crows and herons
Literal meaning: the birds themselves. Rarely used outside classical or poetic contexts.
In old waka poems, crows and herons are sometimes contrasted.
black and white (go stones); go (game)
Metonymic use: crows (black) and herons (white) refer to the black and white stones of go, and by extension the game itself. Found in classical go literature and set phrases like 烏鷺の争い.
The phrase 'crow-and-heron contest' is an elegant way to refer to a game of go.
Compound of 烏 (crow, black) and 鷺 (heron, white). The go-related meanings arise from the black and white stones used in the game.