Fascinating Feathers (Anatomy & Function)

by Lorraine Julien

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Feathers are a defining characteristic of birds. Simply put, if an animal has feathers, it is a bird. Although feathers play a major role in enabling birds to fly, creatures without feathers can also fly. Some examples are bats, which are fantastically agile fliers, and various types of insects. In fact, insects were probably flying millions of years before birds. Birds, however, have refined flying to an art form unmatched by any other present-day living organism.

Of course, feathers provide many other functions as outlined in a previous column: insulation, waterproofing, UV protection just to name a few.

Feathers are made up of keratin, a fibrous protein that is also the main structural element in hair, nails, reptilian scales, hooves, horns, etc.

Feathers consist of the following main parts:

• Calamus – hollow shaft of the feather that attaches to the bird’s skin

• Rachis – central shaft of the feather to which the vanes are attached

• Vane – flattened part of the feather that is attached on either side of the rachis (each feather has two vanes)

• Barbs – numerous branches off the rachis that form the vanes

• Barbules – tiny extensions from the barbs that are held together by barbules

• Barbicels – tiny hooks that interlock to hold the barbules together

You’ve probably noticed birds grooming themselves. When the feather arrangement is disrupted, the bird simply uses its beak to draw the barbs and barbules together again. In the case of some birds, such as waterfowl, grooming (or preening) also helps to draw waterproofing oil from the skin to the feathers.

Birds have a number of different types of feathers, each of which has a special function:

• Primary – long feathers located at the tip of the wing

• Secondary – shorter feathers located along the trailing edge of the inner wing

• Tail – feathers attached to the rump of the bird

• Contour – these are the insulating and waterproofing feathers that line the bird’s body

• Down – fluffy feathers located under the contour feathers to provide insulation

• Semiplume – located under the contour feathers that also provide insulation

• Bristle – stiff, long feathers around the bird’s mouth or eyes

Some feathers are unique to certain birds: Eagles and other soaring birds, for example, have long trailing feathers on their wings. These feathers are called “alulae” or “bastard wings” and provide extra lift.

Owls have the reputation of silent flight and it’s because the outer ends of their flight feathers lack barbules – meaning they are unzipped. This makes the edges of the wings softer – all the better for catching prey!

It’s interesting to note differences in the size of wings compared to bird weight and how flight is affected. This ratio of a bird’s wing area compared to its weight is called “wing loading”. An eagle, for instance, has a large wing area to weight ratio, meaning it has a lower wing loading, whereas a swallow has a small wing area to weight ratio and hence higher wing loading. As a result, the slow, soaring eagle is capable of much more energy-efficient flight than the fast, agile swallow. In my opinion, chickadees at the feeder are a good example of inefficiency: they fly to the feeder, take one sunflower seed, fly away, crack the seed open and eat it and then fly back. Seems not very efficient to me!

Another aspect affecting flight is the shape of the wings: the eagle has long, broad, rectangular wings for high altitude soaring whereas the swallow’s wings are broad at the base and then taper to a point enabling fast flight and sharp turns. Warblers have short, broad, round wings which enable it to hop from perch to perch and to also migrate long distances.

The colour of feathers is very important especially for attracting members of the opposite sex. Colour is derived in two ways: from the melanin that is manufactured in their own bodies and also from carotenoids in their food. Flamingoes are a good example of this – if they don’t get the right molecules in their food then their exotic pink colour fades away. This was discovered by zoos many years ago.

Feathers are very complex, as I’ve found out through research. In this quick overview, I hope you’ve found the subject as interesting as I have. My thanks to the www.earthlife.net website for much of the information contained here.

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Please feel free to report any observations to Lorraine Julien at naturewatching@gmail.com  or Steve Blight at natureobservations@rogers.com