Bird's nest made from the saliva of a certain species of swallow, known as Cave Swift. They are famous for building their saliva nests which are picked for human consumption and sold as an expensive delicacy in many, often Chinese shops (fig.). In Thailand they are known as rang nok and are collected from caves, such as Viking Cave on Phi Phi Leh Island (fig.), one of the Phi Phi Islands. The nests are composed of interlaced strands of saliva that dry up once attached to the cave wall and are made in the form of a shallow cup (fig.). The edible nests are used to produce the unique texture of bird's nest soup and are among the most expensive animal foodstuffs consumed by humans. In Chinese cuisine they have been traditionally used for over 400 years as they are rich in nutrients, such as high levels of calcium, potassium, iron and magnesium, known to provide certain health benefits. There annually three harvesting seasons for bird's nests. The first time around February-March. Afterwards there is a resting period  of one month to allow the birds to make their second nest. When ready they are harvested and another pause of three months is observed to allow the mother to lay her, to let them hatch and the chicks grow until they are strong enough to leave the nest and look for food on their own. Then the third nest is collected. There are white bird's nests and red ‘blood’ bird's nests. The saliva that the swifts regurgitate in order to build their initial nest in the first nesting season is pure white. They are good quality nests that we know by the name of ‘white bird's nests’ (fig.). The nests built later are called ‘red blood bird's nests’ (fig.), as it was earlier believed that in the making of a second and third nest the swifts had run out of saliva and were regurgitating their saliva until they started coughing up blood. But this is untrue. The red colour comes from rust in the caves. Due to the high humidity in these caves the rust infiltrates into the nest which absorbs it, especially nests build in the second and third nesting season are affected, as it is then the rainy season in Thailand, contrary to the first nest which is build during the cold season, around February-March. Thailand has three kinds of swallows that deliver bird's nest: the Edible-nest or White-nest Swiftlet, the German's Swiftlet and the Black-nest Swiftlet. The first  two species provide the white bird's nests, the latter gives us the black bird's nests, so called because its nest is mixed with dark feathers, but the nests of all three species are edible. The red ‘blood’ nests are more expensive, but also often faked by adding red pigment to white nests. In Bangkok's Chinatown a small bowl of white bird's nest soup costs around 200 baht, a large one around 300 baht. The downside of it all is the often illegal and indiscriminate collection of nests outside the harvesting season which endangers the swift population. Licensed as well as unlicensed harvesters, often inspired by greed, will collect or steal a nest as soon as it is large enough, whether or not eggs or chicks are inside. They get to them by climbing on high bamboo scaffoldings, a task not without any peril. In Chinese called yan wo. See also nok naang aen (fig.). 回