What did Ernest find and how did he kill it in the classic The Swiss Family Robinson?

From the text:

"Have no uneasiness," said my wife, "this is not from our poultry-yard, it is a wild goose, killed by Ernest."

"It is a sort of penguin, I believe," said Ernest, "distinguished by the name of booby, and so stupid, that I knocked it down with a stick. It is web-footed, has a long narrow beak, a little curved downwards. I have preserved the head and neck for you to examine; it exactly resembles the penguin of my book of natural history."