The garbage bins of Australia are giving researchers the chance to study an incredible example of an “interspecies innovation arms race”, according to a new paper.

Back in the 1930s, Australia was plagued with emus. The birds were causing such nuisance and damage that the army was, eventually, called in to deal with things. This is how the country found itself in 1932 in a peculiar situation: they were, in effect, at war with an indigenous bird species. A war that would be carried out by three men and two machine guns.

Now, the land down under seems to be embroiled in a new avian conflict, continuing their tradition of being at odds with birds. This time, the war is being fought between exasperated locals and sulphur-crested cockatoos (Cacatua galerita) — and it’s being fought in trash bins.

​”If we don’t close the bin right after throwing out the rubbish they’ll be in there,” said Ana Culic, 21, manager of the Loaf Cafe in Stanwell Park, a town near Sydney. ​”Cockatoos everywhere. Like, just rubbish all over the front area.”

​”They’re evolving. Yeah, like if you go back like five-ten years ago, they didn’t know how to open bins so they’re figuring stuff out,” said the cafe’s chef, 42-year-old Matt Hoddo.

You might recognize a sulphur-crested cockatoo should you see one. These white, yellow-crested birds make for intelligent, popular, but demanding pets all around the world. In Australia they can be very numerous, so much so, in fact, to be considered pests. They can grow up to 55 cm (17.5–21.5 in) in length, with those in Australia typically growing larger than those of the subspecies from New Guinea and nearby islands.

The new study reports on how these birds have figured out how to operate the lids on household bins. According to the authors, this behavior seems to have spread through direct observation from a single bird (or a small number of individuals) that first figured out how to do so. In essence, the research suggests that the birds in Sydney and the surrounding region have now developed their own tradition of bin-diving.

And now, they seem to be adapting further by learning to bypass the series of increasingly-creative ways locals are trying to prevent them from reaching their trash. This is a previously-unexplored example of an “interspecies innovation arms race,” the authors conclude.

Sightings revealed that a single cockatoo will open a bin by lifting the lid with its beak from the front edge. From there, while still holding, it will walk backward towards the hinge, which eventually forces the lid to flip open. An earlier study revealed that knowledge of this technique spread as other birds looked on, creating local “traditions”.

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Faced with their trash constantly strewn about their streets, the locals tried to adapt. Culic explains that her family first tried to scare the cockatoos away using owl statues, with no results. Then they tried to physically block the birds from opening the bins by placing bricks on the lids — but the birds learned how to push them off. So now they’ve resorted to drilling a lock in place to secure the lids.​ Other locals report similar stories, explaining that the birds have managed to work around bricks, large rocks, or elastic cords keeping the lids secure.

​”When we first started looking at this behavior, we were already amazed because actually the cockatoos learned how to open the bins,” said the study’s lead author Barbara Klump, a behavioral scientist at the Max Planck Institute in Germany.”I was really astonished by how many different methods people have invented,” she said.

This back-and-forth between the two species represents ​a “stepwise progression and reiteration” in which both are trying to adapt to the adaptation of the other.

So far, a census of 3,283 families revealed that some cockatoos could bypass low-level protections such as rubber snakes or bricks. However, they don’t yet seem able to deal with stronger methods such as the attachment of weights directly to the lid or sticking objects such as sneakers into the hinge to prevent birds from fully opening the bin.

Although the cockatoos don’t really stand a chance of ultimately coming out on top in this arms race, the team is excited to see what the interaction holds in store for us next. It may be easy for people to underestimate just how much work is required to protect their trash, and some people are already starting to relax their guard as cockatoos are becoming less active in their areas.

That being said, the team is convinced that the interaction between the birds and locals is unlikely to lead to the emergence of a new species. ​”They have a certain capacity to problem solve, and we know they are super curious and they like to explore,” Klump said. “But I don’t think that protecting the bins will in itself then make the cockatoos smarter.”

The paper “Is bin-opening in cockatoos leading to an innovation arms race with humans?” has been published in the journal Current Biology.

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