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Humans and parrots battle in an ‘arms race’ over trash in Australia

In the suburbs of Sydney, garbage bins are the front lines of a messy battle between humans and birds. On one side are raven-size dumpster-diving parrots called sulfur-crested cockatoos;  on the other are homeowners who’d like to stop cleaning up after the sloppy eaters. In a new study, researchers detail the arms race between pillaging parrots and frustrated residents, noting both sides appear to learn tricks from their peers.

Such competitions aren’t exactly uncommon in places where animal and human habitats overlap, “but this paper provides the data to show what’s happening both on the human side and the wildlife side, which is often lacking,” says Sarah Benson-Amram, a cognitive ecologist at the University of British Columbia, Vancouver, who was not involved in the new study. “To see that all together is fantastic.”

Australia’s cockatoos have a taste for trash. To access their favorite snacks, such as bits of old bread or scraps of ham sandwiches, the bright white birds use their curved beaks and feet to pry bin lids open. After helping themselves to a trash buffet, they toss away anything unappetizing, leaving trash strewn about.

In a previous study, Barbara Klump, a behavioral ecologist at the Max Planck Institute of Animal Behavior, and her colleagues showed how the birds pick up successful tricks from one another—say, how to knock a loose brick off a bin—thus passing on a kind of dumpster diving culture.

Now, she and colleagues turned their scientific gaze to the “human side of the cockatoo story.” They surveyed more than 3000 trash bins in four Sydney suburbs, recording residents’ defensive techniques and grouping them into categories. People can’t seal the bins shut because the lids need to tilt open when garbage trucks pick them up. So, the locals have gotten creative at parrot-proofing, Klump says. Some strategies involved no alteration to the bin itself, such as putting up rubber snakes. Others involved placing loose bricks or spikes atop the lid. Some strategies prevented lids from easily flipping open, such as shoving shoes or pool noodles into the hinges. Finally, some homeowners permanently attached heavy weights, such as filled water bottles, to the lid. This tactic proved most successful at keeping the clever cockatoos out.

Like the parrots, humans learned from their neighbors, as the researchers discovered by asking more than 1000 people how they devised their cockatoo control methods. Of the 172 people who said they guarded their trash, 64% said they picked their tricks up from someone else, researchers reported on 12 September in Current Biology. Residents of the same street often practiced similar strategies. “There was an element of social learning involved,” Klump says.

With members of each species working together to outwit the other, this garbage-fueled arms race seems primed to intensify, the researchers note, as humans strengthen their defenses and cockatoos coordinate to circumvent them.

The cockatoos seem up to the challenge. The researchers observed them knocking loose bricks and rocks from trash bins and squeezing through restricted openings.

Such arms races are preferable to lethal approaches to controlling wildlife, says Lauren Stanton, a cognitive ecologist at the University of California, Berkeley. “Cockatoos and other urban animals are simply trying to survive in the new environments we have created,” says Stanton, who was not involved with the new study. “As urbanization continues to bring us closer to wildlife, innovating ways to coexist will be critical for us all.”

Benson-Amram agrees and recommends Sydney homeowners vary their strategies frequently to keep cunning cockatoos from cracking the code. “I find it delightful that wildlife keeps us on our toes,” Benson-Amram says. “The best strategy for us is to keep innovating.”

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