Divination - particularly skilled in ornithomancy (interpreting omens from birds).
Calchas was a great seer in Greek mythology; in Homer's Iliad he makes the prophecy that Chryseis must be returned to Troy, triggering the rift between Achilles and Agamemnon. He also features in Sophocles' Ajax, Quintus of Smyrna's Posthomerica and the lost epic Cypria.
Some sources say that Calchas died of shame after being defeated by Mopsus; others say that he died of laughter after he heard a (supposedly) incorrect prediction of his death. (Source - Wikipedia)
The date given - 1300 B.C. - is merely conjecture, of course. This is the date of the earliest recorded telling of the tale of Jason and his voyage to recover the Golden Fleece, a story in which Mopsus, Calchas' contemporary, figures in a small way.