Sources : Dyomeda

Pliny the Elder [1st century CE] (Natural History, Book 10, 10.126): Nor will I pass by the birds of Diomede. Juba calls them Plungers-birds, also reporting that they have teeth, and that their eyes are of a fiery red color but the rest of them bright white. He states that they always have two leaders, one of whom leads the column and the other brings up the rear; that they hollow out trenches with their beaks and then roof them over with lattice and cover this with the earth that they have previously dug from the trenches, and in these they hatch their eggs; that the trenches of all of them have two doors, that by which they go out to forage facing east and that by which they return west; and that when about to relieve themselves they always fly upwards and against the wind, These birds are commonly seen in only one place in the whole world, in the island which we spoke of as famous for the tomb and shrine of Diomede, off the coast of Apulia, and they resemble coots. Barbarian visitors they beset with loud screaming, and they pay deference only to Greeks, a remarkable distinction, as if paying this tribute to the race of Diomede; and every day they wash and purify the temple mentioned by filling their throats with water and wetting their wings, which is the source of the legend that the comrades of Diomede were transformed into the likeness of these birds. - [Rackham translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 7.28): Diomediae are birds named from the companions of Diomedes; fables say that his companions were transformed into these very birds. They are similar to coots in shape, the size of a swan, white in color, with large hard beaks. They are found near Apulia on the island Diomedia, flying between the crags of the shore and the rocks. They distinguish between their own people and foreigners. [Book 12, 7:29] If someone is Greek, they come up close and fawn on him, but if someone is of alien birth, they attack and wound him by biting, grieving as if with tearful voices either their own transformation or the death of their king – for Diomedes was slain by the Illyrians. - [Barney, Lewis, et. al. translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 2.45-50): [Chapter 2.45] There is an island which watches the shore of Apulia which is famous for the tomb and shrine of Diomedes. Also, here alone nest Diomedes’ birds; these birds cannot be found anywhere else, which can be judged remarkable. Their shape is almost the same as that of a coot; they are white in color, their eyes are fiery, and they have toothed bills. [Chapter 2.46] They fly about in flocks, which, for purposes of proceeding efficiently, are not without order. There are two leaders who rule the onrush: one goes in front of the column and the other brings up the rear — the former that he might lead a direct route and the latter that he might urge on the tardy. This is the discipline of their traveling. [Chapter 2.47] When the time for fructifying comes upon them, they dig trenches with their bills, and stretch shoots over the top, imitating the framework of a basket. Thus they cover up the space hollowed out underneath. Lest these lids be found wanting, and the wooden hollows carried away by chance winds, the birds press down the pile with the earth they dug out when raising their wells. [Chapter 2.48] They build their nests with double entrances. It is not done fortuitously -- they mark out the entrances and exits according to the regions of the heavens. The opening that dismisses them to the feeding grounds is open to the east, and that which receives them is situated towards the west; thus, light rouses them, and does not deny them for their retreat. For the relieving of their bellies, they fly upwards in adverse winds, so their bodily discharges may be blown further away from them. [Chapter 2.49] They judge between visitors. Those who are Greek they permit to approach, and as far as it is to be understood, they fawn coaxingly upon them as countrymen. If they are of another race, they rush upon them and attack. They frequent the sacred shrine every day, and their zeal takes this form: they wet their feathers with water, and they flock together with thoroughly soaked and dewy wings. By shaking off the moisture, they purify the shrine. Then they clap their wings and depart, as though they have completed their worship. [Chapter 2.50] Because of this, the birds are said to have been Diomedes’ companions. Certainly, before the advent of the Aetolian leader, they did not go by the name of Diomedes, but thenceforth they have been called thus. - [Arwen Apps translation, 2011]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Birds 5.41): Dyomedes are birds, which are so called from king Dyomedes, as Solinus says. The Greeks call them herodios. They are the size of a swan, colored white, and have fiery eyes and a toothy mouth. They fly in flocks; the first in line leads the flock, while the last keeps those in the rear and the middle in line [also said of the crane]. With their beaks they dig stones out of the earth to make their nests, and then, by placing the branches on top of them, they imitate a roof of lattices, that is, the roofs of cupolas; and in order that the winds may not carry away the house, they compress the dust which they had accumulated when they were digging their nests. The exits or entrances are determined by the quarters of the sky; the one they exit from is oriented towards the east, and returnees are welcomed through the west entrance. When they mourn with tearful voices, they signify either either their own transformation or the destruction of the king. Solinus and Jacobus: If a Greek approaches them, they are flattering; but they attack those of other nations with bites. - [Badke translation/paraphrase]