Five Types of Feathers
Feathers are the distinguishing feature of birds. All birds have feathers and no other group of animals does. Feathers serve various functions and are modified in different bird groups to serve those functions.
They allow a bird to fly, using wings and tails of feathers. They streamline a bird to make it aerodynamic. They insulate a bird to protect it from heat, cold, rain, and wind. They are colored and/or patterned to provide an identity so that birds of different species can recognize one another. Feathers often distinguish between males and females and they sometimes are brightly colored or ave accoutrements that serve to attract the opposite sex or deter competitors.
Feathers may conceal a bird by allowing it to blend into the background or break up its outline.
And they protect birds against bumps and bruises as they move through woody vegetation.
We'll cover all these various aspects of feathers in other blogs. Feathers are classifed in two ways, form and function. Here we'll just look at form.
There are five types of feathers as defined by their overall structure. The first type is the contour feather - the vast majority of feathers you see when you look at a bird. In the above photo the top three and bottom two feathers are contour feathers. These have a middle shaft called a rachis with a vane of interconnected feather barbs on both sides. These feathers are strong and flexible and function both in flight and protection and indeed form the contour of the bird. Another blog discusses the functions of contour feathers.
The second type of feather is pictured in the above photo on the right and between the contour feathers. The top part is the vane, like a contour feather, but the bottom is downy - the barbs of the feather do not interconnect and just float free. These feathers are called semiplumes and they serve to fill in the spaces between the contour feathers and provide insulation as well.
Then there are down feathers (right).The barbs of down feathers do not interconnect so the feather is fluffy. Down feathers mainly function in insulation by trapping air and tend to be close to the body under the contour feathers.
Those little hairlike things you see when you pluck a chicken or a duck, after all the contour, semiplume, and downy feathers are gone- these are filoplumes (below). They are basically a feather shaft with a few barbs at the very end. Their function is basically sensory: they tell the bird the position of its feathers.
There are variations of all these feathers, particularly the contour feathers, modified for use by particular species of birds. There are plumes, crests, horns, ruffs, pinnae, ears, powder down, and in ducks, the speculum.
In another blog we'll look at the various feather patterns on a bird, the kind of thing ornithologists and birdwatchers look for to identify the sepecies.
Rictal bristles (below) are the fifth kind of feather. Like filoplumes, they are not obvious and you need to know where to look for them. They are at the rictus, the opening or gape of the mouth. Rictal bristles are present in around one third of modern bird species and vary in length and shape with barbs at the bottom or along the rachis. Emanating from the corners of the jaw at a forward angle, it was once though that they served as a net of sorts to capture insect in midair. Research has shown, however, that they more likely serve a sensory function, giving the flying bird input about speed and orientation.
