Adult male bowerbird. Credit: Caitlin Evans.
Unlike their rural counterparts, male great bowerbirds in an Australian city use a range of often colourful human items to impress females.
The bowers in urban settings included human items such as glass and plastic to banknotes, and even a pair of handcuffs.
Male bowerbirds create an intricate tunnel of twigs called a bower, then gather colourful items to show to any females that visit.
The new study, by the University of Exeter, compared items collected by bowerbirds in Townsville City and a rural area, both in Queensland, Australia.
City birds gathered larger, more colourful decorations, mostly from human sources, than their more understated rural rivals.
Caitlin Evans, from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall, said: “Bowers are built exclusively to attract a mate, and males choose decorations that contrast against their own plumage and the bower itself.
“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.”
She added: “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.”
Typical bower built by male great bowerbirds in urban environments. Note the large number and variety of colourful decorations. Credit: Caitlin Evans.
Enthusiasm
In urban bowers, red decorations were more vivid and green decorations were duller than those found in rural areas.
The researchers examined bowers of 61 males from the perspective of a female bowerbird – using existing evidence on their vision, which is more sensitive to colour than human eyes.
Evans said: “Our study did not assess whether females favour the more striking items collected in urban areas, but the males’ enthusiasm for gathering these items suggests this is likely.”
Urban bowerbirds collected more items – about 90 on average, compared to 20 for rural males.
One urban bird gathered more than 300 items at his bower.
When human items are not present, male bowerbirds typically collect fruit, seeds, leaves and sticks.
In this study, the two most common decorations in urban areas were green glass and red wire, while the most common in rural areas were green leaves/ seeds and green glass.
Evans explained: “Even in rural areas, birds find items made by humans. In this case, we think they raid the bins and garage of a farm – and also the bowers of other male bowerbirds.”
Photo of a typical bower built by male great bowerbirds in rural environments. Credit: Caitlin Evans.
Favoured
In a second phase of the study, researchers collected 20 items – ten from an urban bower and ten from a rural one.
They presented these to both urban and rural males, and both groups strongly favoured human-made items.
Dr Laura Kelley, also from the University of Exeter, said: “Our study demonstrates that availability of human items – often glass and plastic – is affecting the behaviour of bowerbirds.
“We don’t yet know whether this has any negative or positive impact on them, but it’s a reminder of how human activity is changing the natural world in unanticipated ways.”
The paper, published in the journal Royal Society Open Science, is entitled: “Urbanization alters courtship signals in male great bowerbirds.”
