Read about this in a science magazine that wanyas gave me. Pretty cool.

The great bowerbird's taste for interior design seems quite Spartan compared to his relatives. He creates an avenue of sticks leading up to a courtyard, decorated with gray and white objects, such as shells, bones and pebbles. The male performs in the courtyard while the female watches from the lined avenue. Her point of view is fixed and narrow, and according to Endler, the male knows how to exploit that.

He found that the males place the largest objects towards the rear of the courtyard and the smallest objects in the front near the avenue. This creates forced perspective. From the female's point of view, the bigger objects that are further away look to be the same size the smaller objects that are close by. If bowerbird vision is anything like humans, the courtyard as a whole looks smaller to a watching female...

There are many possible benefits to this illusion. Endler says, "The simplest hypothesis (and perhaps most likely) is that the more regular pattern on the court, as seen from the avenue, makes the male more conspicuous or easier to see". Alternatively, by performing on an apparently smaller stage, the male could also make himself look relatively bigger to the female. "To my knowledge no other animals make constructions which produce perspective," says Endler.