photo credit: University of Auckland
By Matthew Owens
Research published today (Wednesday) in the open-access academic journal PLOSONE shows that New Caledonian crows may have an understanding of causal logic that surpasses that of young children.
The international team from the University of Auckland and the University of Cambridge used a newly developed experimental paradigm based on Aesop’s fable The Crow and the Pitcher to test the birds’ causal understanding of water displacement. Aesop’s famous allegory tells the story of a thirsty crow that, unable to push over a pitcher of water, cunningly drops stones into the water raising the level high enough to drink from. Their findings suggest that the corvids have a sophisticated understanding of causality that is not seen in humans until between 5 and 7 years.
“It is rather exciting to find that these performances rival those of children between the ages of 5 to 7,” said Dr Alex Taylor, an Auckland University lecturer in the School of Psychology. “However, we don’t yet know if the crows are using the same cognition as children of these ages to solve these tasks.”
Far from bird-brained, New Caledonian crows are renowned for their cognitive gymnastics, both using and manufacturing tools in their natural habitat; skills that are correlated with larger brain volumes. In fact, the corvids have exceptionally large brains for their size and their largest brain regions are the very same that are implicated in learning and motor activity in humans. The crows routinely fashion digging tools by snapping small twigs and tearing up pandanus leaves to hoik out insects from crevices.
There are well-described cases of primates such as chimpanzees and orang-utans using tools in complex ways but other species also do this: Bears scratch their backs with trees, sea otters use stones to crack open sea food on their bellies, dolphins wrap scraps of sponge around their noses when hunting on the sea bed and elephants use branches to keep pesky flies at bay. It’s important to point out here that actually making tools is a much rarer activity than simply using them. The New Caledonian crow makes and uses tools with such elegance, sophistication and speed that they have no equal in the animal kingdom.
“The tools made by New Caledonian crows are certainly very impressive,” said Sarah Jelbert, lead author on the study. “They are the only species besides humans known to craft hooks in the wild.”
Furthermore, these birds are the only known non-human to make tools from materials not encountered in the wild and can also pass on this new information within cultural groups. This ability to make new tools from unfamiliar objects was originally discovered by Oxford University scientists observing a crow couple (Abel and Betty) in an experiment where both had to choose between a straight and hooked wire to lift a bucket containing food. After Abel had flown away with the hooked wire, Betty immediately started bending the remaining straight wire into a hook with her beak and successfully retrieved a bucket full of food from a pipe. Neither bird had ever come across malleable wire before.
In the new research Dr Taylor’s group captured 6 wild crows and ran them through 6 experiments testing their knowledge on how water is displaced by sinking objects.
“The idea behind this set of experiments is to use a ‘signature testing’ approach (looking at the pattern of passes and failures) to investigate what these birds can understand about causality.” Explains lead author Sarah Jelbert.
Because the birds are not accustomed to dropping stones in water or on prey, they were first trained to drop stones into a tall tube of water that brought up their cube of meat reward into beak’s reach. In the experimental tasks, the birds were able to very rapidly learn to drop stones into water rather than sand, plump for heavy rather than light objects, solid and not hollow and worked out that dropping stones into a tube with high as opposed to low water would get them their reward. Interestingly, the birds failed one test where dropping stones into a more efficient narrow versus wide tube was the ‘correct’ response. “Thus these crows appear to have a sophisticated, but incomplete causal understanding of displacement,” Said Dr Taylor.
The six experiements that put the New Caledonian crows through their paces.
Crucially a control task tested the extent to which perceptual cues and learning alone could account for the birds’ behaviour. The task was counter-intuitive in that dropping stones into one of 2 side tubes would raise the water level in a central tube via a sneaky connecting tube that was hidden from view. “The birds all failed, showing no sign that they could learn this over twenty trials.” It could be that their folk physics of how the world should work prevented them from using other cues and feedback to learn the task.
Dr Taylor’s work was recently featured in the BBC’s Inside the Animal Mind series, where a single bird dubbed ‘007’ was put through its paces when it had to solve a complex puzzle.
007 managed to complete the ‘mission impossible’ (eight separate steps in correct order), which was comprised of:
- Pulling a stick free tied to a string
- Using the stick to retrieve out-of-reach stones from 3 separate boxes
- Depositing the 3 stones into a Perspex box to collapse a floor that released a larger stick
- Using the large stick to retrieve food positioned more than beak’s reach in a final box
The BBC documentary Inside The Mind shows the remarkable cognitive ability of the birds.
Presenter and wildlife expert, Chris Packham says on the programme, “I’ve never ever seen anything like it. Of all of the bird behaviours I’ve seen, nothing matches that.”
Although the behaviour of the New Caledonian crows is remarkable, it is still unclear whether the birds are using the same cognitive processes as children or whether it is truly unique as other members of the corvid family such as Jays are alos capabale of some intelligent behaviour. “In terms of really understanding their cognition,” says Sarah Jelbert, “we’re still at the early stages – much more research has been conducted with primates.” Dr Taylor added, “It is going to be fascinating to find out in the next few years if these crows really do have enhanced cognition due to their tool manufacturing abilities.”