Feather facts
Flight
Birds are one of the most successful vertebrates on earth. They number approximately 11000 species and many more subspecies, as opposed to approximately 6495 species of mammals. and 15000 species of fish.
In body shape the uniformity of birds is even more marked. The design of almost all species of birds is aimed at one main and vital activity only – flight. Their whole structure, build and shape solves the solutions to the problems imposed by the need for flight.
The structure of feathers
Feathers appear to have evolved from scales and are composed of beta-keratin, scales and feathers develop in a similar fashion, indeed birds have both and occasionally scales on a bird’s legs will develop feather tips.
Feathers are thought to be stronger than any wing structure made by man and yet at the same time incredibly flexible so that on the down stroke of flight they can bend on occasion, almost at a right angle to allow both lift and forward movement.
The amazing, streamlined shape makes birds the fastest living creature on our planet, in the air at normal flying height the large falcons can reach speeds of up to 150mph and an Arctic penguin has been timed at an estimated 22 mph under water.
Feathers are made up of a shaft, called the rachis and the vanes on either side, which in turn are made up of barbs that are arranged side by side up the shaft of the feather. Barbules grow from the barbs, these which have tiny hooks that interlock in a similar way to velcro, to give the vane its shape. The short bare part at the base of the shaft is called the calamus, if you cut in crossways, it is basically hollow and very light. There is an opening at the very tip of the base, this where the blood supply enters the feather while it grows. Once a feather is fully grown, the supply of blood is sealed off and the feather itself becomes ‘dead’, similar to the ends of our nails. On most of the flight feathers the vanes are of unequal length, this gives the feathers the ability to twist under air pressure. The much larger flight feathers are attached to bone by connective tissue, and have little or no down at the base. All the other feathers are attached to muscles below the skin.
Feathers - their uses
Feathers are the most distinctive characteristic of a bird. They are perfectly adapted for:
flight
thermoregulation (keeping warm and cool)
protection for the body
defence both physical and visual
incubation of eggs
brooding of young
display both visual and audio
camouflage
hunting by touch
Even in some cases, to carry water
Basic wing shapes
There are four basic wing shapes and most birds will fit into one of these categories. There are of course exceptions, particularly the non flighted birds, such as Penguins, or Ostriches.
The basic shapes are as follows
The broad, soaring wings – slotted wings of the buzzards, vultures, crows and storks are designed for soaring and gliding, taking advantage of any updrafts of warm air that occur over land and allow the birds to fly using almost no energy.
The elliptical or short rounded wing of forest living birds and ground living birds, such as the pheasants, doves, woodpeckers, perching birds (passerines) and the true hawks or accipiters, Sparrowhawks and goshawks. This wing shape gives fast take off speeds, sprinting ability and great manoeuvrability in confined spaces such as forests.
The long very narrow wings – high-aspect-ratio wing of the soaring sea birds such as gulls and albatrosses are designed for high-speed gliding in the strong winds of the earth oceans, often very close to the water taking advantage of the spurts of updrafts from the waves.
The long pointed wings without slots – the high speed wing – are found on birds that feed or hunt in the air or rely on high speed, such as the swifts and swallows and the falcons, these wings give high speed and fast level flight, but is not so good for manoeuvrability or stopping quickly.
Types of feather
There are seven types of feathers
The contour feathers – those smaller feathers on the body and wings and tail that give the bird its shape.
The flight feathers – the large wing feathers called the primaries and secondaries also called the remiges –and the large tail feathers, also called retrices . But don’t be mislead – not all tail feathers are what they seem. For example the huge and very beautiful tail feathers of the peacock or the cockerel are not its flight tail feathers, they are the contour or covert feathers that have grown out of proportion to the bird, often only for display and sometimes lost after the breeding season. So they have to be feathers that the bird can do without.
The semi plume is a feather with a shaft, but the vane of the feather is very soft, for shape and warmth. They are really intermediate feathers coming between the contour feathers and the down
Then there are the down feathers which are the incredibly soft under down on a bird which give it the insulation for warmth. They have virtually no shaft (or rachis) and very few barbules – the little hooks that hold the vanes together in a consistent shaped surface – instead the barbs are soft and airy and hold warmth superbly. Some species of birds – such as the herons have what are called powder downs – the down breaks up into a fine powder which the birds then preen onto their outer feathers as a water repellent. These powder downs grow continuously to replace themselves. The soft almost cotton wool like appearance of the down feathers and the semi plumes are called plumaceous vanes.
The final three are the bristle – which is what the name suggests – a bristle, seen around the beak of owls, and other nocturnal birds such as the night jar. These are used as sensitive tools and on occasion a funnel so that if touched the bird automatically snaps up food – such as flying insects which are directed at its beak
The eyelash is similar to the human eyelash with some added tiny down at the end
Lastly the filoplumes which are bristles with a tiny plume of feather vane at the tip, these very odd feathers are always found next to contour feathers and unlike all the other feathers have no muscle at their base, but many nerve endings, so they act as sensory organs, registering pressure and vibration and assist in keeping the feathers in place and adjusting them for flight, insulation and bathing.
Number of feathers
One would imagine that the feathers on a bird are evenly distributed, but in fact they grow from quite distinct tracts, or lines (called Pterylae), with quite large bare areas of skin (apteria), these may get covered with down or semi plumes for warmth. The size of the bare areas apteria vary, water birds have smaller bare areas and penguins have almost none. The main function of the apteria is for cooling the bird when they are exposed.
Most birds have 10 primaries, but these can vary from 9 to 12. Humming birds have the least number of secondaries 6, Albatrosses have as many as 32 and a Bateleur Eagle has 35. Tail feathers vary from 6 (some song birds) to 32 (Bulwer’s Pheasant,) but more commonly birds have 10 or 12.
