Pliny the Elder [1st century CE] (Natural History, Book 8, 46): ...in Africa, which also produces a multitude of wild asses [asinorum silvestrium, onager]. In that species each male is lord of a separate herd of females. They are afraid of rivals in their affections, and consequently they keep a watch on their females when in foal, and geld their male offspring with a bite; to guard against this the females when in foal seek hiding-places and are anxious to give birth by stealth. Also they are fond of a great deal of sexual indulgence. - [Rackham translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 27.27): Among those which they call “grazers”, Africa has wild asses [Latin text: onagros]. Individual male asses rule over herds of females. The males stand in fear of lustful rivals. So it is that they watch over their pregnant females, and if opportunity arises, they bite off the testicles of the new-born colts. The females are thus wary and secrete their offspring in secluded places. - [Arwen Apps translation, 2011]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 1:39): The wild ass is called an onager... Africa possesses large untamed onagers wandering through the desert. Individual onagers lead herds of females. When male colts are born, the adult males become jealous and bite off their testicles, so that the wary mothers hide the male colts in concealed places. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Quadrupeds 4.80): Onager means wild ass. On the fifteenth day of the month of March, as Isidore says, it brays twelve times in the night, as many times in the day, whence it is known from this that it is the equinox. Africa has these great and untamed wanderers in the desert. Each one presides over herds of females. The fathers are jealous of male children, as Solinus says, and cut off their testicles, so careful mothers give birth in secret and hide the foal. The females of the onagers enjoy an abundance of lust, and not observing the mode of decency, often by this they become hateful to the males. Strange, since the female sex ought to be both more modest and more chaste, because it is contrary to nature, when a warm woman is colder than any cold man, as Ypocras says. As the Experimentator says, the onager, by natural energy, when pursued by dogs, emits its odorous dung to the dogs, by which it delays the dogs and escapes and runs away to safer places. Of all animals it hates the presence and habitation of men. it is intolerant of thirst. It cannot be tamed. It drinks the clearest water and no other. The male onagers who have no females, when the time of copulation has come, ascend to the summits of the mountains, and, in lustful desire, draw the wind with their noses, and bray so violently that the other animals are shaken with horror by their brays. In Poland the onagers are very large and ferocious. Their horns are very broad, but short and shaggy, they have horns on the head and long hairs under the chin. When these are pursued by the dogs, they draw in a great quantity of water with their noses, and boil it to such an extent that they pour it over the pursuing dogs as if on a boiling fire. - [Badke translation/paraphrase]

Guillaume le Clerc [ca. 1210 CE] (Bestiaire, Chapter 23): About the wild ass we shall tell / The truth—which we shall never gainsay— / As the book teaches us / Which does not fail nor err / In showing examples sensible / And true and pleasure-giving. / The book is not full of idle talk, / Examples it has most pleasing / With a wealth of mystery behind, / Which we put clearly in writing, / That one shall be able openly / To see the mystery laid bare. / In the desert of Africa the great / The man who goes seeking them / Finds these asses, of which I tell you, / There are none so big in all the world / And so they are not tamed. / In the deserts and the leafy woods, / In the valleys and the mountains, / Are herds of great numbers. / In each herd moreover / There is no more than one male / And he lords it over the females / Both in the plain and pastures. / The herd has but one stallion. / When the female has a foal, / If it is female, a female let it be, / But if the father perceives / That it is male, he loses no time / But cuts off its organs / With his teeth, for he does not wish— / I believe it is due to jealousy— / That with its members when full grown / It may be able to cover the herd. / When the month of March has come / And twenty and five days have passed, / Then the wild ass brays / Either in the plain or in the woods. / In the day it brays twelve times / And in the night twelve—know that— / Then do the country folk know well, / Who in the neighbourhood are settled, / That then are the night and the day / In a like state and of equal length. / Because it brays twelve times / From daybreak until evening / And twelve times likewise in the night, / They recognize without fail / That then is the equinox exactly / At that time and at that place. - [Druce translation]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.77): Onager is a wilde Asse, as Isid. sayth, and such Asses be greate and wilde in Affrica, and untamed, & goeth about in desart place: and each of them leadeth a company of females, & they have envy to the males when they be foaled, & bite off their gendering stones, & the females bée ware thereof, and hide theyr male foales in privy places. And Plini[us] sayth, li. 8. Betwéene wilde Asses and tame asses be gendered most swift Asses. And is a free beast at large, and not tamed, & lecherous: and hunteth oft mountaines and woodes, & though hée be of himselfe a beast that fighteth not nor gréeveth, yet by benefice of running and of lyghtnesse he overcommeth in desart both the Lyon and the Wolfe: and is a beast that maye well awaye with thirst, and suffereth it long, and abideth untill he maye drink that is covenable for him. And of him Phisiologus speaketh and saith, that in the 25. daye of March [the Spring equinox], this beast roareth twelve times in that day, and as oft in the night: and by his roaring the evennesse of the day and night is knowen among the Affrikes, and he saith, that alwaye he roareth as manye times in the daye, as there be houres in the day, and also in the night. And so woode men in mountaines of Affrica, in the which bée many wild Asses by the number of their roarings they account the diversitye of the day and of the night. This Beast is wise and wittie, and envious in smelling, and so when he is fervent in love, & wolteth not where his female is, hée goeth about and styeth uppon an high rocke, and openeth his nosethrilles, and draweth in ayre and winde, and knoweth and perceiveth by the wind and aire where his female is. And oft in mountaines hée fetcheth good hearbes and grasse, and hée loveth them well, and seeketh them with businesse in high mountaines, with travaile, and roareth for joy when he findeth therin gréene grasse and hearbes, but when hée knoweth that hée is hunted by men or by beasts, he flieth: and hateth greatly the company of men, and loveth well desart places and wildernesse. - [Batman]