When Barbara Klump ran into homeowners on trash-collection day, she would tell them that something very special was happening in their suburb of Sydney. She meant the birds. The big white ones?, the residents asked. The birds that are always opening trash cans and making a huge mess? Yes, those, the sulphur-crested cockatoos. The trash-raiding behavior that was annoying the suburban homeowners had also brought Klump, a behavioral ecologist at the Max Planck Institute of Animal Behavior, all the way from Germany to Australia. To someone like her, this behavior was an incredible discovery.
It wasn’t just that the sulphur-crested cockatoos were opening heavy plastic trash cans; it was that the flocks were in the process of learning how to do it. Before Klump’s study began in 2018, the behavior had been reported in only three suburbs around Sydney. By the time the study wrapped up in 2019, the bin-opening trend had spread to 44 suburbs. “It’s pretty amazing,” says Alice Auersperg, a bird-cognition researcher at the University of Veterinary Medicine Vienna, who was not involved in the study. “You see innovation spreading.” The birds were learning from one another.
Klump and her colleagues liken the spread of trash-bin opening to a form of bird “culture,” with regional “subcultures” in which different groups of cockatoos in different suburbs have subtly different techniques for opening trash cans—not unlike the way a dance craze mutates as it gains popularity.
Sulphur-crested cockatoos are a species of parrot native to Australia. They’re snowy white, with a crest of bright yellow atop their head. Domesticated ones have, as parrots famously do, sometimes learned to imitate human speech. Wild ones have thrived in Australia’s human-altered landscape, where they are as ubiquitous as pigeons are in North America. Richard Major, a biologist at the Australian Museum and co-author on this study, got interested in the species’ trash foraging when he saw a sulphur-crested cockatoo memorably gnawing on a chicken drumstick. Then one day in 2016, he was driving to work near Sydney when he spotted another cockatoo eating out of an open trash bin. He stopped to investigate, which spooked the bird away. But once Major closed the trash bin and got back to his car, the bird immediately flew back to the bin and opened it with its beak, continuing its interrupted meal. Major managed to film it on his phone.
“I guess my initial reaction was ‘Who’s a clever cockie,’” Major told me in an email, “but my mind immediately jumped to the image of the drumstick-muncher.” Now, was this bin-opening cockatoo especially clever, or was everyone doing it? Major had come across bin-openers before, but this was the first time he’d caught one on film. He shared the video with Lucy Aplin, with whom he was already collaborating on a study tracking the social structure of sulphur-crested cockatoos and who heads up the Max Planck lab where Klump now works. Aplin and Klump were both fascinated by Major’s video. The scientists devised an online survey for residents around Sydney to report trash-bin-opening behavior, which allowed the team to cover a far larger area than the scientists could alone. In 2018 and 2019, Klump and her colleagues traveled to Australia to observe more closely for themselves.
To distinguish between individual cockatoos, they lured the birds with sunflower seeds and dabbed small dots of nontoxic paint on their back. This was easy, Klump told me, because the cockatoos are so fearless around humans and because they’re so white. Then, the scientists drove around neighborhoods on trash-collection day and watched.
Being able to open a trash bin turned out to be a relatively rare skill: Only nine of 114 identifiable birds they observed could do it. Most that tried, failed. The trash lids are heavy, after all. To successfully pull off the maneuver, the cockatoos have to stand on the bin’s edge, lift the lid with their beak, and then carefully walk toward the hinge while still holding the lid. Most of the successful bin-openers—89 percent—were males, which may be because they tend to be socially dominant and physically stronger than females.
To study the behavior’s spread, the team analyzed how bin-opening techniques varied from bird to bird, neighborhood to neighborhood. Some birds, for example, held the lid with their beak, while others held it with their beak and left foot; some shuffled along the edge of the bin, while others put one foot in front of the other. “Little, little details,” Klump said, but they add up to each population having “their idiosyncratic way of how to do things.” Klump and her team believe that the spread of bin opening is an example of social learning, in which one bird is copying another and then another copies that one and so on. The end result is many variations on a theme.
Only one other parrot species has been studied opening trash cans: New Zealand keas, which were discovered opening bins behind a hotel in the 2000s. Ludwig Huber, an animal-cognition researcher also at the University of Veterinary Medicine Vienna who studied those keas, told me that he thinks the New Zealand birds were emulating one another rather than imitating one another This is a key distinction in social learning: Imitation is about copying exact physical movement, and emulation is seeing an outcome (for example, a trash-bin opening) and figuring how to get there by oneself. Which is happening in sulphur-crested cockatoos? Klump and her colleagues found that bin-opening technique was most similar among birds geographically close to one another, which suggests imitation, but Huber isn’t entirely convinced. Ideally, he said, “you would need to have a naive observer who has never attempted to open the bin and would have the opportunity to see a demonstrator and then afterward try again.” In other words, you would have to see the entire learning process for a single bird. “But this is difficult of course,” he added, at least out in the real world. Controlled experiments inside a lab might shed some light on this fundamental question about how animals learn from one another.
It’s not surprising that birds adapting to suburban life might come up with new behaviors, though. “A lot of parrots have a lot of time on their hands,” says David Lindenmayer, a biologist at Australian National University. In fact, he told me, a flock of sulphur-crested cockatoos visits acacia trees in his yard every year when the nuts ripen. Once they eat their fill, they spend their time trimming little branches off the acacia trees. It’s not clear why they do it, but, Lindenmayer observed, “they have 10 or 12 hours to fill.” No wonder some birds are landing on trash cans and lifting their lid, just to see what’s underneath. They’ve learned that bountiful meals are sometimes hidden inside.
Klump and her team plan to keep tracking the spread of this bin-opening behavior. They weren’t able to go to Australia this year or last because of the coronavirus pandemic. But the resident surveys are still running, and she hopes to go back soon—and to see if this very annoying yet profound trash-bin-opening behavior has spread or evolved even more in the past two years.
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