From Kook Science

Alectryomancy (from the Greek: ἀλεκτρυών, alectryon ["cockerel, rooster"] + μαντεία, manteia ["divination, soothsaying"]) is a method of divination based on the interpretation of the peckings of a sacred cockerel. On the subject, Lewis Spence in his Encyclopædia of Occultism (1920), p. 13, relates the following:

Alectryomancy, or Alectormancy: An ancient method of divination with a cock. In practising it, a circle must be made in a good close place, and this must be divided equally into as many parts as there are letters in the alphabet. Then a wheat-corn must be placed on every letter, beginning with A, during which the depositor must repeat a certain verse. This must be done when the sun or moon is in Aries or Leo. A young cock, all white, should then be taken, his claws should be cut off, and these he should be forced to swallow with a little scroll of parchment made of lamb-skin upon which has been previously written certain words. Then the diviner holding the cock should repeat a form of incantation. Next, on placing the cock within the circle, he must repeat two verses of the Psalms, which are exactly the midmost of the seventy-two verses mentioned under the head of "Onimancy," and it is to be noted on the authority of an ancient Rabbi, that there is nothing in these seventy-two which is not of some use in the kabalistical secret. The cock being within the circle, it must be observed from which letters he pecks the grains, and upon these others must be placed, because some names and words contain the same letters twice or thrice. These letters should be written down and put together, and they will infallibly reveal the name of the person concerning whom inquiry has been made; it is said, though the story is doubted, that the magician Iamblicus used this art to discover the person who should succeed Valens Caesar in the empire, but the bird picking up but four of the grains, those which lay on the letters T h e o, left it uncertain whether Theodosius, Theodotus, Theodorus, or Theodectes, was the person designed. Valens, however, learning what had been done, put to death several individuals whose names unhappily began with those letters, and the magician, to avoid the effects of his resentment, took a draught of poison. A kind of Alectromancy was also some-times, practised upon the crowing of the cock, and the periods at which it was heard.

Ammianus Marcellinus describes the ritual which accompanied this act rather differently. The sorcerers commenced by placing a basin made of different metals on the ground and drawing around it at equal distances the letters of the alphabet. Then he who possessed the deepest occult knowledge, advanced, enveloped in a long veil, holding in his hand branches of vervain, and emitting dreadful cries, accompanied by hideous’ convulsions. He stopped all at once before the magic basin, and became rigid and motionless. He struck on a letter several times with the branch in his hand, and then upon another, until he had selected sufficient letters to form a heroic verse, which was then given out to the assembly. The Emperor Valens, informed of this circumstance, was ill-pleased that the infernal powers should have been consulted regarding his destiny. Indeed, he went further, for with unexampled severity, he proscribed not only all the sorcerers, but all the philosophers jn Rome, and punished them so severely that many perished.

In the fourth song of the Caguet Bonbec, of Jonquieres, a poet of the fourteenth century, the details of an operation in Alectryomancy are exactly and curiously set forth.