One of the most fascinating ancient uses of rhinoceros horn, with regard to later beliefs in the magical properties of the unicorn’s horn, was as an antidote to a poison commonly used in Bronze Age China. Innumerable written records dating back to the Spring and Autumn period state that this poison was made only in the South, where the rhinoceros lived. According to these documents, it was produced by pouring rice wine over the feathers of the zhen or “poisonfeather bird.” The question is, can we discover the identity of this extraordinary bird? First, let us examine some of the surviving textual evidence.
In the Classic of Mountains, which comprises the first five books of the Shanhai jing (The Classic of Mountains and Seas) and is tentatively dated to the third century B.C.E., there are several references to rhinos and poisonfeather birds. For example, in book five, chapter 8 of this famous mythogeographical work, the two are mentioned as together inhabiting a mountain called Lutedrum. Anne Birrell feels that such place names cannot be identified in reality, yet the ideas expressed in the book are key to a true understanding of early Chinese culture.
Two hundred leagues southeast is a mountain called Lutedrum. Its trees are mostly paper mulberry, oak, pepper, and dye mulberry. White jade stone is plentiful on the summit, and on the lower slopes are numerous lye-stones. The animals on this mountain are mostly pig and deer, and there are many white rhinoceros. Its birds are mostly poisonfeather birds. (Birrrell, 1999, 87)
Under the entry poisonfeather, bird, in her comprehensive index to the Chinese names and terms in the Shanhai jing, Birrell quotes Guo Pu (276-324 C.E.) who wrote the earliest commentary on the Classic. “Guo notes that this bird ‘is as large as an eagle; it is purple and green with a long neck and a scarlet beak. It eats snakes’ heads. The male is called ‘revolving sun’ and the female is called ‘Yin shade.’ He also notes this bird is so poisonous that if one of its feathers is put in someone’s drink or food, it will kill that person ” (Birrell, 1999, 248). Later texts confirm the peculiar attributes of this bird. Thus, in a famous Song Dynasty (960-1279 C.E.) book, the Pi Ya (Additions to the Erh Ya Dictionary), the description of the poisonfeather bird reads as follows:
If there is a zhen bird with poisoned feathers (because it eats poisonous snakes), and you dip them in wine, you will produce poison. The zhen bird looks like a goose but its colour is dark purple. Its beak is 7–8 cun (Chinese inch) long and copper-coloured. It eats snakes which dissolve in its mouth. If the droppings (excrement, dung) of the zhen bird touch stone, then the stone will dissolve. The feathers have poison. If they are mixed in wine then poison is produced. The only thing that can counteract this poison is rhinoceros horn [emphasis added]. Therefore in the place where the zhen bird lives, there are also rhinos.
Even allowing for a certain amount of Chinese hyperbole, a picture of this bird begins to emerge which can be used to identify it. It is native to South China, it looks like an eagle/goose, but is the size of an owl, it is purple/green/black with a copper/red beak, it eats poisonous snakes, and it has a sharp metallic cry. With this information in hand, together with a cursory woodblock print of a zhen bird perched on a branch (fig. 51) from the famous Ming dynasty encyclopaedia Sancai tuhui (Illustrated Encyclopaedia) by Wang Qi, I consulted my colleague Brad Millen in the Ornithology section of the Royal Ontario Museum.
Figure 51. The zhen bird on a branch. Woodblock print from the Sancai tuhui
Delighted by this challenge, he gradually narrowed down the possibilities, and after comparing their salient features with the Chinese texts, it became apparent that only one species truly fits the description of the zhen bird, and that is the crested serpent eagle (Spilornis cheela ricketti) (colour plate 22).
Plate 22. Adult crested serpent eagle (Spilornis cheela ricketti)
The crested serpent eagle is described by Brown and Amadon (1968) as an extremely variable species which inhabits tropical continental Asia from India east to south-east China, and the Malaysian and Indonesian regions south to Bali and east to the Philippines. Spilornis cheela ricketti is found in Vietnam, Yunnan Province, and south-east China north to Fujian Province. It has a large wing span of 455–490 mm, and is more sepia-brown in colour than other races. All species have a large fan-shaped crest, which gives them an owl-like appearance, but at rest, the crest is not usually noticeable (figure 52).
