A sulphur-crested cockatoo opening a wheelie bin does not simply flick up a loose lid. The bird grips the edge with its beak, raises the heavy plastic, holds or repositions it, then shuffles along the narrow rim until the lid can be forced past its balance point. Only then can the flock reach the food inside.

Before 2018, residents had reported the behaviour in only three suburbs in the Sydney and Wollongong region. By late 2019, reports came from 44. The trick did not appear randomly across the map. It moved preferentially into neighbourhoods close to places where bin-opening cockatoos were already present.

A 2021 paper in Science concluded that social learning drove most of that spread. Direct observations added a second layer: birds in different places developed distinct ways of completing the task. In the behavioural-science sense, the cockatoos were not merely solving the same problem. They were establishing local foraging cultures.

A difficult route to discarded food

Sulphur-crested cockatoos are common across eastern Australia and increasingly comfortable in cities. Household bins present them with a rich but concealed food source. The container is familiar and widely available; getting into it is the hard part.

The successful sequence requires several coordinated decisions. A bird must find a workable grip, lift against the lid’s weight, prevent it falling shut, move its body while balanced on the bin and push the lid far enough to flip it open. Bread and other scraps become accessible only after that chain succeeds.

The research began after Australian Museum ornithologist Richard Major filmed a cockatoo opening a bin near his home and shared the footage with behavioural ecologist Lucy Aplin. As the Max Planck Institute’s account of the project explains, Barbara Klump, Aplin and colleagues then designed a study that worked at two scales: public reports across hundreds of suburbs and close observation of identifiable birds at selected hotspots.

Their peer-reviewed paper, published on 23 July 2021, called the behaviour a putative cultural adaptation to an urban environment. That cautious wording matters. This is one study, not settled consensus about every cockatoo population, and animal culture is a technical category rather than a claim that the birds possess a human social world.

How 1,396 reports became a diffusion map

The team ran online surveys in 2018 and 2019, asking residents whether they had seen cockatoos open household bins, where the sighting occurred and when they first remembered it happening. The Australian Museum’s research summary describes the two-year public survey; in total, 1,322 participants supplied 1,396 reports across 478 suburbs.

There were 338 positive reports from 44 suburbs. To reduce the risk that one mistaken sighting would put a suburb on the map, a positive area required at least two reports. Before 2018, that threshold was met in only three suburbs. By the end of 2019, it was met in 44.

The researchers divided the reported chronology into seven periods. They then used network-based diffusion analysis, linking suburbs according to geographic distance and known cockatoo movement. If each local population had discovered bin opening independently, new occurrences need not have clustered around places where the behaviour was already established. If birds were learning from nearby birds, neighbourhood position should predict adoption.

Models containing social transmission received overwhelming statistical support. The best model estimated that social learning accounted for the behaviour reaching 93.9 per cent of the positive suburbs, with a 95 per cent confidence interval from 86.5 to 97.3 per cent.

That is a model estimate, not a record of researchers watching the first demonstration in every suburb. The survey also relied partly on residents remembering when they first saw the behaviour. The team included reporting effort, suburb size and number of dwellings as possible alternative influences, but citizen-science data cannot make uneven noticing disappear entirely.

Why an inherited trick does not fit the pattern

The title’s contrast with genetic inheritance needs to be stated carefully. Genes clearly matter to the species’ abilities. They help build a strong curved beak, dexterous feet, a social life and a brain capable of sustained exploration and learning.

What genes do not readily explain is this geographical sequence. Sulphur-crested cockatoos already lived across the study area, and standard wheelie bins were broadly available. Yet bin opening was initially local, then appeared sooner in neighbouring suburbs than in distant ones. A new genetic variant could not plausibly sweep through dozens of urban groups on that map and timetable.

Multiple cockatoos were present in 93.3 per cent of reported opening events, providing abundant opportunities to watch. The statistical spread, the restricted starting points and the birds’ local techniques all point towards knowledge moving socially.

Social learning does not necessarily mean deliberate teaching or exact imitation. A bird may be drawn to a bin by another bird, notice which part of the lid moves, repeat a productive action or learn through its own attempts after watching access become possible. The study established a socially structured diffusion pattern. It did not identify one exclusive psychological mechanism inside every learner.

