Bowerbirds Build Art. Females Grade It.

The male great bowerbird does not have bright plumage. It does not have an elaborate tail. What it has is a construction project, and the standards it is held to by the females that inspect its work are, by any measure, remarkable.

The bower is a structure of sticks built on the ground, forming an avenue that the male decorates with objects collected from the surrounding environment. Bones, shells, stones, berries, glass fragments, plastic bottle caps, anything pale or brightly colored gets incorporated into the display. The male arranges these objects in a specific spatial pattern, with larger objects placed farther from the bower entrance and smaller objects closer, creating a forced perspective illusion that makes the bower interior appear larger than it is when viewed from the female’s position at the entrance.

This is not accidental. When researchers experimentally rearranged the objects to disrupt the forced perspective, males returned and corrected the arrangement, restoring the gradient. The males understand, in some functional sense, how the display looks from the female’s point of view, and they maintain it accordingly.

John Endler at Deakin University has studied bowerbird aesthetics in detail, finding that the forced perspective illusion is consistent across individual males and that females prefer bowers with more accurate perspective gradients. The female is not just assessing the quantity of decorations. She is assessing the quality of the spatial arrangement, and the males that get it right mate more often.

The Theft Economy

Male bowerbirds steal decorations from each other’s bowers. A male that leaves his bower unattended risks returning to find his best objects gone, relocated to a rival’s display. The theft is selective, with males targeting the most valuable objects rather than taking indiscriminately. This creates a competitive economy of decoration in which the males with the best bowers attract the most females and also attract the most theft, requiring continuous maintenance and replacement.

Some males respond by hiding their best objects when rivals are nearby, a behavior that implies awareness of the rival’s intentions. Whether this constitutes genuine deception in a cognitive sense is debated, but the behavior is consistent with it.

The Female’s Assessment

A female great bowerbird visits multiple bowers before mating, spending time at each one assessing the display. She may visit the same bower multiple times over several days. The male performs a display inside the bower during her visits, holding objects in his bill and moving in specific patterns. The female watches from the bower entrance, and her decision to mate or leave is based on an assessment that integrates the quality of the bower construction, the quality of the decoration arrangement, and the quality of the male’s performance.

After mating, the female leaves and raises her chicks entirely alone. The male returns to maintaining his bower and attracting the next female. The bower is not a nest. It is purely a display structure, built and maintained for the sole purpose of being judged.

The bird that builds forced perspective illusions, that steals strategically, that is assessed by females applying aesthetic criteria that researchers have spent decades trying to fully characterize, is doing something that sits uncomfortably close to art. Whether it is art depends on definitions that science has not settled. The bower is real, the perspective gradient is real, and the female’s preference for it is real. What to call that is a separate question.