托福阅读机经：不会飞行的鸟类

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托福阅读机经：不会飞行的鸟类

摘要：托福阅读机经：不会飞行的鸟类.以前，存在没有翅膀的鸟。因为它们生活在岛屿上，没有天敌。这种鸟翅膀肌肉不发达是因为发展翅肌的能量还不如自己保存体力。

又说到后来它们因为环境等因素不得不进化，而没有进化的鸟就因为人类入侵而灭绝了。

不会飞的鸟是指已失去飞行能力的鸟类，取而代之的是奔跑及游泳的能力。虽然如此，但普遍相信它们都是由懂得飞行的共同祖先进化而来。现存约有40种不会飞的鸟类，包括企鹅、鸵鸟及鹬鸵(奇异鸟)等广为人知的物种，及部分属于其他目的物种。除了诸如鸵鸟等大型的不会飞的鸟仍拥有强而有力的爪去对抗猎食者之外，大部分不会飞的鸟所面对的均为没有太多捕猎者的环境、或是隔绝性的海岛，花费极大气力的飞行并不符合效益，因此它们的进化倾向失去这种能力。

相比起其他地区，新西兰有较多的不会飞的鸟类，如奇异鸟、企鹅及南秧鸡等。其中一个原因是在人类首次踏足这个土地上时(约1000年前)，岛上并没有地栖形的捕猎者，它们最大的敌人反而是大型的猛禽——飞行并不是逃避敌人的有效方法。

不会飞的鸟类在面对人类所造成的威胁时冲击较大，因此它们面临灭绝的机会也较高;幸运的是它们也较易被圈养保护，简单的栏杆已是有效的工具。人类很早就懂得牧养鸵鸟以取得其羽毛，现在的规模更大，以取得其肉作食及皮作为皮革制品。

【英文题源】

Flightless birds are birds which lack the ability to fly, relying instead on their ability to run or swim. They are thought to haveevolved from flying ancestors. There are about forty species in existence today, the best known being the ostrich, emu, cassowary, rhea, kiwi, and penguin. It is believed by somecitation needed that most flightless birds evolved in the absence of predators on islands, and lost the power of flight because they had few enemies — although this is likely not the case for the ratites (the ostrich, emu and cassowary), as all have claws on their feet to use as a weapon against predators.

Two key differences between flying and flightless birds are the smaller wing bones of flightless birdsand the absent (or greatly reduced) keel on their breastbone. The keel anchors muscles needed for wing movement. Flightless birds also have more feathers than flying birds.There are at least another two possibilities as to why flightless birds such as ostriches and emus have wings, either.

The wings are indeed “useless” and derivedfrom birds that once could fly. This is possible in the creationist model. Loss of features is relatively easy by natural processes, whereas acquisition of new characters, requiring specific new DNA information, is impossible. Loss of wings most probably occurred in a beetle species that colonized a windy island. Again, this is a loss of genetic information, so it is not evidence for microbe-to-man evolution, which requires masses of new genetic information.Some possible functions, depending on the species of flightless bird, are: balance while running, cooling in hot weather, warmth in cold weather, protection of the ribcage during falls, mating rituals, scaring predators (emus will run at perceived enemies of their chicks, mouth open and wings flapping), sheltering of chicks, etc. If the wings are useless, why are the muscles functional, allowing these birds to move their wings?

New Zealand has more species of flightless birds than any other country. One reason is that until the arrival of humans roughly a thousand years ago, there were no large land predators in New Zealand; the main predators of flightless birds were larger birds.The flightless birds of New Zealand are a principal feature of the 'edge ecology' of the country.In an island environment isolated fromthe rest of the world for more than 80 million years, and free of mammal predators, a number of birds developed flightlessness andeccentric habits. Each of them filled different ecological functions; moa and kakapo as forest browsers, takahe as grass eaters, and kiwi and wrens as ground insect eaters - roles taken by mammals in other ecosystems. Many of the birds are unafraid of humans, a common characteristic resulting from the absence of predators, which became deadly when human hunters arrived. The takahe, for example, is the largest living member of the rail family which is found throughout the Southern Oceanic islands.They were hunted until they were rarely found in the 19th century. None were seen after 1900 and it was declaredextinct, but amazingly, 200 pairs were found in a remote region of Fiordland in 1948. The North Island takahe is extinct, but about 220 of the South Island species continue their dramatic brink of extinction existence.

Some flightless varieties of island birds are closely related to flying varieties, implying flight is a significant biological cost.The smallest flightless bird is the Inaccessible Island Rail (length 12.5 cm, weight 34.7 g). The largest (both heaviest and tallest) flightless bird, which is also the largest living bird, is the Ostrich (2.7 m, 156 kg), although some extinct species grew to larger sizes.

Flightless birds are the easiest to take care of in captivity because they do not have to be caged. Ostriches were once farmed for their decorative feathers. Today they are raised for meat and for their skins, which are used to make leather.There were also other families of flightless birds, such as the now extinct Phorusrhacidae, that evolved to be very powerful terrestrial predators.

【托福高频词】

evolved

citation

from

derived

roughly

predators

eccentric

dramatic

extinct

terrestrial

【长难句分析】