There are three types of feather. The most abundant and obvious are the contour feathers: these include the long, strong wing and tail feathers, but also the short feathers that cover the body and rictal bristles around the mouth. The second type are fluffy, down feathers, lying out of sight under the contour feathers close to the body. Their role is to act primarily as insulation . . . . The third type of feather is much less familiar and you are likely only to have noticed them if you have ever plucked a bird like a chicken or a pigeon. Once all the contour and down feathers have been removed, what's left are the filoplumes, fine hair-like feathers sparsely dotted over the entire body surface and always rooted close to the base of a contour feather.
Tim Birkhead, Bird Sense: What It's Like to Be a Bird (New York: Walker & Co., 2012), p. 83-84.