A clue to the source of the guano can be heard above the noise of the river.

鸟粪的源头能听到河水上空的鸟鸣。

 guano 英 ['gwɑːnəʊ]美 ['ɡwɑno]n. 海鸟粪；鱼肥料；鸟粪石 vt. 施海鸟肥料

The sound originates high up in the roof of the cave.

噪音因为山洞而被放大，

originate 英 [ə'rɪdʒɪneɪt; ɒ-] 美 [əˈrɪdʒəˌnet]vt. 引起；创作 vi. 发源；发生；起航

The entrance is full of swifts.

入口处聚满了雨燕。

swift英 [swɪft]美 [swɪft]n. 褐雨燕 adj. 快的；迅速的；敏捷的；立刻的 adv. 迅速地

They are very sociable birds, more than 200,000 of them share this cave in southern Guizhou province, the biggest swift colony in China.

 sociable英 ['səʊʃəb(ə)l]美 ['soʃəbl]adj. 社交的；好交际的；友善的，n. 联谊会

他们是社交性动物，约200000多的共享贵州南部的洞穴，中国最大的雨燕栖息地。

These days, Chinese house swifts mostly nest in the roofs of buildings,

如今 中国的家燕多数将巢穴建在建筑物的屋顶

but rock crevasses like these were their original home long before houses were invented.

但其实在房屋被发明出来之前，这样的岩缝才是他们原本安家的地方

crevasse英 [krɪ'væs]美 [krə'væs]n. 裂缝；破口，崩溃处

Though the swifts depend on the cave for shelter, they never stray further than the limits of daylight as their eyes can't see in dark.

 stray 英 [streɪ]vi. 流浪；迷路；偏离，adj. 迷路的；离群的；偶遇的，n. 走失的家畜；流浪者

尽管雨燕依靠洞穴遮蔽，他们却必定在日落前归巢，因为他们的眼睛无法在黑夜中看清事物

However, deep inside the cavern are the creatures are better equipped for subterranean life.

然而洞穴深处是一群更适应地下隐秘生活的居民

 cavern英 ['kæv(ə)n]美 ['kævɚn]n. 洞穴；凹处vt. 挖空；置…于洞穴中

subterranean英 [,sʌbtə'reɪnɪən] 美 [,sʌbtə'renɪən]adj. 地下的；秘密的；隐蔽的n. 地下工作者

A colony of bats is just waking up, using ultrasonic squeaks to orientate themselves in the darkness.

一群蝙蝠刚刚醒来，他们运用超声波在黑夜中确定自己的方位。

bat英 [bæt]美 [bæt]n. 蝙蝠；球棒；球拍；批处理文件的扩展vt. 用球棒击球；击球率达…vi. 轮到击球；用球棒击球

ultrasonic英 [ʌltrə'sɒnɪk] 美 [,ʌltrə'sɑnɪk]adj. [声] 超声的；超音速的n. 超声波

squeak英 [skwiːk]美 [skwik]vi. 告密；吱吱叫；侥幸成功n. 吱吱声；机会vt. 以短促尖声发出

orientate英 ['ɔːrɪənteɪt; 'ɒr-]美 ['orɪɛntet]v. 定向vt. 给...定位；使适应

Night is the time to go hunting.

夜晚是狩猎时间