Fligh speeds of bird have been clocked many times, but usually at ground speed, and it is asserted that migrating birds travel faster when migrating than they travel at other times. The speed of most small migrating birds seldom exceeds 30 miles per hour. Most shorebirds average between 40 and 50 miles per hour, whereas many ducks travel 50 to 60 miles per hour.
At such speeds migrating birds may cover several hundreds of miles in a day or a night. It is routine for North American migrants to travel more than 500 miles nonstop across the Gulf of Mexico, where there are no midway islands. A turnstone, one of a cosmopolitan species of shorebird banded in Europe, covered 510 miles in 25 hours. Blue geese make the 1,700 miles from James Bay in Canada to coastal Louisiana in 60 hours.
Most routine migration probably takes place within 3,000 feet of the Earth, although David Lack, computing the altitude of British nigh migrants with radar, found that some small land birds often travel at 5,000 feet and may sometimes go as high as 14,000 feet. Radar has recorded birds at altitudes of 20,000 feet, perhaps not too surprising since many species cross both the Andes and the Himalayas during migration.
重點(diǎn)單詞：
clock : n. 時(shí)鐘,計(jì)時(shí)器,襪子上的花樣;vt. 繡花樣,記時(shí),記錄;vi. 記錄時(shí)間
assert : vt. 主張,聲明,斷言
migrate : vi. 移動,移往,隨季節(jié)而移居;vt. 使移居
exceed : vt. 超過,超越,勝過;vi. 超過其他
whereas : conj. 然而,反之,鑒于
routine : n. 常規(guī),日常工作,慣例,例行公事;a. 日常的,常規(guī)的
nonstop : a. 直達(dá)的,不著陸的,不休息的;ad. 不休息地;n. 直達(dá)車,直達(dá)行駛
turnstone : n. 鳥類的一種, 鶇
cosmopolitan : a. 世界性的
coastal : a. 海岸的,沿海的,沿岸的
compute : vt. vi. n. 計(jì)算,估計(jì)
altitude : n. 高度,海拔,高處
nigh : a. 在附近的;ad. 在附近地;prep. 近于
radar : n. 雷達(dá),電波探測器
surprising : a. 令人驚訝的
Andes : n. 安第斯山脈
Himalayas : 喜馬拉雅山脈
At such speeds migrating birds may cover several hundreds of miles in a day or a night. It is routine for North American migrants to travel more than 500 miles nonstop across the Gulf of Mexico, where there are no midway islands. A turnstone, one of a cosmopolitan species of shorebird banded in Europe, covered 510 miles in 25 hours. Blue geese make the 1,700 miles from James Bay in Canada to coastal Louisiana in 60 hours.
Most routine migration probably takes place within 3,000 feet of the Earth, although David Lack, computing the altitude of British nigh migrants with radar, found that some small land birds often travel at 5,000 feet and may sometimes go as high as 14,000 feet. Radar has recorded birds at altitudes of 20,000 feet, perhaps not too surprising since many species cross both the Andes and the Himalayas during migration.
重點(diǎn)單詞：
clock : n. 時(shí)鐘,計(jì)時(shí)器,襪子上的花樣;vt. 繡花樣,記時(shí),記錄;vi. 記錄時(shí)間
assert : vt. 主張,聲明,斷言
migrate : vi. 移動,移往,隨季節(jié)而移居;vt. 使移居
exceed : vt. 超過,超越,勝過;vi. 超過其他
whereas : conj. 然而,反之,鑒于
routine : n. 常規(guī),日常工作,慣例,例行公事;a. 日常的,常規(guī)的
nonstop : a. 直達(dá)的,不著陸的,不休息的;ad. 不休息地;n. 直達(dá)車,直達(dá)行駛
turnstone : n. 鳥類的一種, 鶇
cosmopolitan : a. 世界性的
coastal : a. 海岸的,沿海的,沿岸的
compute : vt. vi. n. 計(jì)算,估計(jì)
altitude : n. 高度,海拔,高處
nigh : a. 在附近的;ad. 在附近地;prep. 近于
radar : n. 雷達(dá),電波探測器
surprising : a. 令人驚訝的
Andes : n. 安第斯山脈
Himalayas : 喜馬拉雅山脈