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They're cave swiftlets.
它們就是洞金絲燕
Like bats, they use echolocation to navigate.
和蝙蝠一樣，它們也利用回聲定位來導(dǎo)航
We need lights to see what's going on,
我們必須有光才能看清前方的路
but in the pitch black, the swiftlets manage unerringly to locate their individual nesting sites,
但是金絲燕卻能在黑暗中準(zhǔn)確無誤地到達自己的筑巢點
which are only a few centimetres across.
而它們的巢窩相隔不過幾厘米遠
It's a remarkable skill and one we still do not fully understand.
我們至今仍未能完全了解這種了不起的本領(lǐng)
These birds are unusual for another reason.
這些鳥之所以特別還有另外一個原因
Their little cup-like nests are made entirely from threads of saliva.
它們小巧的杯狀燕窩完全由唾液絲筑建
It takes more than 30 days to complete one.
每個燕窩得花上30多天才能完工
Their nests are very precious objects, and not only for the birds.
燕窩是非常珍貴的東西，不僅只是針對這些鳥而言
For 500 years, people have been harvesting the nests of cave swiftlets. It's a very risky business.
500年來，人們一直采集洞金絲燕的燕窩。這是一項非常危險的工作。
With virtually no safety equipment and using ladders made from forest vines,
事實上沒有任何安全措施，采集者利用樹藤編成的梯子
the gatherers climb into the highest reaches of the cave, often more than 60 metres from the floor.
爬到洞穴的最高處，通常高出地面60多米。
The work may be hazardous in the extreme, but the rewards are great.
這項工作看起來極度危險，但卻能得到豐厚的回報。
