It’s called that because the bird barfs up “long strands of sticky saliva onto the wall of a cave or house” to build its nest. The barf-spit hardens into strands that stick to the wall of a house or cave or tree or whatever.
Many traditional Chinese folks think that if you then take that barf-nest and soften it in broth to make a soup, you’ll be super-healthy. There is no actual evidence to support this, but you know how people are. And guess what: the bird nests can sell for $1,000 a pound!
So in Indonesia, people are building human-size bird houses. That is, they build actual houses and they’re hoping that edible-nest swiftlets build barf-nests there. So who’s crazier? The people who build actual houses for birds, or the ones who eat barfy-bird-homes?