PREVIEW

BY MARK WORGAN

Male Australian bowerbirds have a new kink - stealing human items including handcuffs in a desperate bid to impress a mate.

The birds build elaborate structures known as bowers from twigs before decorating them with colourful items to attract visiting females.
Researchers from the University of Exeter compared decorations collected by great bowerbirds in Townsville, Queensland, with those gathered by birds in a nearby rural area.

They found that urban males amassed larger and more colourful collections, with most decorations originating from human sources, while their rural counterparts relied on more natural materials.

“Bowers are built exclusively to attract a mate, and males choose decorations that contrast against their own plumage and the bower itself,” said Caitlin Evans, from the Centre for Ecology and Conservation at the University of Exeter’s Penryn campus in Cornwall.

“Once a female arrives and stands in the bower, males throw an object into her view and then display the plumage on the back of their head, before throwing another object and repeating
the sequence.”

Evans said the study revealed that urban bowerbirds made use of a remarkable variety of items scavenged from human environments - including, in a raunchy twist, handcuffs.

“Glass, plastic and wire were common choices, but we also found objects including a pair of handcuffs, medicine jars at bowers near a hospital, and fluorescent mouth guards from a site close to an Australian Rules football ground,” she said.

The study found that red decorations used in urban bowers were more vivid than those in rural settings, while green decorations were generally less vibrant.

Researchers examined the bowers of 61 male birds from the perspective of a female bowerbird, using established evidence about their vision, which is more sensitive to colour than that of humans.

Although the study did not investigate whether females preferred the more striking urban displays, Evans said the males’ determination to collect such items suggested they may offer an advantage.

Urban males gathered an average of around 90 decorations, compared with about 20 for rural birds. One city-dwelling male collected more than 300 objects for his bower.

Where human-made items are unavailable, male bowerbirds typically use natural materials such as fruit, seeds, leaves and sticks.

The most common decorations found in urban areas were green glass and red wire, while rural birds most frequently used green leaves, seeds and green glass.

“Even in rural areas, birds find items made by humans,” Ms Evans said. “In this case, we think they raid the bins and garage of a farm – and also the bowers of other male bowerbirds.”

In a second phase of the research, scientists presented 20 objects – 10 from an urban bower and 10 from a rural one – to both urban and rural males. Both groups showed a strong preference for human-made items.

Dr Laura Kelley, also of the University of Exeter, said the findings highlighted the growing influence of human activity on wildlife behaviour.

“Our study demonstrates that the availability of human items – often glass and plastic – is affecting the behaviour of bowerbirds,” she said.
“We do not yet know whether this has a positive or negative impact on the birds, but it serves as a reminder that human activity is altering the natural world in unexpected ways.”

The research was partly funded by the Natural Environment Research Council GW4+ Doctoral Training Partnership and has been published in the journal Royal Society Open Science.

The paper is titled Urbanization Alters Courtship Signals in Male Great Bowerbirds.