Sunday, June 14, 2009

The fastest, the slowest, the highest birds

In the same way that human speed and endurance records are constantly being broken, so too the animal world's fastest, slowest and highest continues to change as naturalists discover previously unknown facts. For instance, it was widely accepted among naturalists that the white-throated spinetail swift of northeast Asia and Japan was the world's fastest bird, reaching speeds of up to 150 km/h (95 mph). But researchers have fitted speedometers to the legs of the peregrine falcon and discovered that when hunting its main prey of ducks, pigeons and other birds, it makes a 'stoop' or power dive at 160 km/h (100 mph). Sometimes this falcon knocks the head clean off its victim as it strikes it in midair with its strong talons.
Peregrine Falcon (Falco Peregrinus)

By contrast, the slowest flying (rather than hovering) bird is the American woodcock. The male's display fight has been measured at only 8 km/h (5 mph). It circles high above its woodland territory at dusk, giving twittering calls before zigzagging down to Earth on whistling wings. The combination of the slow, circling flight and the sudden descent seem to impress the females waiting on the ground.

Although birds such as kestrels and buzzards can remain stationary in midair by flying into the wind, very few birds can truly hover. Only the hummingbirds have mastered the art. They have the fastest wing beats of any bird - up to 78 beats per second - and can fly backwards as well as hover. Their short 'arm' bones, stiff wing joints and flexible shoulder joints allow them to rotate their wings in a figure of eight, and thus achieve their feats.

Other birds flap their wings very slowly - some large vultures do so only once per second. Albatrosses, using wind current to their best advantage, are able to soar over the waves for days on end with scarcely a flap of their great wings, which, with a span of up to almost 4 m (12 ft), are the longest of any living bird.

Soaring to new heights

Some animals fly fast, others fly high. The great majority of birds remain below 150 m (500 ft) for much of their lives, perhaps reaching 1500 m (5000 ft) when migrating. But bar-headed geese have been seen by mountaineers flying over the Himalayas at a height of almost 9000 m (30 000 ft). The undisputed holder of the bird altitude record is the Ruppell's griffon vulture that collided with an aircraft at 11 250 m (36 900 ft) over western Africa in 1973.
Ruppell's Griffon Vulture (Gyps rueppellii)

Birds can survive in the thin atmosphere of such heights, where humans would need oxygen masks, because their circulatory system is far more efficient at extracting oxygen than our own. The high-fliers can also cope with very low temperatures: whooper swans, for instance, have been recorded at heights where the temperature was as low as -48 degree C (-54 degree F).

1 comment:

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