The lightness of being ... birds

An observation

September 09, 2001

I have been learning about birds. ... The way they fly is extremely complicated and instructive, as any aircraft designer can tell you. Like jets, they create vacuums with their wings and they use high air currents to achieve immense speeds in relation to the land. I remember standing on a 3,000-feet-plus peak in the remote Highlands and watching a flight of grey-lag geese high above, their wings beating slowly and steadily. That great ornithologist John Lister-Kaye, who was with me, calculated that their groundspeed was over 60 miles an hour. They were riding a wind speed of perhaps 50 mph. For though average wind velocity at ground level is 10 mph or less, it rises to 65 mph at 10,000 feet. At 30,000 feet, the height of Everest, it is about 100 mph. And four kinds of bird - choughs, curlews, godwits, and lamergeiers - have been seen near the top of Everest. It's not surprising that one Indian bird, the spine-tailed swift, has been clocked at 200 mph. Usual groundspeeds, however, are between 20 and 40 mph for most birds.- Excerpted from an article by Paul Johnson in The Spectator (London)

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