Male bowerbirds in Australian cities are raiding human trash to impress females, and the results are striking. City birds in Townsville, Queensland collected an average of 90 decorations each for their bowers. One bird gathered more than 300 items. Their rural counterparts averaged just 20.
The findings come from a new study published in the journal Royal Society Open Science by researchers at the University of Exeter. The team monitored the bowers of 61 male great bowerbirds across two sites in northern Queensland during the September through December 2023 breeding season. One site was the urban Townsville City. The other was the rural Dreghorn Cattle Station.
Male great bowerbirds build intricate tunnels from twigs, then collect colorful objects to display to visiting females. When a female enters the bower, the male throws an object into her view, shows off the plumage on the back of his head, then throws another object. The routine repeats until she either stays or leaves.
Caitlin Evans, from the Centre for Ecology and Conservation at Exeter's Penryn Campus in Cornwall, described what the researchers found at urban sites. "Once a female arrives and stands in the bower, males throw an object into their view and then display the plumage on the back of their head, then throw another object—and so on. Our findings show that bowerbirds in a city use a wide range of items scavenged from humans. Glass, plastic and wire were common choices, but 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."
The researchers photographed bower decorations from above in both visible and ultraviolet light. Bowerbirds can see in the UV range, so the team analyzed the items from the perspective of a female bird's vision, which is more sensitive to color than human eyes. In urban bowers, red decorations were more vivid and green decorations were duller than those found in rural areas. The two most common urban items were green glass and red wire. In rural areas, green leaves and seeds topped the list, followed by green glass.
To test whether preference for human items was a product of exposure or genuine taste, the researchers ran a second phase of the study. They removed all existing decorations from each bower and built a mixed pile of 10 items from an urban bower and 10 from a rural one, then left each site for three days. Both urban and rural males strongly favored the human-made items when given a free choice.
Evans noted that even rural birds seek out human objects when they can find them. "Even in rural areas, birds find items made by humans. In this case, we think they raided the bins and garage of a farm—and also the bowers of other male bowerbirds."
The study did not measure whether females actually prefer the more striking urban displays. Evans said the males' behavior suggests they might. "Our study did not assess whether females favor the more striking items collected in urban areas, but the males' enthusiasm for gathering these items suggests this is likely."
Dr. Laura Kelley, also from the University of Exeter, said the broader consequences remain unknown. "Our study demonstrates that the availability of human items—often glass and plastic—is affecting the behavior of bowerbirds. We don't yet know whether this has any negative or positi" — the published excerpt ends there, leaving the question open.
