Birds are the only animals on our planet to have feathers. Feathers evolved from reptilian scales and even today, birds still have scales on the lower parts of their legs and feet. Their are many different types of feathers that come in all sorts of shapes, sizes and colours. Some feathers, particularly female bird feathers, are dull in colour for the specific reasons of safety and camouflage while male bird feathers are generally colourful for the purpose of displaying and for finding a mate.
Below is a prime example of the differences between male and female birds. The male duck on the left is by far more colourful in appearance than the duller-coloured female on the right.
Birds have feathers which are made from tough fibrous protein keratin, a protein which is also used to make horn and hair by different animals and also beaks of birds.
Feathers have many different functions apart from helping the bird to fly or swim. They are used for protection, insulation, waterproofing, camouflage, communication and display.
Feathers grow quite quickly on birds and are sealed off at the base. Fully developed feathers become ‘dead matter’ just like the finger nails of a human being, however, they are still attached to muscles at the base of each feather which can move the individual feathers and keep them in place.
Feathers grow from the epidermis of the bird’s skin. Feathers typically have a long, hollow shaft, also called the ‘quill’ or ‘rachis’ which supports the large, flat surafce, the ‘vane’. The vane is made up of small parallel strips called barbs which are like the teeth of a comb. Barbs bear even smaller branches called barbules, some of which are interlocking hooks. If you ever seen a bird nosing under its tail and then stroking its plumage, it is preening itself. Preen glands contain musty oils that help cover and waterproof the bird’s feathers and are located just under the tail. When a bird preens, it arranges the barbs into neat rows to form an airproof surface which is essential for efficient flight and insulation.
Birds have different types of feathers on different parts of their bodies.
- Flight feathers or remiges, include primary feathers and are located towards the wing tips. These feathers can spread out like vanes of a fan and are therefore referred to as pennaceous feathers or vaned feathers.
- On the inner wings are secondary flight feathers which run along the ‘arm’ of the wing and sustain the bird in the air, giving it lift. The number of secondary feathers varies a great deal among bird species. Birds that perch have 9 or 10 secondary feathers, but some bird species have as many as 20 secondary feathers. Further inwards on the wing are the secondary wing coverts and the upper marginal wing coverts which are connected to the bird’s scapulars. Further outwards on the upper wing edge are the alula and then the primary coverts which precede the primary flight feathers as described above.
- Tail feathers or retrices, can move and spread like the primary feathers. Tail feathers are used as a ‘rudder’ to steer the bird when in flight.
- Contour feathers are the outer layer of feathers that form a stream-lined surface that cover a bird’s body, wings and tail and give the bird its characteristic appearance. These are the largest feathers and defines the bird’s colour and smooth shape and includes both the flight feathers (remiges) and tail feathers (retrices). Contour feathers are very important to the bird as they provide a first level of defence against physical objects, sun, wind and rain.
- Beneath the contour feathers are soft, fluffly downy feathers. These feathers help keep the bird warm by trapping air to provide insulation.
There are 4 other main types of feather. These are Semiplumes, Filoplumes, Bristles and Powder feathers.
- Semiplumes – these feathers are located half-way between the contour feathers and down feathers. They are downy in texture, with no interlocking barbs. They help to provide insulation and a certain amount of shape to the bird.
- Filoplumes – these are hairlike feathers with a few soft barbs near the tip. They are associated with contour feathers and may be sensory or decorative in function. They provide the bird with insulation, and they may be found in both feather tracts (pterylae) and bare spaces between the feathered areas of the bird (apteria), generally in adult birds. They also form the first feather coat of most young birds.
- Bristles – these have practically no barbs at all and are like short, stiff hairs. They are located around the eyes and mouths of some birds and provide protection. They particularly occur in birds such as the Honey Buzzard (Pernis apivorus) which feeds on the nests and young of social bees and wasps. Honey Buzzards have an interesting defence adaptation for dealing with wasps and bees. Their facial feathers are very dense and contain a chemical which has sedative properties which affects insects. When the bird starts attacking a wasps nest, the occupants fly out to attack and then become docile allowing the bird to feed up on its prey. Woodpeckers also have bristles over their nostrils to keep wood chips out when they are chiseling tree bark.
- Powder Feathers – these are unusual in that they grow continuously and disintegrate at the tip. The barbs break down into a fine powder. Birds such as Herons (Ardeidae) use the powder to mop up the slime and dust that gets on their fronts during feeding therefore keeping their plumage clean. Powder feathers occur scattered throughout the plumage of most birds.
Flight control is an important factor of a bird’s aerial activity. A bird’s primary feathers at the wing tips can be fanned out and twisted to adjust their resistance to the air flow. This action provides the bird’s main form of aerial control allowing it to slow down, rise, descend and bank.
At slow speeds, the tail feathers are also important as they act as a rudder for manoeuvring and as a fanned out air brake for landing. Secondary flight feathers are less adjustable but form an arched aerofoil surface that generates lift as the bird moves through the air.
A small tuft of feathers on the anterior edge of the bird’s wing, called the alula or ‘bastard wing’, is a freely moving first digit, or the ‘bird’s thumb’, which is used for slow speed manoeuvring or landing. The alula is held flush againt the wing and controls the airflow over the leading edge of the wing by moving slightly upwards and forwards creating a small slot on the wing’s landing edge. This allows the wing to achieve a higher than normal angle of attack and lift without resulting in a stall.
