I’ve always been fascinated by birds. I suppose it is that attraction, combined with my general love of the out-of-doors, that led me to become the avid (make that obsessed) wingshooter that I am. Since I am a very avid wingshooter, I want to learn all that I can about the critters that I pursue, and that has led me to learn all that I can about feathers. For those of you that are as totally enthralled with the sport as am I, here is more than most people would ever want to know about feathers.

Feathers are made up primarily of keratin, the same protein found in hair, fingernails and scales. Birds have all three, but the feathers are what makes them birds. It is the single feature that sets the avian class apart from the others. All creatures with true feathers are birds and all birds have feathers. When set upon the mechanical marvels we call wings; they are what gives most birds the ability to fly. 

Each flight feather on the wing is called a remex, from the Greek word for oarsman. In plurality, they are called remiges. Tail feathers can also be important to flight, and each flight feather on the tail is called a rectrix, from the Greek word for helmsman. The plural is rectrices.

In addition to the remiges and rectrices, feather types consist of neossoptiles (natal down), adult down, powder down, filoplume, semiplume, bristle and contour. The stiffer feathers (remiges, rectrices and contour) are said to be pennaceous. The rest are basically all or mostly soft, and referred to as plumaceous.

Insert Illustration, figure 1 (samples of different feather types)

Basic pennaceous feather construction consists of a center support structure that runs the  length of the feather. This is called the vein or rachis. At each end of the rachis is a small opening. The proximal (closest to the body) opening is called the inferior umbilicus. The distal (farthest from the body) opening is called the superior umbilicus. The bare part of the rachis is called the quill or calumus. In the lumen (internal cavity) of the calumus you will see pulp caps, which are the remnants of pulp tissues that nourished the feather during the growth stage. These caps add structural strength in the fully developed feather.

To each side of the rachis is attached a vane. The proximal vane is always larger than the distal vane. These vanes are made up of hundreds of barbs. Each of these barbs then has smaller barbules attached to the sides. They look like a miniature version of the larger barb. Each barbule then has many hooklets, called hamuli, along the sides. These act much like Velcro, firmly tying all the feather parts together, while remaining flexible. This is a necessary trait for flight. 

Insert Illustration, figure 2 (overview/close view/very close view of flight feather)

Since the remiges are found on the wing and are the most important to flight, they are the most studied feathers on any bird. These have been divided into several groups, each serving a different purpose in staying airborne.

The largest remiges are called primaries. These are all very firmly attached to the phalanroes and carpometacarpus (the most distal few bones of the wing) by ligaments, and supported by tendinous tissue. Most of the birds I hunt have 10 primaries per wing. Other birds may have just 9, or the tenth one may be very small, even rudimentary. If present, this tenth primary is called the remicle.

The next closest group of feathers to the body, and second in size, are the secondaries. These are all attached to the ulna bone. Secondaries number from 6 to over 40 per wing, depending on wing length in relation to body size. Most North American game birds and migratory birds have 9. Many nonpasserine (nonperching) birds are missing the fifth secondary on each wing. This condition is known as diastataxis.

The closest group of wing feathers to the body are called tertials. These are all attached to the humerus bone. They close the gap between the wing proper and the body so air can’t slip through. They typically number 5 or 6 on each wing.

Each primary, secondary and tertial remex has a unique number. Both ascending and descending numbering conventions are used, but for my game birds, including ducks and geese, the descending convention is the one that is used. The way that works is, to assign the most distal primary a number based on the number of primaries to be found on that specie. That means this primary on a goose would be called P10. The next closest to the body would be P9, then P8 and so on until reaching the first secondary. At this point, the numbering reverses to an ascending convention. That means this most distal secondary is called S1, the next closest to the body then becomes S2, then S3 and so on until reaching the tertials. At this point, only the letter changes. The numbers continue to increase. Since the last secondary was S9, that means the most distal tertial would be numbered as T10. The next closest to the body would become T11, then T12 and so on.

Covering part of the dorsal (top) side of these three kinds of most important flight feathers are covert feathers. These serve to protect them and to make them more aerodynamic. Working anteriorally (toward the head or front), the first row of coverts are the called the greater coverts. They are the largest coverts. The next row is smaller and called the median coverts. The next row is even smaller and called the lesser coverts. The last several rows are very small and called the marginal coverts. The coverts over the tertials are often referred to as the scapulars.

