雅思双语阅读——鸟类数量锐减 是天灾还是人为 雅思双语阅读
British birdwatchers are used to bad news. House sparrow numbers have fallen from an estimated 30m to 10m since 1966. Curlews have become a rare sight, their numbers plummeting by 50% in 15 years. Cuckoos, once-frequent visitors from Africa, have declined by 63% in the south-east in the past two decades. Earlier springs that confuse migratory birds, more efficient farming and the conversion of dilapidated buildings (good for nesting) into modern homes have all contributed to these woes.
But data released by the British Trust for Ornithology (BTO), a research charity, suggest some are soaring. Tracking bird populations by means of regular surveys, the figures give the clearest picture yet of 49 species acrossBritain.
Blackcaps, small woodland birds native to Germany and eastern Europe, are lingering after their summer sojourns: since 1967 numbers have increased by 177%. The little egret, a white heron-like bird, arrived from continental Europein 1989 and now numbers over 5,000. Wood pigeons, once found shyly cooing in forests, have boldly moved into cities and suburbs.
Environmental and agricultural changes have helped as well as disoriented birds. Modern farming techniques allow grain to be sown in the autumn rather than the spring; that helps wood pigeons feed in winter. Warmer winters mean rivers and ponds are less likely to freeze, providing the little egrets with food. James Pearce-Higgins of the BTO says that blackcaps benefit particularly from the increasing popularity of berry bushes (such as rowan and yew) in people’s gardens.
These species and others benefit from the British love of bird feeders. “I would be amazed if anyone feeds garden birds inEuropeas much as we do,” says Stephen Moss, a nature writer. First sold in 1964 by the Royal Society for the Protection of Birds (RSPB), a charity with over1mmembers, bird feeders took off in the 1990s when food such as sunflower hearts and nyjer seeds became widely available and the RSPB began to encourage people to feed birds throughout the year. (The bird tables found in other northern European countries, such as Finland and Germany, tend to be stocked only during the winter.) In 1987 only 17 species availed themselves of British feeders; these days 86 do.
Birders grouse nonetheless. Some of the species prospering, such as carrion crows and buzzards, are disliked. And migratory birds that extend their visits may provide competition for some avian natives. They are “muscling in and getting the first claim on breeding sites”, says Richard Cowser of the Sussex Ornithological Society. Like their human counterparts, residents of a small island buffeted by global winds, British birds will have to learn to compete.