Feathers and Plumage
Have you ever seen a bird without feathers? Today, all birds have feathers and birds are the only animals with feathers. However, it would be inaccurate to use feathers as a way of defining birds. This is mostly because there were several non-bird dinosaurs that had wings. One of these was the Caudipteryx. This species had wings but they were not sufficient for flying. These extinct bird-relatives did use the feathers and plumage for many other adaptive things, such as insulation, breeding, and camouflage. We shall examine all of this and other adaptations for feathers and plumage in this section.
Types of feathers:
Bird feathers are amazingly complex. Each feather is made from the protein Keratin. While keratin also makes up snake and lizard scales, it is a slightly different compound in birds. The three main types of feathers are the filoplumes (sensory feathers), the contour feathers, and the down feathers (insulation).
One of the reasons bird feathers are so complex is that each feather is made up of many different parts. The feather is similar in many ways to a palm frond. The rachis (same as in palms) is the central core. The area that the feather attaches to the bird is called the calamus. The rachis has barbs that extend from it, which collectively make up the vane. If you’ve picked up a feather you’ll notice that at the bottom there are several ‘non-flat’ parts that are called the pennaceous section.
Along the feather, each barb has a shaft called a ramus. From each side of the ramus are barbules and barbicels. In essence they act like modern day velcro. One side can hook onto the other and keep the wing stiff. As a kid I’m sure everyone has run their fingers the wrong way down a bird feather and separated them. Birds can ‘zip-up’ their feathers by running them the other way and in essence, re-hooking the barbules and barbicels.
Down Feathers: These feathers do not have barbules on them even though they still have some of the same structure as a normal feather. They are normally very soft because they lack the stiff barbes.
(OWLS) : Some birds have modified this arrangement. Owls for instance have velvet-like projections that extend from their feathers that allow them to fly silently.
(Sand-Grouse): Sand-Grouse that live in desert locations have feathers with highly curled barbs. These barbs will hold water when a bird dips into an oasis. This allows the bird to then fly back to the nestlings and they can drink from the birds breast.
There are 10 primary feathers, connected to the hands that are used to produce thrust (labeled with roman numerals) and several secondary feathers connected to the forelimb that are used to produce lift. There are also several rows of coverts on the upper and lower wing that are arranged in-between the primary and secondary feathers.
Look at a bird and you’ll notice that their wings are overlapping. Another type of ‘bird velcro’ is the connectivity of these feathers through friction barbules. They are also on the tail feathers (known as retrices).
There are a few birds that have highly modified feathers. The following are some note able ones.
Nightjars: These birds produce a very elongated secondary flight feather that is used in breeding. It does not have aerodynamic properties and instead probably restricts their flight. After the mating season they fall off (or are bitten off).
Manikins: In the neo tropical forest, manikins form breeding leks and will often snap their feathers down, creating a very loud fire-cracker like sound. This is caused by the secondary feathers that have very large shafts.
Motmots: The tail-feathers of mot-mots are extremely elongated. These are probably used to give some sort of social signal to others of their kind.
Spatuletail Hummingbird: The Marvelous Spatuletail has a very long extended tail feather. Scientists do not know exactly what the purpose of this is. It is doubtful that there are any improvements in their flight because of it.
Honeyguides and Snipes: Their tail-feathers have a lot of space in between them. When air passes through it causes turbulence and a lot of noise.
Woodpeckers: The shafts of the tails of woodpeckers are modified for support so that when they perch on the side of trees they can brace themselves vertically.
Caprimulgiform birds (nightjars and kin): These birds have highly modified feathers that look like whiskers. They are actually just contour feathers, but are probably sensory adaptations to help them catch bugs.
Bristle-thighed curlews: These birds have modified feathers associated with the upper portion of their leg. These feathers are probably extra sensory feathers to determine the depth of water they are standing in.
How many feathers to birds have? To determine this you’d have to keep track of feathers into the thousands. When you plucked (as you would a chicken), you’d notice though that the feathers didn’t cover the bird like a grass covers your lawn. Instead there are rows (tracks) of feathers. Since the feathers overlap each other, its seems like they are all one continuous covering.
Have you ever seen a bird nosing under its tail and then stroking its plumage? The preen gland, that hold the musty oils that help cover and waterproof the feathers are found just under the tail.
Feather parasites like lice, can really do a number of the feathers. They actually eat the feathers and effect the insulation of the birds.
Ever noticed that birds don’t stay the same color? Unlike humans, they can change color through a process of changing out the feathers. New feathers start to grow through the stalk of the old ones and are then ‘molted’. The basic coloration of a bird can usually be remembered as the ‘non-breeding’ color. The alternate coloration of the bird is usually the breeding plumage. Many birds will thus molt twice a year, once to the alternate and once to the basic phase.
The colors on bird feathers are caused by a combination of the pigments and the placement of the pigments on the wings. Certain pigments like carotenoids produce yellows, and reds. Others like melanins produce the browns and grays. Blue and green plumage is very different because they have many pigments that produce them.
The placement of the pigments are important because some birds have their pigments packed on the barbs and others have them on the shaft of the feather. Thus, if you were to examine a bird that had red on the barbs, a worn bird would appear less red!
LINKS TO FEATHER INFO:
By Rob Nelson
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