This is related to the distinction in ScienceBlog’s account of Seattle crows learning a dangerous human face. In both cases, information persisted beyond the animals involved in the first event. That persistence can arise through observation and group response without anyone intending to give a lesson.

The opening sequences acquired local accents

To move from a map of reports to the behaviour itself, the researchers temporarily marked 486 cockatoos with small paint dots at three hotspots. The marks allowed individual recognition and disappeared when the feathers were replaced during moult.

Video analysis covered 160 successful bin-opening sequences. The team divided the task into five stages and recorded the available variations at each one. Birds could differ in where they gripped, whether they used a foot, whether they first pried at the lid, which direction they walked and how they completed the flip.

Some differences were strongly individual. Walking direction, possibly influenced by a bird’s preferred side, and unnecessary prying were more consistent within a bird than between birds. Other components, particularly actions during the opening stage, differed more strongly between sites.

Even after the analysis accounted for individual identity, successful sequences grew less similar as the geographic distance between observations increased. Birds near one another tended to solve the task in related ways. The authors described those clusters as local subcultures.

Not every difference has to be copied. Body size, experience, bin condition and individual preference can also shape a movement. The cultural inference comes from the pattern across many sequences: location explained part of the variation after the same individual performing a familiar routine was considered.

A minority opened the bins

The survey tracked where the behaviour existed; it did not imply that every cockatoo in a positive suburb could perform it. At Stanwell Park, the team marked more than 90 per cent of the local birds and obtained detailed demographic information.

Only nine of 114 identifiable cockatoos completed a successful opening. Another 27 attempted the task without succeeding. Both juveniles and adults opened bins, but 89 per cent of successful birds whose sex was known were male. Higher-ranking males were more likely to attempt and succeed.

Strength and access may help explain that imbalance. Male sulphur-crested cockatoos tend to be heavier and socially dominant, and observers saw birds displacing one another from bins. A profitable technique can be socially available without being equally easy or worthwhile for every group member to perform.

Most birds did not need to master the full sequence to benefit. Once a skilled individual opened a bin, nearby flock members could join the meal. Culture here was therefore not a city in which every cockatoo held the same knowledge. It was a social system in which a small number of capable openers could provide both food and demonstrations.

The spread included a second invention

The map was not one uninterrupted wave radiating from Sydney’s south. The diffusion model identified a likely independent innovation in Narraweena, in northern Sydney, during late 2018. From there, the behaviour spread into nearby areas through the same socially structured process.

This does not weaken the cultural interpretation. Innovations can be invented more than once. Culture determines whether a useful act vanishes with its inventor or becomes available for others to acquire, modify and maintain.

The distinction also prevents a romantic but inaccurate story about one genius cockatoo teaching an entire city. The evidence supports at least two origins followed by neighbourhood diffusion. It does not identify the first bird at the original southern sites, nor show that all 44 suburbs inherited one perfectly preserved technique.

That evidential standard is much stronger than a single episode of possible copying. ScienceBlog’s earlier piece on a dolphin calf handling its mother’s bailer shell described an observation consistent with transmission but unable by itself to prove culture. The cockatoo work combined geographical spread, repeated behaviour, identified individuals and local variation.

Culture can alter the human environment in return

The bins were not passive experimental apparatus. Residents disliked having rubbish scattered across streets and developed countermeasures. A 2022 follow-up in Current Biology documented bricks, filled water bottles, ropes, sticks and commercially available devices used to stop the lids opening.

People also learned from neighbours. As one technique failed, some residents escalated to another, producing what the researchers cautiously called a potential interspecies innovation arms race. The cockatoos’ culture altered human behaviour, which changed the problem the birds then faced.

The original finding was not that Sydney’s cockatoos had all become master thieves. It was that one complex and profitable skill could arise, travel through a social landscape and develop local forms quickly enough to watch.

Genes made bin opening possible. Sydney’s streets, bins and discarded food made it worthwhile. The route from three suburbs to 44 was carried largely by cockatoos paying attention to other cockatoos.