Aristotle [ca. 350 BCE] (De animalibus Book 9, 20.1-2): The cuckoo, as it has been already observed, makes no nest, but lays its eggs in the nests of other birds, especially in that of the phaps, and in those of the sparrow and lark on the ground, and in the nest of the chloris in trees. It lays one egg, upon which it does not sit, but the bird in whose nest it lays both hatches the egg and nurses the young bird; and, as they say, when the young cuckoo grows, it ejects the other young birds, which thus perish. ... The cuckoo appears to act prudently in thus depositing her egg; for it is conscious of its own timidity, and that it cannot defend its young, and therefore places them under the protection of another bird, in order that they may be preserved; for this bird is very cowardly, and when it is pecked by even small birds, it flies away from them. - [Cresswell translation, 1887]

Pliny the Elder [1st century CE] (Natural History, Book 10, 11.27): The cuckoo seems to be made by changing its shape out of a hawk at a certain season of the year, as the rest of the hawks do not appear then, except on a very few days, and the cuckoo itself also after being seen for a moderate period of the summer is not observed afterwards. But the cuckoo is alone among the hawks in not having crooked talons, and also it is not like the other hawks in the head or in anything else but color: it rather has the general appearance of the pigeon. Moreover a hawk will eat a cuckoo, if ever both have appeared at the same time: the cuckoo is the only one of all the birds that is killed by its own kind. And it also changes its voice. It comes out in the spring and goes into hiding at the rising of the dog-star, between which dates it lays its eggs in the nests of other birds, usually wood-pigeons, for the most part one egg at a time, as does no other bird; it seldom lays two. Its reason for foisting its chicks on other birds is supposed to be that it knows itself to be hated by the whole of the birds, for even the very small birds attack it; consequently it thinks that a progeny will not be secured for its race unless it has escaped notice, for which reason it makes no nest; it is a timid creature in general. Therefore the brooding hen in the nest thus cuckolded rears the changeling. The young cuckoo being by nature greedy snatches the bits of food away from the rest of the chicks, and so gets fat and attracts the mother bird to itself by its sleek appearance. She delights in its beauty and admires herself for having borne such a child, while in comparison with it she convicts her own chicks of not belonging to her, and lets them be eaten up even under her own eyes, until finally the cuckoo, now able to fly, seizes the mother bird herself as well. At this stage no sort of bird will compare with a young cuckoo for savory flavor. - [Rackham translation]

Aelianus [170-230 CE] (On the Characteristics of Animals, Book 3, 30): The cuckoo is extremely clever and most adroit at devising ingenious solutions to difficulties. For the bird is conscious that it cannot brood and hatch eggs because of the cold nature of its bodily constitution, so they say. Therefore, when it lays its eggs, it neither builds itself a nest nor nurses its young, but watches until birds that have nestlings are flown and abroad, enters the strange lodging, and there lays its eggs. ... And if the nests are empty, it will not go near them, but if they contain eggs, then it mixes its own with them. But if the eggs of the other bird are numerous, it rolls them out and destroys them and leaves its own behind, their resemblance making it impossible to know them apart and detect them. And the aforesaid birds hatch the eggs which are none of theirs. But when the cuckoo's young have grown strong and are conscious of their bastardy, they fly away and resort to their parent. For directly they are fledged they are recognized as alien and are grievously ill-treated. - [Scholfield translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 7:67): The cuckoo [tucus], which the Spaniards call ciculus [cuculus], is named from its particular call. These birds have a proper season for their return migration, at which time they are taken up on the shoulders of kites because of their brief and small spans of flight, lest their strength fail, fatigued by the long expanse of sky. Cicadas are born from their saliva. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Birds 5.34; 5.71): [Thomas describes the cuckoo under the names cuculus and karkolaz.] [Birds 5.34] The cuckoo [cuculus], as he says [i.e. Liber rerum], is a wicked bird. It is so called from the sound of its voice. In singing it does not change its voice, but always repeats the same song. It has almost the same color as a turtledove, but it is aloof in nature. The bird is very lazy and unstable in place. It lays its eggs in the nest of a bird of another species, and reduces the number of eggs which it finds in another's nest to the number of eggs which it lays of its own, that is to say, lest, while the bird finds an excess of eggs in number, it should be rejected as if it were another's. A deceived bird, therefore, fosters an egg of a foreign species, and brings it forth, and is not so clever as to distinguish the size of the cuckoo chick from the smaller chicks. And so, as Pliny says, while the cuckoo chick is still sitting in the nest with the rest of the chicks and is weak, yet with natural greed it snatches food from the other chicks, and with this satiety it grows fatter than the rest and becomes more shiny. Seeing the cuckoo chick's elegance, the mother rejoices in its form, and marvels at herself that she has given birth to such a one. She condemns all her true children in comparison with it, and suffers herself to be carried away by its admiration. And this is its reward: the ignorant find ignorance. For when a cuckoo has been brought up by its mother and nursed to the strength to fly, the cuckoo in its turn rises up against the mother and destroys her. It enters either the hidden places of the earth or the hollows of trees, and there it accumulates food in the summer, and lives there in the winter. Pliny reports something about the cuckoo, not asserting it, but rather disproving the false beliefs of the Gentiles: It is another thing, he says, that they say about the cuckoo, a miracle: in the place where one hears the cuckoo for the first time, if the right foot is drawn around and the footprint is dug out, fleas will not be born wherever the soil is scattered. Isidore reports about the cuckoo, but very ambiguously: these, he says, are carried on the shoulders of kites because of their short and poor flight, so that they do not fail when exhausted by long distances in the air. The saliva of these generates cicadas. [Birds 5.71] Karkolaz is a bird of the East, naturally cunning and mischievous. As Aristotle says, for this one, loving idleness and wandering curiosity, is also slow in procreating its kind, but since nature cannot deny its full duty, when a female has received seed from a male and feels that her eggs are ripe for laying, she looks for a nest of another bird to lay them in. Thus the deluded bird fosters the eggs of a foreign race. - [Badke translation/paraphrase]