Pliny the Elder [1st century CE] (Natural History, Book 10, 35; 10, 42): [Book 10, 35 ] Blackbirds ... also migrate in a similar way to neighboring districts; but these do not moult their plumage, and do not go into hiding, being often seen in the places where they forage for winter food. [Book 10, 42 ] There is another remarkable fact about songbirds; they usually change their color and note with the season, and suddenly become different... The blackbird changes from black to red; and it sings in the summer, and chirps in winter, but at midsummer is silent; also the beak of yearling blackbirds, at all events the males, is turned to ivory color. - [Rackham translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 7.12): There is something worth relating about the birds in this same place [Arcadia]. Although in other places, blackbirds are dusky, around Cyllene they are a very bright white. - [Arwen Apps translation, 2011]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 7:69): The blackbird (merula) was called medula in ancient times, because it makes music (modulare). Some say it is named because it flies alone (mera voluns). All are black, except in Achaea where they are white.

Hugh of Fouilloy [ca. 1100-1172 CE] (De avibus, chapter 48): Isidore says of the blackbird, "The blackbird (merula) in ancient times was called 'measure' (medula), because it sings. Others say it is called [blackbird] because it flies alone, as though in unmixed (mera) flight. Although this bird is black in all [regions], it is nevertheless white in Achaia. The blackbird is a small but black bird. [It signifies, moreover, those whom the blackness of sin stains. By its own sweetness of voice the blackbird stirs the mind to a state of delight]. Furthermore, it indicates allegorically those whom carnal desire tempts by suggestion. Indeed, concerning that [desire] the blessed Gregory wrote in the Book of Dialogues, "Just as [a blackbird] in flight presented itself to the blessed Benedict, so the great man, after the departure of the bird, was tempted by wanton desire." For as [Gregory] said, "But one day while the blessed Benedict was alone, the Tempter appeared. Now a dark and small bird, called popularly a blackbird, began to fly about his head and to hover violently in his face, so that it could have been caught by hand if the holy man had wanted it checked. But at the sign of the Cross the bird departed. Yet following the departure of this bird there occurred such a temptation of the flesh [as] the holy man had never before experienced." For indeed he saw at length a certain woman whom the Evil Spirit brought before his mind's eye. And with such passion did [the Devil] inflame the spirit of the servant of God for her beauty that the flame of love could scarcely be contained in his breast, so that he almost decided to desert the monastery, vanquished by pleasure. When suddenly, by heavenly grace, his gaze is turned the other way, and seeing thick bushes of nettles and thorns growing nearby, having stripped off the garment with which he was covered, he threw himself naked on the pricks of the thorns and burnings of the nettles. And having rolled about there for a long time, he departed, his whole body wounded by [the thorns and nettles], and cast out from his body the wound of the mind through the wounds in his flesh, because he exchanged pleasure for pain. So the blackbird in flight is enticement, tempting with pleasure. Therefore, whatever people wish to cast out the sensual pleasure of the blackbird must be turned to the improvement of discipline by the example of the blessed Benedict, and thus through bodily pain draw out the distraction of the mind. As Isidore declares, there are white blackbirds in the Achaian regions. The white blackbird is [allegorically] a virtuous inclination, but Achaia defines the laboring sister. There are two sisters, Rachel and Leah, that is to say, the active life and contemplative life. Leah defines the worker. The active life teaches us to show mercy, to instruct the immature, to have the cleanliness of chastity, to work with one's own hands. This is the work of the active life. This is the laboring sister. This is Achaia, that is to say, the active life. Therefore, they who live chastely in the active life are like white blackbirds in Achaia. - [Clark translation, 1992]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Birds 5.88) The blackbird (merula), as Jacobus says, was formerly called medula, because its voice is modulated [moduletur]. It has a wonderful tone of voice, especially when it looks forward to the coming of spring; for in winter the blackbird is silent. There was a blackbird, who, trained in human art, sang nine notes in order according to the music so perfectly, that none of the musicians could imitate it in any degree. This was at that time a wonder and a miracle to be seen among the clergy, that the bird had learned perfect music in nine notes, not by nature's dictation, but only by human art, and instead of the almost forgotten natural song often repeated only this in the admiration of the congratulating and beholding people. As the Experimentator says, the domesticated blackbird eats meat contrary to its nature and sings sweeter because of this. In winter it can hardly fly because of its fat. It likes to bathe itself and clean his feathers with his beak. Even though it is black and ugly, because of the pleasantness of its voice it moves itself into the affection of the mind. The blackbird does not shed its feathers like other birds, as Pliny says. Some say it is called a blackbird, because it flies alone, that is, mera. Its body is occupied by blackness. Although it is black in all regions, yet in Achaia it is white. Pliny: Blackbirds, woodpeckers, and partridges clean themselves annually with the bay leaf. The blackbird turns from black to red, sings in summer, stammers in winter. Every year its face changes into whiteness. - [Badke translation/paraphrase]