Why silver's parrot screams pieces of eight?

From the novel 'Treasure Island by Robert Louis Stevenson: Long John Silver to Hawkins on the parrot; "She's been at Madagascar, and at

Malabar, and Surinam, and Providence, and Portobello.

She was at the fishing up of the wrecked plate ships. It's

there she learned 'Pieces of eight,' and little wonder; three hundred and fifty thousand of 'em, Hawkins!"