The total number of feathers on a bird varies from species, size, sex, age, health, season and temperature of habitat.
Songbirds have between 1500 – 3000 – 6% – 7% of their body mass. The lowest recorded number is 940 for a humming bird and the highest is 25216 for a swan, 40% of which were on the head and neck. But for all their incredible lightness and strength, they take up a goodly part of a bird’s total weight. One Bald Eagle weighing 4082gs had feathers that weighed 677g (17%) when its dried skeleton weighed only 272g (7%). Most birds have more feathers in winter than in summer, similar in fact to mammals growing a winter coat for warmth.
Feather colour
The huge variation in the plumage colour in birds is produced by a combination of very few pigments, of two main types. The melanins are responsible for blacks and yellows, the carotenoids which also produce yellows as well as the reds. The melanins are made by the bird’s body, but the carotenoids are obtained in the diet. This is beautifully shown in flamingos who, if not fed the correct diet will lose their pink colouration and turn white.
The colours on a bird can be classified either as iridescent or non-iridescent. The glorious colours of hummingbirds, or kingfishers and surprisingly the less obvious iridescence of the Turkey vultures are really only seen at their best at certain angles, when light touches the surface. The colours on non-iridescent feathers can be seen from any angle.
A feather may have different pigments and structures on different areas, so the overall colour may be a combination of both. For example in the Green Magpie the green is the result of a yellow Pigment overlying a blue structural colour. Because yellow fades in the sun, the magpies who live in open areas are much bluer than those living in shaded forest areas.
Some birds will change their colour prior to the breeding season. Some do it by parts of the feather wearing away leaving a different colour for the breeding season, the darker pigments are much stronger and more resistant to wear and abrasion.
Others achieve a partial moult, which means they use less energy than growing all their feathers, and instead just moult and re-grow the display feathers which tend not to be flight feathers.
In many species the male is far more colourful than the female, for example, the American Kestrel, it is thought that this is because the colour assists the male in attracting a female and the female is drabber as this assists her camouflage whilst she is incubating eggs. However there are a number of other possible theories as well, often the females do the bulk of the incubation and initial care of the young, so being well hidden is very important. It would probably be fair to say that we can guess at the reasons, but don’t really know for sure.
Colour of course is vital for camouflage. The wonderful soft colours of the owls and nightjars, mean they can sit quietly against the bark of a tree and literally disappear, similarly the Woodcock fades to nothing in the undergrowth. It is thought that the areas of white feathers on the fishing eagles may disguise and break up their silhouette when they hunt for fish low over the water.
Some upland birds such as ptarmigan have a white winter plumage to help them hide in the snows of winter, they even have a speckled plumage as they change from brown to white, which has the same effect of camouflage in the autumn. Male Snowy Owls are almost pure white in adult plumage, but the females who do the bulk of the incubation of the eggs, on the ground in the Arctic tundra – after most of the snow has gone, are much more heavily marked with black – which again camouflages them whilst they are sitting on the eggs.
The colour changes in birds can be for a number of reasons, many birds have juvenile and adult plumage, some who take several years to gain their adult plumage have a sub adult phase too. Bald Eagles are a prime example of this, with the dark juvenile plumage, the more mottled and streaked plumage of the sub-adults and the eventual white head and tail of the adult birds.
Special characteristics
Even more interesting is the fact that feathers have different scents, they have a clean musky smell that can be different in different species and particularly in young growing birds.
A brand-new, fully-grown feather has a bloom on it like the bloom on the skin of a grape or a plum, and like the fruit, once touched, that bloom can be marked and spoilt.
The wider side of the vein on the large vultures such as Griffon Vultures and Condors looks almost pleated when the feather is at rest, but once in flight those pleats flatten out to allow the vane to expand with the tremendous curve put on the feather by the air pressure, without splitting apart the zipped up barbules, it’s a very clever design
It has been noted that the white feathers on King Vultures and Bald Eagles actually turn white over time, rather than growing in white after the old feather is moulted.
Care of feathers - moulting
Most birds have an annual moult, which normally occurs during or following the breeding season, and can take from four to sixteen weeks to complete. The larger the bird, the longer the moult and with some species, such as the eagles and large vultures, a complete moult can take two to three years. Some birds, such as certain of the waders that partake in long migrations will hold up their moult during the migration period and then continue it once they have reached their wintering grounds, thus saving valuable energy.
Eleonora’s Falcons moult in their wintering grounds, probably because they breed very late in the summer. Others like some of the ducks moult all their flight feathers in one go and re grow them all at once, it is called going into Eclipse – but then they have the element of water as well as land to aid them in feeding, hiding and defence. Some species change some of their feathers twice a year, they will go into winter plumage for camouflage in the snow and a darker summer plumage for camouflage when the snow is gone.
Care of feathers - preening
To keep feathers clean and ready for flight, birds preen, with enormous concentration and time spent oiling and cleaning them, zipping them up and on general maintenance of what is their most vital tool. They use their beaks, and many will bath to assist with cleanliness, vultures for example will fly up to 20 miles to find water to bath after feeding.
Feathers and humans...
For thousands of years humans have admired birds and their feathers, although not always to the benefit of the birds. The Bald Eagles and Golden Eagles in North America were killed in their thousands to provide the well recognised Native American headdresses, Birds of Paradise are utilised in the same way by tribes in South America. In the early part of the last century, it was the destruction of birds to provide feathers for fashionable ladies hats in the western world that started the movement in the UK and the US to give birds legal protection. Now thank goodness, for the most part, we are able to admire and be amazed by birds and their feathers through film, photography, and the chance to see birds up close as living breathing and vital parts of our environment. Feathers are without doubt one of natures wonders, a world without birds and consequently feathers is not even to be contemplated.
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