作者：清风雅致 500)this.style.width=500;" onmousewheel="return bbimg(this)">screen.width-333)this.width=screen.width-333" border=0 dypop="按此在新窗口浏览图片"> Tom Kelly, of the National University of Ireland, has been studying bird strikes at Dublin airport. He has found that flying birds are actually quite good at avoiding aircraft--so good that the reason a few fail to do so owes more to miscalculation (or distraction by had weather of predators) than stupidity. The birds are, as it were, playing chicken with the planes, and sometimes they get it wrong. The first thing that Dr Kelly discovered is that birds do not seem to perceive aircraft as if they were other birds--and certainly not as if they were predatory birds. When faced with, say, a hawk, most birds will turn tail and fly away. When faced with an oncoming aircraft, they just bank out of its path. Experiments with caged birds, who were shown video clips of oncoming planes, have demonstrated that most start to react to an aircraft when the estimated time to collision is about five seconds. That may seem to be cutting things rather fine, but it is probably a reasonable compromise. Bird strikes, including those where only the bird dies, occur just once every few thousand take-offs and landings, so leaving things until the last few seconds works most of the time. From the point of view of a relatively short-lived animal that has a lot of other hazards to face, collisions with aircraft are not a major risk. However, from the point of view of man, a long-lived animal that faces few natural hazards, such collisions are unacceptable. Dr Kelly's suggested solution is that take-offs and landings might be preceded by the use of a laser beam to project an image that a bird would perceive as an expanding dot of light. (Readers who have been to concerts that feature laser light-shows will be familiar with this idea.) The dot would, Dr Kelly hopes, suggest a rapidly looming object and thus trigger the "banking" reaction before an aircraft came along. But then again, it might not. Or if it did, the birds might quickly learn the difference. 　 Comprehension Questions 1.Bird strikes occur most probably because______ A. birds are stupid B. birds are timid C. birds miscalculate D. birds are not afraid of predators any more 　 2.To birds an oncoming aircraft is_______ A. not predatory in nature B. more threatening than a hawk C. flying at too low an altitude (高度） D. too slow to pose any danger 　 3.Birds deal with aircraft by ______ A. flying aside B. flying headlong C. flying in the same direction D. flying onto the plane 　 4.Birds play chicken with planes because_____ A. they don't regard collision as a major risk B. they are extremely calculating C. they are no longer afraid of humans D. they regard planes as a major threat to them 　 5.The author implies that Dr. Kelly's suggested solution A. is costly B. is very revolutionary C. too complicated D. may be of limited use

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