Male bowerbirds in Australian cities are increasingly decorating their mating structures with discarded human items – including wires, broken glass, cans and even handcuffs – to impress potential mates, according to new research.
Instead of relying on natural decorations like leaves, seeds, or fruit as they once did, birds are increasingly using a colorful assortment of human debris and everyday items, according to a study published in June by the University of Exeter in the UK.
Humpbacks—scientifically known as Ptilonorhynchidae—are songbirds found only in Australia and New Guinea and world-famous for their unique mating behavior, in which males construct elaborate structures called bowers out of branches on the ground, which they then elaborately decorate to attract females.
In a study published in the journal Royal Society Open Science, scientists compared collections of dozens of bowerbirds in the city of Townsville, Queensland, with collections of their relatives in rural areas.
They found that urban birds used significantly more objects, those with brighter colors, and most of them were of human origin.
What kind of garbage is the most popular?
Green glass fragments and red wire are particularly common. Researchers have also discovered unusual objects, such as handcuffs, medicine bottles near a hospital, and fluorescent face masks near a sports stadium.
One particularly industrious male collected over 300 items. Rural competitors averaged about 20 ornaments, while urban birds amassed around 90.
The mating ritual is quite complex: as soon as the female enters the bower, the male throws individual objects into her field of vision, simultaneously displaying his plumage. Bowerbirds have significantly more sensitive color vision than humans.
Rural birds are also attracted to human waste.
A further experiment also revealed a preference for colorful, human-made objects. Both urban and rural birds preferred human-made objects over natural materials such as leaves, seeds, or fruit. The researchers noted that it is unclear whether this preference for human-made objects will have a positive or negative impact on the birds in the long term.
It's also still unknown whether more attractive decorations actually improve a male's chances of finding a mate. "Our study didn't assess whether females prefer more eye-catching items collected in urban areas," said Caitlin Evans, a researcher involved in the study. "But the males' enthusiasm for collecting such items suggests that it's quite likely.".