A Bird's Flight
Very few things in nature delight us as the flight of birds. When it takes off into the sky, a bird fills us with wonder and becomes a symbol of freedom because it defies gravity which otherwise binds the rest of us, like a chain, to this earth.
There are many ways that birds fly. The height and speed, flapping (or not) of wings, angle of the body, trajectory of motion, even the silhouette against the sky – these factors, as well as others, vary from bird to bird. So much so, that the flight of each species is unique like a signature. After watching many flights, we can develop an intuition for this signature.
I'll give you an example. Last winter I was out in Purbachol, near a grove of bamboo and other trees, chasing some small birds, when for a split second, I saw part of a large brown wing in the sky through the canopy before it disappeared. Logic said that the wing belonged to a Brahminy kite, a very common bird with large brown wings. But my gut sensed something about the wing's motion that was unlike a kite's. I imagined the bird's trajectory and followed it, searching over the treetops. Eventually I spotted it perched on a tall bamboo. It turned out to be a rare oriental honey buzzard!
What is common among birds in flight is that their wings generate a force to counteract gravity. This upward force, called lift, must exceed gravity for the bird to become airborne. Obviously the heavier the bird is, the stronger the lift needed. In addition, a forward force, called a thrust, keeps the bird moving ahead.
Common small birds, such as sparrows or magpie robins (doels), fly fast in a straight line. However, the woodpecker's flight path is undulating. It goes up and down, like a wave. Birds which spend a lot of time on the ground, such as a coucal, are slow fliers as a rule. If threatened they take off clumsily and land in a spot close by.
On the other hand, the fastest living being on this planet is a peregrine falcon. From high up, it performs a move called a “stoop”, essentially diving straight down with its wings tucked in. Assisted by gravity, it reaches speeds exceeding 200 km/hour. Even at that speed, it makes fine adjustments in its trajectory, hitting the neck of its prey (usually another bird such as a pigeon) and breaking it instantaneously.
Closer to home, the drongo's (fingey's) flight is supremely acrobatic. When it hunts for insects close to the ground, it shows remarkable control over its movements, hovering and rapidly changing direction and speed. Kingfishers often fly fast and low, almost touching water, diving for fish. Smaller birds in the skies, such as swifts, will sometimes abruptly change direction and shoot straight up. Chances are, they are catching an insect in flight, but are too far for us to see that with the naked eye.
So the next time you see a bird in the sky, you might want to watch its flight carefully. Who knows, nature might reveal one of her secrets to you!
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