Up and away

Birds move through the air with such grace that flying looks effortless to our eyes. But it takes tremendous effort to overcome the force of gravity and travel on nothing but air. For most birds, getting off the ground is the hardest part. Wings work best when air is blowing over them, so until a bird has built up speed it relies on muscle power alone. Once they get going, birds can conserve energy by catching the wind, gliding on air currents, or taking brief rests.

Flight patterns. Birds differ a great deal in their style of flight. Small birds tend to flap intermittently and close their wings for barely perceptible rests. As a result, their flight paths move up and down. Ducks and geese are non-stop flappers. They are fast and have enormous stamina, but they use up energy quickly. Long-winged birds like vultures and albatrosses are gliders. They conserve energy by riding on thermals or catching the wind.

Flocking together. Flying in a flock has several advantages. If each bird flies slightly to the side of the bird in front, it gets a lift from currents blowing off the leading bird’s wings. This is why ducks and geese fly in V-formations. Flocks also make finding food easier and give protection from predators. Starlings sometimes flock by the thousand, forming dark clouds that twist and pulse as the birds swoop past each other in prefect co-ordination.

Landing. Landing takes less effort than taking off, but it requires skill – especially in birds that land on a small perch. To lose speed, birds bring their wings into a more vertical position and lower their tails. Many birds have a special tuft of feathers (the alula) on the bend of the wing that helps stabilize airflow over the wings as they slow down, keeping them balanced.

Getting airborne. It takes tremendous effort for a swan to get into the air. Its wings, like the wings of an aircraft, only generate sufficient lift when a fast stream of air is flowing past them. So to overcome gravity, the swan must sprint with all its strength, using the surface of the water as a runway. Facing the wind helps, but in still air a heavy swan has to reach about 48kph to take off.

Partners and parasites. Sometimes it pays for a bird to form a special partnership with another species. By teaming up, they might be able to find food that neither could reach alone or defend themselves against a predator. Different bird species sometimes cooperate to drive away birds to prey; for instance small birds might “mob” an owl. In Africa, honey-guide birds team up with people to find and raid bees’ nests. When both partners benefit like this, the relationship is called symbiosis. Not all close partnerships work out so fairly, however. Often one partner takes advantage of the other: it becomes a parasite.

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