Fascinating Feathers – Structure, Function and Care
Feathers are composed primarily of a protein called beta (β) keratin. Keratin proteins are found in the skin, scales, and hair of many animals. However, there are structural variations among different types of keratin. The β keratin molecules found in bird feathers are shaped like pleated sheets while the alpha (α) keratin molecules found in mammal skin and hair are helix (spiral) shaped. However, bird β keratin is quite similar to the β keratin found in reptile skin. β keratin is also found in bird claws, scales, and beaks, but the β keratin found in feathers is more elastic than other types of β keratin.
Mature feathers lack a blood supply and are therefore ‘dead’ structures that cannot be naturally repaired if damaged. Newly-growing feathers, however, are living structures with a blood supply, and as such are sometimes referred to as “blood feathers.” However, as a growing feather matures, the blood supply in it will start to recede. In large, shed parrot feathers, it is frequently possible to see remnants of the blood vessels that supplied the feather with blood as it was growing. These remnants (called ‘pulp caps’) will be present as thin bands that stretch across the inside of the hollow shaft of the feather.
New, growing feathers are coated in a waxy sheath that will flake off as the feather matures. Birds remove these sheaths by preening, but because birds cannot preen their own heads, single birds that do not have a partner to preen them may retain the sheaths on their head feathers a little longer than normal. Many parrot owners will preen pin feathers on their birds’ heads, but only do this when the sheaths are dry and flake off easily.
As feathers can become worn through daily wear and tear, they are molted and regrown at periodic intervals. As parrots kept in captivity will experience different patterns of light and dark and may be fed different diets, the timing of the molt can vary among captive parrots. A parrot that has not undergone a molt for a long time (i.e. over a year) may have quite a bit of damage on the tips of its feathers. There may also be some black or brownish marks on the feathers, especially at the tips.
As feathers are made primarily of protein, parrots need sufficient protein in their diets to grow strong, healthy feathers. Pelleted diets generally contain sufficient protein (and amino acids), as can mixtures of grains, cooked beans, peas, quinoa and corn.
Most of the feathers that are visible on an adult parrot are contour feathers. These include the tail feathers (also called “remiges”), the flight feathers (also called “retrices”), and the outer (visible and usually coloured) feathers on the head and body. The contour feathers have several functions. The flight feathers allow the bird to fly and the tail feathers help the bird control its flight path. Contour feathers also provide some insulation and waterproofing, protect the body from dust and debris, and can play an important role in communication. For example, cockatoos have erectile crests on their heads that they can raise and lower in order to express anger, surprise, or excitement. Hawk-headed parrots also have a ‘headdress’ of feathers on their heads they can erect. Even parrots without such specialized feathers can erect the contour feathers on their heads and napes if agitated or alarmed. Additionally, many parrots will fan out their tail feathers if alarmed or excited.
Contour feathers are the most structurally complex feathers on a parrot. They are composed of a long, central shaft that has a flat ‘vane’ on either side, except at the base. The base of the central shaft is hollow and will lack a vane. This part of the shaft is called the ‘calamus.’ The upper part of the central shaft, which has a vane on both sides, is called the rachis.
If you take a shed feather and pull the vane apart, you will see that there are many thin, hair-like structures branching off of the rachis. These are called barbs. Many contour feathers have two types of barbs, which are called plumulaceous barbs and pennaceous barbs. Plumulaceous barbs are located near the base of the feather and are white, loose, and soft. Some flight feathers have few or no plumulaceous barbs. Pennaceous barbs are located above the plumulaceous barbs and are firmer. In the pictures of blue and gold macaw feathers accompanying this article, the pennaceous bars are blue.
The structure of pennaceous barbs is quite complex. Each barb will have a central shaft called a ramus. Each ramus will then have two rows of structures branching off of them called barbules. These will appear as ‘fuzz’ on the ramus to the naked eye. The ends of the barbules on one side may be covered in little hooks called barbicels. The barbicels can neatly wrap around the barbules on the barbs above. When all of these little hooks are wrapped around the barbules above them, the feather will have a very smooth and neat appearance. However, when a bird goes about its daily activities, the hooks can become dislodged from the barbules.
