The Wrenboys and their song -

The wren, the wren, the king of all birds,
St Stephen's day was caught in the furze…

are a version of the mummers that are traditional all over Europe. The wren was used as a scapegoat for the troubles of the year past. The boys of the area went out and hunted these very common birds (then more common than now), which are tiny and look like teenshy men in tweed coats. When they had killed one it was fastened onto a branch of furze (the gorse plant of which it's said "when gorse is out of bloom, kissing's out of fashion", because its yellow, coconut-scented blossom is virtually always in flower), and paraded around - a ridiculous parody of long-ago scapegoatings.

For some reason these mummings in Europe mostly seem to be on St Stephen's Day (December 26); they always involve men thatched all over with straw and singing rhymes from house to house, playing jokes, and rhyming requests for money for drink or for food - "so up with the kettle and down with the pan, and give us a penny to bury the wren".