Feather Anatomy
On the left is a typical contour feather from a Barn Owl (Tyto alba) . This happens to be a primary wing feather, located on the outer part of a wing. The major part is the calamus or quill, the naked bottom of the feather, which attaches to the skin and extends into the rachis, the backbone of the feather.
On both sides of the rachis are the vanes, the interconnected barbs that form the bulk of the feather, divided into posterior and anterior portions. The vane is made of pennaceous barbs, barbs with interlocking barbules that form a coherent vane. At the bottom are plumulaceous barbs, barbs without interlocking barbules, forming a loose fluffy layer at the base of a contour feather; or making up the entirety of a down feather.
Contour feathers with their flexible vanes are found on the wing and the tail for flight and over the body for aerodynamics and weather proofing. The notch indicates it was from an outer wing (primary) feather. Inner wing or secondary feathers have no notch. Graphic from USFWS Feather Atlas.
A closeup view of a vane of a white dove feather shows the barbs separated, as you might do by running your thumb and forefinger down along the vane. You can see the rachis on the right and the parallel barbs extending leftward and upward.
You can see some small serrations on the barb to the left of the gap; these are the barbules. Click to enlarge.
On the right above is a microscopic view of the barbules on the separated barbs.
Below is a diagram of a barb with its subdivisions, the barbules. On the barbules are hooklets. The hooklets hook onot adjacent barbules to tie adjacnt barbs together much like velcro.
Click on the diagrams to enlarge them.
Down feathers (right) are found close to the body and are very soft and fluffy because they do not have a rachis or barbules. This means their barbs are free to move around, giving them that fluffy appearance while trapping air and providing insulation for the bird.
There is a specialized kind of down call "powder down." Powder down occurs in a few groups of birds. such as herons and egrets. The tips of the barbules on powder down feathers disintegrate, forming fine particles of keratin, which appear as a powder, or "feather dust", among the feathers. The bird uses these keratin particles along with body oil to preen and waterproof their feathers.
Semiplumes (far right) are plumulaceous on the bottom and pennaceous on the top (the proportions vary) and serve to fill interstices between the contour feathers on the body.
Click on the diagrams to enlarge them.
