Why is there a wren on a farthing?

Why is there a wren on a farthing?

King Edward eventually gave in on the question, fearing that such designs would be unacceptable to the British people, but non-heraldic themes for the halfpenny (a sailing ship) and farthing survived. The selected design for the farthing, a wren, placed the smallest British bird on the British coin smallest in value.