28 August 2004

(54) Quoth The Raven

Now, it seems, even the bird-brained have theories of mind

HUMANS like to regard themselves as exceptional. Other animals do not have complex, syntactical languages. Nor do most of them appear to enjoy the same level of consciousness that people do. And many philosophers believe humans are the only species which understands that others have their own personal thoughts. That understanding is known in the trade as having a “theory of mind”, and it is considered the gateway to such cherished human qualities as empathy and deception.

Biologists have learned to treat such assertions with caution. In particular, they have found evidence of theories of mind in a range of mammals, from gorillas to goats. But two recent studies suggest that even mammalian studies may be looking at the question too narrowly. Birds, it seems, can have theories of mind, too.


In the Proceedings of the Royal Society, Bernd Heinrich and Thomas Bugnyar of the University of Vermont, in Burlington, describe a series of experiments they have carried out on ravens. They wanted to see how these birds, which are known to be (at least by avian standards) both clever and sociable, would respond to human gaze.

Response to gaze is reckoned to be a good measure of the development of theory of mind in human children. By about 18 months of age most children are able to follow the gaze of another person, and infer things about the gazer from it. Failure to develop this trick is an early symptom of autism, a syndrome whose main underlying feature is an inability to understand that other people have minds, too.

To test whether ravens could follow gaze, Dr Heinrich and Dr Bugnyar used six six-month-old hand-reared ravens, and one four-year-old. The birds were sat, one at a time, on a perch on one side of a room divided by a barrier. An experimenter sat about a metre in front of the barrier. The experimenter moved his head and eyes in a particular direction and gazed for 30 seconds before looking away. Sometimes he gazed up, sometimes to the part of the room where the bird sat, and sometimes to the part of the room hidden behind the barrier. The experiment was videotaped.

Dr Heinrich and Dr Bugnyar found that all the birds were able to follow the gaze of the experimenters, even beyond the barrier. In the latter case, the curious birds either jumped down from the perch and walked around the barrier to have a look or leapt on top of it and peered over. There was never anything there, but they were determined to see for themselves.

A suggestive result, but not, perhaps, a conclusive one. However, the second study, carried out by Dr Bugnyar when he was working at the University of Austria, and published last month in Animal Cognition, suggests that ravens may have mastered the art of deception too.

In this case, the observation was serendipitous. Dr Bugnyar was conducting an experiment designed to see what ravens learn from each other while foraging. While doing so he noticed strange interactions between two males, Hugin, a subordinate bird, and Munin, a dominant one.

The task was to work out which colour-coded film containers held some bits of cheese, then prise the containers open and eat the contents. The subordinate male was far better at this task than the dominant. However, he never managed to gulp down more than a few pieces of the reward before the dominant raven, Munin, was hustling him on his way. Clearly (and not unexpectedly) ravens are able to learn about food sources from one another. They are also able to bully each other to gain access to that food.

But then something unexpected happened. Hugin, the subordinate, tried a new strategy. As soon as Munin bullied him, he headed over to a set of empty containers, prised the lids off them enthusiastically, and pretended to eat. Munin followed, whereupon Hugin returned to the loaded containers and ate his fill.

At first Dr Bugnyar could not believe what he was seeing. He was anxious about sharing his observation, for fear that no one would believe him. But Hugin, he is convinced, was clearly misleading Munin.

As it happened, Munin was no dummy either. He soon grew wise to the tactic, and would not be led astray. He even stooped to trying to find the food rewards on his own! This made Hugin furious. “He got very angry”, says Dr Bugnyar, “and started throwing things around.” Perhaps ravens have something else in common with people—a hatred of being found out.

From The Economist, May 2004