Since swiftlets spend their lives airborne, they make their nests hundreds of feet above ground in cliffsides. Some swiftlets have sonar to guide them, like bats, and can fly several miles into dark caves to produce the next generation.
雨燕終生以廣闊天際為家，為利於飛行，就在離地面上幾百公尺的岩壁上築巢，有些雨燕擁有類似蝙蝠、以聲音引導方向的本領，可以深入好幾英哩的黑暗洞穴中，繁衍後代。