Male Satin Bowerbirds (like the bird on the right in this photo) build specialised stick structures, called bowers, and they decorate the area with blue objects. These objects can be natural, but in urban settings they are more often plastic. Females (like the other bird in this photo) visit these bowers, and based on their inspections choose which male they will mate with. These particular birds live in a place where there are many humans, so they aren't too worried about photographers like me.
Keith Horton