Saw these at a local nursery, The Great Outdoors, a few evenings ago.
They were lightweight, probably plastic fence posts. The decorations seemed to be decoupaged, covered with heavy lacquer. Some were birdhouses, others were capped. All were whimsical and expensive. The least expensive being around $200. The taller ones, depending on the amount of decoration, climbed to over $300.
I'm sure someone here will figure out how to make them! I'm thinking PVC round pipe would work as well.