City Trash Is Changing How These Birds Woo Mates

Australia’s Most Stylish Bird Has Found a Way to Turn Litter Into a Courtship Advantage

In northern Queensland, Australia, male great bowerbirds are doing something remarkable with the litter humans leave behind, and it may be giving their courtship displays a real visual boost.

Great bowerbirds are among nature’s most elaborate decorators. Instead of flashy feathers or a powerful song, males win over mates by building and decorating structures called bowers, tunnel-like arrangements of sticks surrounded by carefully chosen objects. More decorations, and more visually striking ones, generally means more mating success. A new study published in Royal Society Open Science found that males living in cities are stocking their bowers with plastic, wire, glass, and other human-made trash, producing a bigger, bolder display than anything their rural counterparts can pull off with sticks and leaves alone.

Human pollution isn’t just cluttering city streets. It’s actively reshaping how wild animals compete for mates. When researchers gave both city and country bowerbirds a choice between urban and rural decorations in a controlled experiment, males from both sites strongly favored the urban stuff.

How City Trash Becomes Bowerbird Treasure

Researchers from the University of Exeter studied 61 bowers across two field sites in northern Queensland during the birds’ 2023 breeding season. One site was in Townsville, where males built in parks and gardens. The other was at Dreghorn Cattle Station, a rural site where males built in eucalyptus woodland.

Urban bowers held, on average, about 93 decorations each. Rural bowers averaged roughly 20. That’s nearly five times as many, and city bowers were also physically larger on average. While rural birds were mostly working with green glass, natural leaves, and seeds, city birds were loading up on green glass, red wire, green plastic, and metal pieces. Decorations on urban bowers were far more likely to be human-made, about 89% of the time compared to roughly 46% for rural bowers.

Seeing the World Through a Bowerbird’s Eyes

To understand whether these differences actually matter to female bowerbirds, the researchers used a visual model based on bowerbird vision, which includes ultraviolet light, a wavelength invisible to humans. Decoration photographs were processed through software that converts images into something closer to what a bowerbird perceives, accounting for the four types of color-detecting cells in their eyes.

Red decorations in urban areas registered as significantly more color-saturated, meaning more vivid in their redness, than red decorations in rural areas. Green decorations told the opposite story: rural greens were brighter and more saturated than urban ones. Natural green plants in cities appear to be less vibrant than those in wild habitats, meaning even the natural materials urban birds find aren’t as visually impressive as what rural birds can access. City life hands bowerbirds a windfall of vivid reds and larger objects, but with a trade-off in the quality of greens available.

Given the Choice, It’s No Contest

To figure out whether display differences came down to preference or simply what was available, the researchers ran a direct experiment. They collected decorations from both urban and rural bowers, cleared each bird’s bower, and placed a mixed pile of urban-sourced and rural-sourced decorations nearby. After three days, males from both city and country sites were about 10 times more likely to select urban decorations. An urban-sourced decoration had about a 77% predicted chance of being selected, compared with about 25% for a rural-sourced decoration.

A separate test used only decorations collected from rural bowers, which included a mix of natural and human-made materials. Even within that rural pile, males were about 10 times more likely to grab the human-made items. Rural males were actually slightly more biased toward human-made materials than urban males in this test.

Rural birds simply don’t have access to the kinds of materials they’d prefer to use. It’s not a difference in taste between city and country birds. It’s a difference in what’s lying around.

What Bowerbirds Reveal About Animals in a Human World

Bowerbirds have reportedly been incorporating human-made materials into their bowers since at least 1899, according to records cited in the paper, and their use has only grown as such materials spread further into the environment. That’s over a century of birds quietly adapting to human waste, and it raises a bigger question about how deeply urban sprawl is rewiring animal behavior.

Not all of it is benign. Wire and string can trap and injure birds, and entanglement has proven fatal in other urban-nesting species. Plastic ingestion has been linked to harmful effects in other bird species too, and bowerbirds may face similar risks, though that remains an open question for future research.

For now, the male great bowerbird living near a city appears to have an advantage in building a bigger, more eye-catching display, not because of anything it evolved, but because humans keep throwing things away. It’s an accidental gift from a species that has no idea it’s giving one. Whether that translates to more mates is something scientists still don’t know.

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