What do an Australian banknote, a fluorescent mouth guard and a pair of handcuffs have in common? No, it’s not some Australian Rules football-related bank heist. The answer is they are all items used by city-dwelling Australian bowerbirds to impress the local females.
Male great bowerbirds create intricate tear-shaped tunnels of twigs called bowers, which can be up to a metre long and half a metre tall. At one end, males place a collection of locally sourced, colourful items, which they then display to visiting females.
Research in Royal Society Open Science shows that males living in urban areas use a wide range of items which they scavenge 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,” says Caitlin Evans from the University of Exeter, who studied the birds.
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Evans and colleagues compared items collected by bowerbirds in Townsville City and a rural area, both in Queensland. Across 61 bowers, city birds gathered decorations that were larger and more colourful than those of their understated rural rivals. The items were mainly from human sources, and include dark green bottle glass, bright red wire and a crimson hair scrunchie.
Urban birds also collected more items – about 90 on average, compared to 20 for rural males. One particularly prolific urban bird gathered more than 300 items at his bower.
In really remote rural areas, where humans don’t make a mess, male bowerbirds typically collect fruit, seeds, leaves and sticks. In the rural areas that were studied here, the bowerbirds collected a mixture of natural and non-natural items, including green leaves and green glass.
“In this case, we think they raid the bins and garage of a farm – and also the bowers of other male bowerbirds,” says Evans.
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In a second phase of the study, the team collected ten items from an urban bower and ten items from rural one and presented them to both urban and rural males. Both groups favoured the human-made items.
Laura Kelley, also from the University of Exeter, says “Our study demonstrates that availability of human items – often glass and plastic – is affecting the behaviour of bowerbirds.” The consequences of this are currently unknown, but according to Kelley, it’s “a reminder of how human activity is changing the natural world in unanticipated ways.”
Top image: Great bowerbird. Credit: Caitlin Evans
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