick buffer, they also protect the skin from cuts and scrapes and can allow birds to forage though harsh vegetation. Certain types of feathers are important in sensory functions and help with decision-making during flight as well as searching for food. Tail feathers often provide stability and in the case of male peacocks are used to entice a member of the opposite sex into courtship. Feathers have also been thought to be important for some species of birds in filtering dust from their nostrils and in scooping up food.
In general, feathers have a fairly simple anatomy; they consist of a shaft, barbs and barbules. The shaft is the long circular midrib of the feather and can be split into the rachis, which has no barbs and is the end nearest the body of the bird, and the calamus, the hollow end of the shaft.
Types of Feathers
Not all feathers are born the same and each individual bird will have a number of layers of feathers and a range of different types, each with different primary purposes. The outermost layer are known as contour feathers and they are primarily used for flight and streamlining but also insulation and protection.
Semiplume feathers sit beneath the outer layer and are mostly used for streamlining and insulation. Down feathers are found closest to the skin of a bird and are vitally important for insulation and are commonly seen on the chicks of many bird species such as ducks and chickens. Filoplumes are used as sensory tools and help a bird make adjustments during flight, a filoplume feather contains have a shaft with very few or zero barbs.
Bristles are tiny barbless feathers often found around the face of many birds and there are a range of hypotheses for the purpose of bristles. For insectivorous birds with bristles around the mouth it is thought that they provide protection from wriggly, defensive prey; owls have bristles believed to be useful in finding prey when hunting in the dark; and woodpeckers have bristles around their nostrils which are thought to filter out dust from their wood pecking activity.
Evolution of feathers
The first sign of feather evolution goes back as far as 325 million years in dinosaur fossils. These primitive feathers, however, are not believed to be associated with flight as they are simple in structure and must have been beneficial for another purpose, such as protection or warmth. Fossil records of the first complex feather useful for flying date back to around 160 million years in the Late Jurassic from fossils of coelurosaur dinosaurs.
Last edited: 15 December 2015