The bowers aren’t nests for raising kids; they are bachelor pads designed to attract and seduce one or more mates. When a female arrives to inspect the bower, the male struts and sings. He hopes to convince her to enter the bower, where mating takes place. The female then flies off to build a nest close by, leaving the male to try to convince another female to join in a romantic tryst. This male was picking up red articles. You can see a red shoelace in the foreground. Good luck to him.
See next to see his mating display.