The Colours of Feathers
There are many different coloured birds on our planet, some having the most beautifully coloured plumages one could imagine. The diversity of magnificent colours and patterns are exhibited by over 9,000 – 10,000 birds species throught the world.
Birds come in all colours of the rainbow with some reflecting certain colours of the light and others being the colour of the food they eat.
Feathers provide a bird’s unique colouration. Birds have excellent eyesight and can see more colours than humans as they can see into the ultraviolet range. Therefore, colour is very important to birds.
Feathers get their amazing colours in 2 ways:
Firstly, feathers are made from keratin in which coloured pigments are present. Pigments are colours found in animals and plant life. A bird’s colour is a combination of pigments and the placement of pigments on the bird’s wings and plumage.
Some birds have their pigments on their barbs while others have them on the shafts of their feathers. Birds produce three types of pigments that give feathers their different colours. The grey, black and brown pigment is called the ‘Melanin’. Melanins are usually Eumelanin – black to brown pigment produced by melanin and Phaeomelanin – yellow to red-brown pigment produced by melanocytes – melanin-producing cells located in the bottom layer (the stratum basale) of the skin’s epidermis.
Secondly, carotenoids, which produce the colours red, pink, yellow and orange, are acquired through eating plants or animals that eat plants. Another example of carotenoid colouring is Flamingos – they eat many shrimps which are pink, therefore giving the Flamingo its beautiful pink colouring.
Other pigments produce red and green feathers. Blue colouration found in many bird species including Bluebirds and Blue Jays are produced by nanostructures which under electron microscopes, look like sponges with air bubbles.
Birds can manufacture melanins in their own bodies, however, they can only acquire carotenoids through the food that they eat.
Another way colour is produced is the way that the light works with the feather structure. Some birds may appear dark and dull until the light is reflected on them. Brilliant colours are then on show as the feathers reflect the light creating iridescent colours of shining reds, greens and blues.
Protection and Conditioning
A bird’s outer feathers or contour feathers, gives the bird physical protection. Downy feathers beneath provide cushioning. Feathers also provide waterproofing which is important to water birds, seabirds, wildfowl and waders. As a bird preens, cleans to remove dirt and parasites and arranges its barbs, it also spreads oils from its oil glands over the feathers so that they resist water absorbtion and shed moisture easily.
Many birds moult twice yearly depending on species and replace their plumage with new feathers. Feathers do not last forever as they become worn and battered. The moulting process gets rid of damaged feathers and sometimes alters the birds appearance for a Spring breeding display or Autumn camouflage.
Brood patches are areas of a bare skin where feathers have fallen out during or prior to the incubation og eggs. Brood patches can be one large patch or several small patches depending on how many eggs are being incubated. For example, birds who incubate 3 eggs at a time, such as Gulls, have 3 brood patches whereas Ostriches who lay a large single egg would have one large brood patch.
These bare areas occur on the bird’s abdomen and are heavily fused with blood vessels which allows heat from the incubating bird to travel into the eggs and speed up the developement of the embryo. Brood patches are very important because the bird’s feathers are excellent insulators and therefore would prevent heat from transferring to the eggs.
Parasites On Feathers
The feather surface is home for ectoparasites also called feather lice (Phthiraptera) and feather mites. Feather lice typically live on a single host and can move only from parents to chicks or mating birds. Feather holes are chewing traces of lice on the wing and tail feathers. Birds maintain their feather condition by preening, dust bathing and bathing in water.
More Interesting Facts About Bird Feathers
- Some feathers, particularly in the more primitive birds, have a secondary smaller and less complicated shaft arising from the base of the calamus (the area the feather attaches to the bird), this is called an aftershaft.
- The outer ends of flight feathers in Owls lack barbules. This makes the edges softer and reduces the noise they make when flying. Silent flight helps an Owl catch its prey more easily.
- The feathers of primitive birds appear to grow at random all over the body, but in most orders the feathers appear in well defined patterns of rows or tracts called pterylae.
- The number of feathers a bird has depends very much on its size, its lifestyle and where it lives, generally, a third of a birds feathers are located on its head.
- A Ruby Hummingbird (Archilochus colubris) is a bird with the least number of feathers with only 940 feathers in total.
- The bird with the most feathers is the Whistling Swan (Cygnus columbianus) which can have as many as 25,000 during the winter.
- The longest and widest tail feathers of a wild bird belong to the Crested Argus Pheasant (Rheinhartia ocellata) which typically reach lengths of 173 centimetres (5.7 feet) and widths of 13 centimetres (5,1 inches).
- The longest feathers belong to the Onagadori (Gallus gallus domesticus), a domestic strain of Japanese red jungle fowl, whose tail can achieve lengths of up to 27 feet in length and who can take 3 or more years to moult.
- The longest tail coverts belong to the Indian and green peafowl at 160 centimetres (5.24 feet).
- The shortest tails and which are virtually non-existent are in Kiwis (New Zealand), Emus (Australia), Rheas (South America) and Cassowaries (Australia).
Feathers have many functions. Bird feathers help birds to fly and swim and are also for protection, insulation, waterproofing, camouflage and display.