Attached to the pollex, which is the equivalent of the bird’s thumb and also called the alula, you will find the alular quills, and above those are the alular coverts. These can be important during slow flight, like when landing or hovering, to prevent stalling out.

Insert Illustration, figure 3 (basal view of wing feathers/bones)

Insert Illustration, figure 4 (dorsal view of wing feathers)
 

Since rectrices are found on the tail, which serves as a rudder, they too can be important to flight, especially in larger birds, like ducks and geese. There are usually 12 rectrices, but some game birds, like grouse, may have a variable number, or there may even be none, like in grebes and some ratites. Because they can be important, the largest rectrices are numbered, too. Rectrices are always numbered from the center pair outward.

Insert Illustration, figure 5 (dorsal view of rectrices)

Body feathers are not as vital to flight as are remiges and rectrices, but they do help by accommodating the specialized, flight oriented biology of birds. They also decrease drag in flight, and reduce the weight to cube ratio of birds. 

Feathers are not distributed across the bird’s body evenly. They grow in patches according to the type needed at that location. Some patches have no feathers at all. This uneven distribution is called pterylosis. The patches with feathers are called the pterylae. A single patch is a pteryla. The patches without feathers are called the apterium. A single patch is an apteria.

Many feathers have become specialized in structure and/or colorization. Generally, these are used in flocking for migration, feeding, hiding from predators, territorial displays and courtship display. Displaying aids in avoiding overcrowding on breeding grounds and limiting hybridization of species.

Examples of feathers that have specialized structure would be; the tail fan of wild turkeys, Ruddy Duck and Ruffed Grouse (territory and courtship), the hood on Hooded Merganser, Wood Duck and Bufflehead (territory and courtship), and there are noisy feathers, like those on the wings of wild turkey, woodcocks and mourning doves (territory and courtship). Other feathers are extra strong, like the center tail feathers of some woodpeckers (finding food).

Examples of feathers that are specialized in color would be: the difference between the generally bright plumage of the drakes and drab plumage of hens (bright used in every aspect of bird life except predator avoidance; drab is strictly for avoiding predators).

Ever notice the iridescence of some feathers, like those on the speculum of many waterfowl? That color is not actually part of the feather. The actual feather is clear. What causes us to see color is crystallized minerals suspended in the feather structure. The crystals act like prisms, refracting white light into the colors we see. That’s why the color perceived is often different when viewed from various angles. 

Once grown, feathers are basically dead structures, subject to wear and tear. Birds replace the worn out feathers through a process called molt. Some birds molt all of their flight feathers at the same time, becoming flightless or nearly so for up to 6 weeks. Ducks and geese are examples of this, but most birds molt in a timed pattern. 

This pattern begins at certain points on the wing and tail called molt foci. In birds with multiple molt foci on each wing, the molt proceeds descendantly. In birds with a single molt focus point per wing, it typically is the point between the primary and secondary feathers, and usually progresses outwardly from there. Other molt patterns exist, like in cuckoos, which use a saltatory molt, first loosing the even numbered flight feathers, then the odd numbered ones.

Ever notice a short primary feather on a young of the year mourning dove? You can tell it’s a young of the year by the buff colored edges of the covert feathers, but you can also tell about how many days old that bird is by which primary is short, indicating it is still growing in. There is some variation in this, so don’t stake too much on it, but you can sound like you really know what you’re talking about by using the following table.

Make note that it is not an evenly timed process, slowing as it progresses. Also make note that the molt may stop entirely in the case of locally prolonged inclement weather or abnormal drought. This is the most likely cause of deviation.

Rectrices are typically lost and replaced beginning at the center point on the tail and progressing distally. Exceptions exist, like in arboreal (tree feeding) woodpeckers and sapsuckers, which lose R2 or R3 first, then progress to R6, losing R1 last. Presumably, this is because they use these center rectrices for support on the sides of the trees while feeding, so they wouldn’t want to lose them until after they get new, strong, outer tail feathers.

For comparison, ground feeding woodpeckers do not exhibit this molt pattern. In fact, they buck the norm altogether by molting distally to proximally.

Most of the hunters that I have met seem way more interested in the trigger pulling than learning about the critters at which they are shooting, so if you have found this feather information as fascinating as I did, then you also buck the norm, but you would be a person with whom I’d like to share a duck blind; give me a call. 
.