[al:新概念英语（四）] [ar:MP3 同步字幕版（英音）] [ti:Bird Flight] [by:更多学习内容，请到chazidian.com搜索“新概念”] [00:01.53]Lesson 23 [00:03.66]Bird flight [00:11.29]What are the two main types of bird flight described by the author? [00:17.83]No two sorts of birds practise quite the same sort of flight; [00:22.47]the varieties are infinite; but two classes may be roughly seen. [00:28.50]Any ship that crosses the Pacific [00:30.55]is accompanied for many days by the smaller albatross, [00:34.82]which may keep company with the vessel for an hour [00:37.76]without visible or more than occasional movement of wing. [00:42.57]The currents of air that the walls of the ship direct upwards, [00:46.67]as well as in the line of its course, [00:49.21]are enough to give the great bird with its immense wings [00:52.62]sufficient sustenance and progress. [00:55.93]The albatross is the king of the gliders, [00:59.41]the class of fliers which harness the air to their purpose, [01:03.44]but must yield to its opposition. [01:06.54]In the contrary school, the duck is supreme. [01:10.93]It comes nearer to the engines with which man has 'conquered' the air, as he boasts. [01:16.66]Duck, and like them the pigeons, are endowed with steel-like muscles, [01:22.40]that are a good part of the weight of the bird, [01:25.53]and these will ply the short wings with such irresistible power [01:30.00]that they can bore for long distances through an opposing gale [01:34.28]before exhaustion follows. [01:37.28]Their humbler followers, such as partridges, [01:40.62]have a like power of strong propulsion, but soon tire. [01:45.26]You may pick them up in utter exhaustion, [01:47.95]if wind over the sea has driven them to a long journey. [01:52.51]The swallow shares the virtues of both schools in highest measure. [01:56.72]It tires not, nor does it boast of its power; but belongs to the air [02:02.68]travelling it may be six thousand miles to and from its northern nesting home, [02:08.63]feeding its flown young as it flies, and slipping through a medium [02:13.50]that seems to help its passage even when the wind is adverse. [02:18.31]Such birds do us good, [02:20.45]though we no longer take omens from their flight on this side and that; [02:24.93]and even the most superstitious villagers [02:27.34]no longer take off their hats to the magpie and wish it good-morning.