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20 February 2009
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Small birds appear to move surprisingly quickly. Which species is really the fastest?
Peregrine In 1938 an American newspaper published a report from a pilot who was nose-diving at 170mph. The speed of his plane wasn't exceptional. What was remarkable was that he was passed by a diving peregrine stooping on some ducks "as though the plane was standing still". In 1955 another observer used a stop-watch to record the speed of needletail swifts crossing a valley in the Cahar Hills of Assam. The valley was two miles broad and the birds took between 32.8 and 41.8 seconds to traverse it. Thus the fastest speed was 219.5mph
Why are these claims difficult to accept? Chiefly because the speeds are so much in excess of the known speeds of such fast fliers as the racing pigeon. A careful experiment was conducted with Royal Air Force pigeons during the Second World War. The speed calculated was the average of a two-way flight. The fastest individual travelled at 58.7mph. Interestingly, this almost matches the quickest recorded speed for a European swift - a 'mere' 60mph. Furthermore, although they cannot fly, ostriches can trot at speeds of up to 45mph.
Naturally the pace of a bird running on land is much easier to measure accurately as its speed is due entirely to its own efforts, without help from gravity or wind. This is why contradictory figures are arrived at for birds in flight. A species diving in a strong tail-wind may well reach 100mph; climbing against the wind the same bird may clock only 10mph.
Brent geese Nearly all birds have two, and some three speeds: for cruising, emergencies, and migration. A bird that normally flies at 20mph may average 30mph on migration, and in panic flight before a predator may reach 40mph for a few seconds. Impressions can also be misleading. The smaller the bird the faster it seems to be travelling. Actually, larger birds like geese are among the swiftest, sometimes attaining an air-speed of a mile a minute. This is about twice the speed of small birds which appear to dart about so quickly.
The most impressive statistics are those charting the distances covered by birds in short periods of time. Lapwings are known to have crossed the Atlantic from Britain to Newfoundland in about 24 hours. They had to travel 2,200 miles and the average speed was, therefore, close to 90mph. But this does not mean that the lapwings flew at this speed. At the time a 55mph tail-wind was blowing across the Atlantic from Europe to Canada, accounting for over half the birds' speed. A paper bag, blown along by such a wind, would have travelled at over 60mph.
Seabirds probably hold the record for the fastest wind-assisted speeds. Albatrosses and shearwaters are long-winged and built like gliders. Several species spend their entire lives in the strong winds of the 'roaring forties' in the Southern Hemisphere. Ranging up to 350 miles in the course of a day's flying is part and parcel of their foraging routes over the ocean, but almost all of the effort is provided by wind. Indeed, the longest-winged species scarcely need to flap at all. Momentum is maintained by the strength of the wind over the sea and air turbulence created by waves gives the birds the lift they require. In complete contrast, hummingbirds are only able to hover by beating their winds constantly. They have the fastest wing-beat of all. The wings complete 75 up and down movements in a second. The house sparrow beats its wings almost 13 times a second in fast flight - the heron just two or three. Taking off requires most energy. If a bird is made to rise and fall several times in quick succession it will eventually stay panting on the ground.
ElderIn athletics and motorsport we tend to regard short sprints and fast acceleration as the measure of swiftness. How quickly can someone run 100 meters or how many seconds does it take for a formula one racing car to reach 60mph? Some of the quickest birds are shorebirds and wildfowl. Teal are the smallest duck and, unlike most wildfowl, do not need to taxi to take off. They spring into flight and twist and turn at speeds of up to 60mph. Golden plover are capable of outflying a pursuing peregrine in level flight. However, if the falcon can gain height and keep its quarry below it, then the added speed derived from gravity in a stoop will enable it to overhaul its prey. Should a peregrine attack from high above and drop like a stone on its victim, them its velocity rockets to a staggering 180mph.
Is there an official record-holder, a Linford Christie of birds? Like a true sports competitor, wind assistance should not be permitted to boost performance and the contender must be measured in level flight in still air. In practice this test has not been applied to birds - but it has in theory. The results are surprising. Engineers assessed body size, wingloading and general aerodynamic design and tested several bird models under laboratory conditions. Wildfowl again emerged as potential speed merchants. And the title of hot rod of the air? Because of its concorde-like front end and powerful, ergonomically-shaped wings and body, researchers concluded that, if it wanted to, the humble eider could be the fastest flying bird on the planet. Eiders, on the other hand, are more interested in using those turbo-changed wings to help them pursue food under water.
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