As I spend more time both bird-watching and reflecting on my experiences, I seem to fall further and further down the rabbit hole. There really is so much to learn about our feathered friends. Like what exactly are feathers, and how do they work?

All birds have feathers. The possession of feathers is one of the features that defines an animal as a bird. Feathers make up about 6-9 percent of a birds weight (on average). Birds have a lot of feathers. For example, swans have about 25,000. Plumage refers to a group or assemblage of feathers.

For most birds feathers come out of distinct tracts, like fingernail cuticles or a hair follicle. Feathers are a bit like fingernails or teeth. When they are growing they are alive, but once they are finished forming they are no longer alive. What makes feathers different is that they are not regularly renewing. Rather they are replaced all at once, usually on an annual basis, in a process known as molting. Molting also allows for seasonal coloring to be developed both for breeding and camouflage purposes. Most birds molt after they breed, but before they migrate.

Besides being a key component for flying, feathers also provide a water and sun barrier for birds. They help birds regulate their temperate and protect them from injury. Tail feathers act as rudders in the air, in the water and on the ground. But not all feathers on a bird serve the same function.

The two major types of feathers are contour feathers and down feathers. Contour (flight) feathers usually include all feathers that are visible on an adult birds back, tail and wings. Down (semi plume) feathers are hidden in the underparts of adult birds. Most baby birds are hatched with only down feathers. Other types of feathers that are only present on some birds include powder down and facial bristles, but for the purposes of keeping this simple, I am going to focus on contour and down.

Contour feathers have two parts, a spine or quill and a vane on each side. Each vane is made up of a series of barbs that form at about a 45 degree angle from the spine. The barbs in turn have a series of hooked barbules generating from them more or less perpendicular to them. The barbules for each barb hook together, creating a knit or mess pattern. The barbules can become unhooked, but are easily re-hooked by stroking the feather from bottom to tip. It is this action which we call preening.

Down feathers have a spine as well, and their barbs also project. However, they are almost perpendicular to the spine and the absence of hooks on the barbules helps to create a more fluffy structure. Their major function is insulation. Some contour feathers have barbules without hooks toward the bottom, creating a downy insulation without a full down feather.