Bowerbirds benefit from optical illusion

Male Great Bowerbirds use optical tricks commonly found in films and architecture to make themselves appear larger to potential mates, new research published this week inCurrent Biologysuggests.

Bowerbirds are famed for their courtship rituals in which males build complex "bowers" that are carefully decorated with attractive pebbles and flowers. These structures take many hours to build, with twigs woven together like thatch. The better the bower, the more likely the male is to attract a female partner.

But it now appears that the Great Bowerbird, native to Australia, has more tricks up its sleeve. New research suggests that the male birds carefully place their decorative objects such that those closer to the female admirer's viewing position are larger and those closer to the male suitor are smaller, thus making the male appear larger in relation to his surroundings.

The research group, led by John Endler from Deakin University in Australia, even tried moving the male bowerbirds' carefully-placed decorations to reverse the perspective, but the determined males had returned the objects to the familiar size order within 3 days. The next step in this group's research will be to confirm that this special arrangement has a direct influence on mating success.

Regardless, it appears that the Great Bowerbird takes advantage of a technique known as "forced perspective" sometimes used in films and architecture. For example in the recent "Harry Potter" films, Hagrid the giant is filmed with considerably smaller props than other characters in order to make his character appear larger in comparison. And in architecture, the same principles can be used to make a staircase look longer and more impressive by making it increasingly narrower as it rises.

This is the first time that the use of such complex visual tricks has been recorded in animals other than humans, and it is yet another feather in the cap for the intelligent bird-brains.