Hon Yen is most famous for Yen Sao which is the name of the nest of Salangane or swifts. The locals harvest the bird nests (considered a delicacy) used in soups. These nests are processed and exported to Taiwan and Hong Kong.
The birds build their nest high on the walls of the cave on the islands. To access the nests, harvesters must climb on ladders fashioned from bamboo. Because the caves must remain dark lest the birds are scared off, many climbers fall to their death every year trying to harvest the nests.
The bird nest comes in two types, white and red nests. The nest are fashioned by the Salangane that make their homes in caves. The nest are made out of the birds saliva. Usually, a typical bird creates one nest a year during springtime using both parents saliva. Because there is such a demand for their nest (thought to have medicinal qualities), the locals began to remove the nest several times a year causing the birds to have to continue producing the nests.
The red variety of nests are a result of the birds having to create so much saliva for the new nests that they cough up blood along with their saliva causing the nest to take on the red color of their blood. This variety of nest costs their weight in gold or more in the retail market of Hong Kong or Taiwan.