Wild Cockatoos and Humans Compete for a Rubbish Prize in a Potential ‘Arms Race’

Sulfur-crested Cockatoos in eastern Australia have learned to open trash cans. Their human neighbors are fighting back.

It’s trash day—the best day of the week for Sulfur-crested Cockatoos in southern Sydney. Within the past decade, Australia’s native parrots have figured out, and taught each other, how to open trash can lids. It takes some effort, but by stretching their legs, extending their necks, and tight-rope walking along the edge of a can, cockatoos can successfully use their beaks to flip open the hinged lids that are standard in Sydney’s suburbs. 

Today, though, there is some trouble. One trash can owner has placed a brick on the lid to deter cockatoos. But ultimately it’s no sweat for this bird. Standing on the bin’s edge, she pushes the brick with her beak until it falls off the edge. Then she flips the lid and reaches in, tossing out trash to uncover last night’s leftovers: bread and pizza. Once she’s had her fill, she hops to the bin next door. 

Scientists first documented the cockatoos’ clever behavior eight years ago when Richard Major, an ornithologist at the Australian Museum Research Institute in Sydney, filmed a cockatoo opening a bin and shared it with colleagues. Fascinated, the scientists wanted to know how cockatoos learned this new trick. Publishing their findings in Science in 2021, they showed that Sulfur-crested Cockatoos, which are native to forests of eastern and northern Australia, have developed this skill not only once but multiple times. Geographically separated cockatoo populations have different bin-opening techniques; once one bird figures out how to flip the lid, other birds in the area watch and learn.

This week, in Current Biology, a team published a follow-up study that focuses on the human side of the equation. The researchers documented more than 50 strategies that people employed to keep cockatoos out of trash bins. They suggest the conflict could be the beginning of an “innovation arms race,” where humans and cockatoos develop increasingly imaginative ways of outsmarting each other to control access to garbage cans. “For some of the protections, the cockatoos actually learn how to defeat them, and then people come up with better, more effective methods,” says lead author Barbara Klump, a behavioral ecologist at the Max Planck Institute of Animal Behavior. “People actually socially learn from other people, especially their neighbors, about how to protect the bins.”

While the birds are beautiful, they have become unwelcome pests in the neighborhoods. “The homeowners don’t like [the cockatoos] because they have to go and clean up the streets,” says co-author Damien Farine, a social evolutionary ecologist at the University of Zurich. In southern Sydney, people can’t simply get new trash cans or lock their bins shut—the cans are custom fit to the municipality's garbage-truck model and the lids must swing open when the truck flips the cans upside down. So, to be rid of the messy birds, garbage-can owners began testing some defensive strategies of their own.

Klump decided to study their responses. Researchers visited four suburbs, documenting 3,283 bins, and surveyed an additional 1,134 people from 401 suburbs. They discovered that, like cockatoos, people learn the best strategies from each other: 172 people protected their bins and 64 percent used social information when choosing a strategy, such as placing rocks and bricks on lids, shoving shoes and sticks in hinges to jam them shut, and tying ropes to prevent lids from flipping all the way open. Some even purchased and installed a commercially sold bin hook ($30 USD). Attaching a weight beneath the lid works best, says John Martin, an applied ecologist at Western Sydney University who participated in the research, since the cockatoos are not as strong as a garbage truck.

The researchers aren’t concerned about the impact of pawing trash on the birds’ health. Sulfur-crested Cockatoos are not considered a species of concern by the International Union for the Conservation of Nature, and human leftovers are not their only food source. Garbage cans are put out only once a week, so the birds mostly eat seeds and plants. Still, the cockatoos have found a way to exploit the human environment and “spoil themselves once a week with fast food,” Martin says.

Researchers believe the conflict could be the beginning of an innovation arms race. In human warfare, arms races occur when each side tries to outmaneuver the others’ weapons and defenses. Nature has arms races, too. When parasitic cuckoos lay eggs in other host species’ nests, for example, the egg color and pattern laid by both species tend to evolve as each attempts to outplay the other. The potential cockatoo arms race has a unique quality. “This is the first time that one of these arms races have been described, as far as we know, to involve humans as well,” Farine says.

To be certain an arms race is occurring, the researchers must first understand in greater detail how cockatoos teach each other to open bins. New strategies for opening bins need to be learned among birds, not invented on the spot, to be considered an arms race. That's the "final piece of the puzzle" to figure out, Klump says.

Antonio Osuna Mascaró, who studies tool use in cockatoos at the University of Veterinary Medicine, Vienna, was not involved in this study and isn’t convinced yet that it’s a true arms race. Cockatoo social learning is less advanced than in humans, he says, and the birds could be learning these strategies individually. “Each time that a cockatoo finds a solution to one of these problems is by individual innovation—that would be my bet.” He suggests the researchers investigate how cockatoos learn to open more heavily armored bins.

Further study of human and wildlife conflict could surface other instances of arms races. Martin hopes this study will inspire more research of this nature. “I think there's a lot of examples out there that haven’t been investigated,” he says.

There might already be one underway in Toronto, says animal behaviorist Suzanne MacDonald at the University of Toronto, who was not involved in the new study. She says raccoons like to paw through the trash in her city, which has already deployed special anti-raccoon trash cans. Because people are much more intelligent than raccoons, she says it's an arms race the city can win. 

MacDonald seems to have more faith in Australia’s scrappy birds, known for being clever. In the escalating fight over garbage, she says, “I’m on team cockatoo."