Male bowerbirds prefer to dazzle females with bright human-made items

Male bowerbirds are notorious for their complex mating rituals. They build intricate tunnels out of twigs—the bowers from which they get their name—and then decorate them with random colorful items gleaned from the environment. When a female of the species shows up to check out a male’s fancy digs, the male tosses his shiniest objects in her direction and shows off his plumage in hopes of impressing her.

According to a new paper published in the journal Royal Society Open Science by University of Exeter scientists, urbanization and the associated growing availability of brightly colored human-made items have had a significant impact on courtship display behavior in Australian male bowerbirds. There are marked differences in the choice of decorations for bowerbirds in urban versus rural environments. This might be because urban birds simply have greater access to the items than their rural counterparts, since birds in both environments show a marked preference for human items.

The University of Exeter researchers monitored the bowers of 61 male great bowerbirds in two sites in Australia’s northern Queensland—the rural Dreghorn Cattle Station and the urban Townsville City—during the prime breeding season (September–December 2023). Then they photographed the bower decorations in situ from above in both visible and UV light (bowerbirds can see in the UV range), using an umbrella to create diffuse lighting.

Next, they selected the 10 decorations closest to the bower entrance, since these were the most likely to be used by the male bird for his displays. These were also photographed and marked to identify the original source. Then the team removed all existing decorations from each bower and created a mixed slush pile of 10 randomly selected urban bowers and 10 randomly selected rural bowers, and they left the site alone for three days. Males were never offered any items from their own bower.

When the team returned to the sites, they determined which decorations had been selected from the slush pile and moved to a bower, and whether it came from an urban or rural source. After recording the data, all the original decorations were returned to their bowers.

Green glass and red wire

The subsequent analysis revealed that rural bowerbirds most often used green glass and green leaves or seeds for decoration, while urban birds preferred green glass and red wire. Plastic items were also popular, although “we also found items including a pair of handcuffs, medicine jars at bowers near a hospital, and fluorescent mouth guards from a site near an Australian Rules football ground,” said University of Exeter co-author Caitlin Evans.

Urban bower decorations were more than 10 times more likely to be human-made than those of rural bowers, which had more natural items, such as fruit, seeds, leaves, and sticks. Urban bowers also had nearly five times as many decorations as rural ones, averaging 90 items per bower compared to 20 for the rural birds. One overachieving urban male gathered 300 items to decorate his bower. Both urban and rural male bowerbirds showed a strong preference for human items when given a choice of items sourced from each environment. And red decorations in urban bowers were more vivid, and the green items duller, than in rural bowers.