Bowerbirds Use Geometry to Woo Females

Sometimes love is an illusion. Especially if you're a bowerbird.

These crow kin from Australia and New Guinea are known for constructing elaborate edifices to woo mates. But males of one species, the great bowerbird (Ptilonorhynchus nuchalis), go a step further: They use a trick of architectural perspective to boost their allure, and will stick to their own scheme even if it falls short with the females.

While most bowerbirds embellish their "love nests" with bright, shiny baubles, the great bowerbird's decor is comparatively bland: an avenue of sticks leading to a pair of courts garnished with mostly gray-to-white objects like pebbles, shells, and bones.

But a lack of color doesn't mean a lack of style for these birds. Biologists John Endler and Laura Kelley of Australia's Deakin University have found that male great bowerbirds carefully arrange their courts' decorations in a specific pattern, with bigger items farther away from the bower avenue (where the female stands), creating the illusion of an evenly textured stage.

This effect—called "forced perspective"—may be visually pleasing to the female, or it may simply make the male, who waves colored objects during his mating dance, easier to see. Whatever the reason, the males who build the most geometric patterns also have the most success in winning mates.

What's most surprising is the commitment of each male to his own aesthetic. As reported in today's Proceedings of the National Academy of Sciences, when the scientists rearranged objects in the birds' courts to make the patterns stronger, the suitors restored their original design within three days.

It seems that, for birds as for humans, sometimes getting your own way counts most.