It’s a bower bird performance centre. Quite literally. They make an area where they can perform for a mate.

They like the colour blue so collect heaps of blue things and decorate their bower with them.

This one has got a bunch of milk bottle caps, milk bottle cap rings, blue plastic straws and what look like pegs.

It sounds funny till you think about stuff that humans do for exactly the same reason (to be “interesting” to a prospective partner)