Figure 52. Immature crested serpent eagle on a branch
The breeding season of this eagle is marked by frequent soaring with noisy calling. It makes a variety of loud, clear, ringing and musical whistling or screaming calls in flight, but when not soaring it is an unobtrusive bird, difficult to locate and observe. It is often to be found in dense rain forest, hunting below the forest canopy. These birds frequent cultivation, villages, forest and woodland, but they are not a danger to game birds or poultry, and they are often tame and confiding, allowing close approach. Their normal method of killing is to drop almost vertically on prey after sitting immobile, sometimes for hours, on a perch. Their chief food is reptiles and vipers, tree snakes especially, and they will also pick up dead snakes as carrion. All prey is taken on the ground (Brown and Amadon, 1968, 360–64).
This description of the crested serpent eagle tallies well with the information about the zhen bird provided in the Chinese texts. Nevertheless, although the written sources of the knowledge of the use of rhinoceros horn as an antidote to poison are Chinese, this does not rule out the possibility that this information was also available elsewhere within the enormous geographic range of the crested serpent eagle. Yet until the liquid produced by soaking the feathers of this bird in fermented rice wine is chemically analysed, the kind of poison most commonly used in ancient China, and the effectiveness of rhinoceros horn as an antidote to this particular poison will remain a mystery. Perhaps someday, scientists living within the range of the created serpent eagle might take up this challenge and publish their results. In the Ornithology Section of the Royal Ontario Museum there are six splendid specimens of this bird. Unfortunately the chemicals used to preserve these specimens include arsenic, a fact which precludes them from use in such a scientific experiment.
The idea of using rhinoceros horn to detect the presence of poison, rather than simply as an antidote, is first mentioned in the writings of the Daoist adept Ge Hong (283-343 C.E.). In his most famous text, Baopuzi (The Master Who Embraces Simplicity) (Ware, 1966) in the chapter entitled Dengshe (Into Mountains: Over Streams) under the section “Method To Be Used in Order To Walk on Water or Stay Long Under Water” he writes as follows:
The (rhino) horn is made into a hairpin. When poisonous medicines of liquid form are stirred with the horn hairpin, a white foam will bubble up. After the foam has bubbled up, the harmful effect of the poison is gone. When non-poisonous substances are stirred with the horn hairpin, no foam will rise. In this manner the presence of poison can be ascertained.
Knowledge of these ancient Chinese uses of rhinoceros horn subsequently moved westward, supposedly first appearing in the writings of Ctesias whose book is dated to 398 B.C.E. Nevertheless, according to Richard Ettinghausen, there are compelling reasons to believe that this particular passage was inserted into the text at a much later date (Ettinghausen, 1950, 99 n.).
The dust filed from this (rhinoceros) horn is administered in a potion as a protection against deadly drugs…. Those who drink out of these horns, made into drinking vessels, are not subject, they say, to convulsions or to the holy disease (epilepsy). Indeed, they are immune even to poisons. (Ctesias, as quoted in Megged 1992, 6)
More than a thousand years after the lifetime of Ge Hong, the ancient Chinese uses of rhino horn as an antidote to the zhen bird’s poison, and as a means of testing for the presence of poison, would give rise to the central belief about the unicorn in Europe, that its horn (in this case the tooth of the narwhal which was called “alicorn”) could be used to detect poison. According to Shepard, “For two full centuries at least, roughly speaking from the final decades of the fourteenth century to those of the sixteenth, this belief was almost universal and unchallenged throughout Europe” (Shepard,  1982, 119). In China, on the other hand, chopsticks made of silver, which tarnished in the presence of poison, were used for this purpose.
A particularly intriguing reference to the rhinoceros and the zhen bird is found in another famous book of the Song Dynasty entitled Gewu Zhonglun (Summary Discussion of the Investigation of Things).
The rhinoceros and the zhen bird share the same watering places. If the rhinoceros does not bathe his horn in the water [dip his horn in to purify the water] before drinking, then the rhino will die [from drinking the poisoned water], because the zhen bird eats poisonous snakes, [and when it drinks] it poisons the water…. If you put the feathers of this kind of bird in wine and then drink it you will die.
This Song Dynasty belief in the power of rhino horn to purify water was also to become an important aspect of later unicorn myths in Europe, and formed the basis of the belief that the mythic unicorn, by dipping its horn into water, could purify it. Thus it is really not so remarkable, “that this trait—which I shall call, somewhat arbitrarily, the water-conning—exactly suited as it was to the uses of Christian allegory, was not reported in the Bestiaries of western Europe. To be sure it was known in the West, but not until late, and then chiefly in learned circles” (Shepard,  1982, 60, emphasis added).