Pliny the Elder [1st century CE] (Natural History, Book 10, 20; 10, 41; 10, 50; 10, 64): [Book 10, 20] here are also small birds with hooked claws, for instance the variety of woodpeckers called Birds of Mars that are important in taking auguries. In this class are the tree-hollowing woodpeckers that climb nearly straight upright in the manner of cats, hut also the others that cling upside down, which know by the sound of the bark when they strike it that there is fodder underneath it. They are the only birds that rear their chicks in holes. There is a common belief that when wedges are driven into their holes by a shepherd the birds by applying a kind of grass make them slip out again. Trebius states that if you drive a nail or wedge with as much force as you like into a tree in which a woodpecker has a nest, when the bird perches on it it at once springs out again with a creak of the tree. Woodpeckers themselves have been of the first importance among auguries in Latium from the time of the king a who gave his name to this bird. One presage of theirs I cannot pass over. When Aelius Tubero, City Praetor, was giving judgments from the bench in the forum, a woodpecker perched on his head so fearlessly that he was able to catch it in his hand. In reply to enquiry the seers declared that disaster was portended to the empire if the bird were released, but to the praetor if it were killed. Tubero however at once tore the bird in pieces; and not long afterwards he fulfilled the portent. [Book 10, 41] It is said that Mars's woodpecker is not found in the district of Taranto. [Book 10, 50] The [nest] of the woodpeckers hangs by a twig at the very end of the boughs, like a ladle on a peg, so that no four-footed animal can get to it. [Book 10, 64] Nature has also bestowed ... a tufted crest on Mars's woodpecker... - [Rackham translation]

Aelianus [170-230 CE] (On the Characteristics of Animals, Book 1, 45): The bird 'woodpecker' derives its name from what it does. For it has a curved beak with which it pecks oak-trees, and deposits its young in them as in a nest; and it has no need at all of dry twigs woven together or of any building. Now if one inserts a stone and blocks up the entrance for the aforesaid bird, it guesses that there is a plot afoot, fetches some herb that is obnoxious to the stone, and places it against the stone. The latter in disgust and unable to endure the smell springs out, and once again the bird's caverned home lies open to it. - [Scholfield translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 7:47): The woodpecker [picus] took its name from Picus, the son of Saturn, because he would use this bird in augury. People say this bird has a certain supernatural quality because of this sign: a nail, or anything else, pounded into whatever tree the woodpecker has nested in, cannot stay there long, but immediately falls out, where the bird has settled. This is the Martius woodpecker [picus], for the magpie [pica] is another bird. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Birds 5.105): Pycus martius is a small bird, as he says [i.e. Liber rerum], that penetrates trees with its bill. When woodpeckers strike the bark of trees, they understand that there is food underneath. Pliny: They rear chicks in the hollows of trees, into which trees when someone sends an arrow or something like that, the spike is immediately driven out by a certain grass, whatever force it may have taken. Having hooked claws, it rarely rests on the rocks, lest its claws be dulled. Many of their kind are black like blackbirds and yellow like orioles, but they are more beautiful and larger that are ruffed on the top of the head, rosy on the breast, green around the neck, blue on the wings, and sparkling on the tail. The Pycus martius is said to not live in the Tarentine fields. It is proper for them to lose their feathers once every year, namely at that time, as Pliny says, when the turnip is sown. The Experimentator says in a verse about the woodpecker: Little talkative bird, I greet you with a voice: If you do not see me, you will deny that I am a bird [Thomas has here confused the pica (magpie) with the picus (woodpecker) in this quote from Martial]. - [Badke translation/paraphrase]