Birds can restore the structure of their feathers by preening. When preening, a bird will run his feathers through his beak and this will rehook the barbs on the feathers back together. You can try this with a shed contour feather – pull the barbs apart and see if you can “zip” them back together with your fingers.
Remiges and Retrices
The remiges (tail feathers) and retrices (flight feathers) are the largest and stiffest feathers on a parrot and they provide little insulation but are critical for flight. They differ from other feathers in that they are generally attached to bones, instead of being anchored in the skin.
The primary flight feathers (the flight feathers at the end of the wing) provide forward thrust when a bird flaps its wings downward. These feathers are attached to a bird’s manus (‘hand’) bones and the bones of its second digit. Parrots have ten primary feathers. The secondary flight feathers are also critical for flight and they help provide a great deal of lift. These feathers attach to the ulna (“arm bone”) of the wing. Most parrots will have ten secondary feathers but this number varies from 8-14.
The primary and secondary flight feathers differ from contour feathers on the body in being asymmetrical, as the leading vane will be narrower than the trailing vane. Both primaries and secondaries are asymmetrical, but the primary flight feathers are typically longer and more pointed than the secondary flight feathers.
Parrots have twelve retrices (tail flight feathers), which also have asymmetrical vanes. The central retrices are attached to the tail bone (pygostyle). Tail feathers play an important role in steering and braking.
Underneath the contour feathers are down feathers. They provide lightweight and effective insulation and they are white and have a simpler structure than contour feathers. They either lack a central rachis, or have a very short one. If there is a rachis, the barbs will be much longer than it. The barbs can have small projections on them, but they do not hook together the way pennaceous barbs on a contour feather can.
Cockatoos, African gray parrots, and Mealy Amazons also produce large numbers of specialized down feathers called powder down feathers. A few other groups of birds, including herons, also produce powder down feathers. The barbs of powder down feathers slowly disintegrate over time and produce a white talcum-like powder that will coat the bird’s feathers. Unlike other types of feather, powder down feathers grow continuously and are not molted.
There are feathers that appear to be intermediate between a down and a contour feather. These are called semiplumes. Unlike down feathers, they have a central rachis, but the barbs are white and fluffy, like the barbs on down feathers. They are usually hidden underneath the surface contour feathers and likely help with insulation.
Filoplumes and Bristles
Filoplumes are inconspicuous feathers that are hard to see and are somewhat hair-like in appearance. They are composed of a central shaft with a few short barbs at the top. They are associated with contour feathers, especially those on the wings and tail. They have a sensory function and monitor the movements of the contour feathers. When feathers associated with filoplumes move, the filoplumes move too. Because filoplumes have many sensory cells at their bases, their movement allows the bird to sense movement in his feathers.
Bristles are also simple in structure. They are short and have a central shaft with a few barbs at the base. On parrots, they are often located around the eye and nostrils where they presumably have a protective function and keep debris out.
Preening and the Preen Gland
Parrots spend a lot of time preening their feathers in order to keep them smooth and clean. A small gland just above the base of the tail also plays an important role in preening. This gland (the uropygial, or “preen” gland) secretes a mixture of chemicals, including waxes, fatty acids, fat, and water. When parrots preen, they often nibble at the preen gland (to get preen gland oil on the beak) and then rub their beaks along their feathers. That applies the preen gland oil to the feathers. They may also rub their heads against the gland and then rub their heads on the feathers.
It is not completely clear what the function of preen gland oil is (particularly in parrots), although it generally appears to help with waterproofing feathers and maintaining their elasticity. In addition, the preen gland oil of chickens contains vitamin D precursors, and many books and articles on birds state that when ultraviolet light hits these precursors after they are spread on feathers, they are converted to vitamin D, which the bird can then ingest as it preens. Thus, preen gland oil may provide a vitamin D supplement. However, some parrots, including Amazons and Hyacinth Macaws, lack preen glands but do not generally suffer from vitamin D deficiencies.
Parrots preen themselves to maintain the integrity of their feathers, and they also need baths or showers to keep their feathers clean and healthy. Some birds prefer showers, and such birds should be sprayed with water a few times per week. Others may prefer to bath, and such birds should be offered bowls of water for bathing purposes. If a parrot really enjoys water, it’s fine to bath or shower him or her every day if desired.