Humans have always been fascinated with flight, and many of us are familiar with the cautionary tale of Icarus who, having donned wings made of wax and feathers, flew too close to the sun.
While there exist many species of animal able to glide through the air, only birds, bats, and insects have evolved the ability to stay airborne through the flapping of their wings. Of these three, it is the birds that top them all in their ability to fly at speed, with great endurance, over the longest distances, and while carrying the most weight; and so it is the birds that I will be discussing in this article.
Before we discuss flight, we must first understand the structures used by our feathered friends to take to the air – their wings! The bones in a bird’s wing are equviliant to the bones in your arms and fingers, only they have evolved over time to specialise in flight. Feathered wings are light, flexible, dynamic, and easy to fold away when they’re not being used. Wing bones are light and hollow, joined at the shoulder, and powered by large chest muscles. Whist in the air, the elaborate set of bones and tendons allow for fine-tune adjustments to be made to the angle of the wing, allowing for the most efficient flight possible. The wings normally control height and speed, while steering is directed with the tail.
Like a plane, birds must generate lift and thrust in order to fly. Lift rebels against the pull of Earth’s gravity, while thrust counteracts the forces of air-resistance and drag. Lift is generated by the flow of air over a bird’s feathered wings, while thrust is generated by the characteristic flapping that we are all familiar with.
Of course, there exists a great diversity of bird shapes and sizes even within our own State of Victoria, and so the mechanism of flight can differ among different species. Particularly there can be great differences in the methods of take-off and landing relative to a bird’s size. Small song-birds such as the white-plumed honeyeater can take flight in an instant, while larger-bodied birds like the Black Swan require more take-off time. Likewise, landing can be difficult for larger birds which is why swans often prefer to do so on the water, whereas song-birds can use their wings and tail to break in the air.
When it comes to speed the Peregrine Falcon wins the sprint competition with the ability to dive downwards in the air after prey at a dazzling 200kph. Meanwhile, at level flight, ducks and geese are among the fastest. Generally, birds rarely fly slower than 30kph in order to stay airborne.
Of course, while the flapping of wings is a familiar behaviour in birds, once in the air many birds choose the more efficient mode of staying airborne known as gliding or soaring. None do this quite like birds of prey like the Wedge-tailed Eagle or seabirds like the Australasian Gannet.
When the ground heats up from exposure to sunlight, the air above it also warms. This creates columns of warm air called thermals, which rise through the cooler (and therefore denser) air around them. Soaring birds use these thermals much like we use elevators – to effortlessly climb heights that would normally require a lot of time and energy! By spiralling around inside these columns of warm air, these birds can efficiently search for food, or travel great distances while on migration.
However, there are also other means of soaring. Cliffs and mountain ranges deflect wind in an upwards direction, creating updraughts which, unlike the temporary thermals, can blow for months at a time. If you’ve ever been to a windy cliff-face by the beach than this slope-soaring will be all too familiar – recall the gulls or sea-eagles that soared passed you in the breeze!
Flight is an amazing thing, and none perform it quite like the birds. So next time you step outside, spare a thought for any bird you might see flitting past, as they’re doing something pretty damn special.