I know what you are thinking John E Marriott/Getty

Fears over surveillance seem to figure large in the bird world, too. Ravens hide their food more quickly if they think they are being watched, even when no other bird is in sight.

It’s the strongest evidence yet that ravens have a “theory of mind” – that they can attribute mental states such as knowledge to others.

Many studies have shown that certain primates and birds behave differently in the presence of peers who might want to steal their food. While some researchers think this shows a theory of mind, others say they might just be reacting to visual cues, rather than having a mental representation of what others can see and know.


Through the peephole

Thomas Bugnyar and colleagues at the University of Vienna, Austria, devised an experiment to rule out the possibility that birds are responding to another’s cues. The setup involved two rooms separated by a wooden wall, with windows and peepholes that could be covered.

First, a raven was given food with another raven in the next room, with the window open or covered, to see how quickly it caches its prize. With the window open, the birds hid their food more quickly and avoided going back to conceal it further.

Then individual ravens were then trained to use the peephole to see where humans were putting food in the other room. The idea here was to allow the bird to realise it could be seen through the peephole.

Who’s in the next room?

Finally, they gave ravens food with the window covered but the peephole open, and played sounds from a speaker in the next room so that the raven might think another bird was there.

Just try to steal my food Jana Mueller

In the last setup, the ravens hid their food more quickly – within around 8 seconds rather than 14 – than they did when the window and peephole were both covered, and returned less often to conceal the stash. Both, presumably, in fear of being seen by a peeping rival that may steal that food later on.

The results suggest ravens can generalise from their own perceptual experience to infer the possibility of being seen by others who are not visibly present.

Not unique to humans

“This proves they have a basic understanding of seeing, which is a basic form of a theory of mind,” says Bugnyar. “This basically means that some non-human animals can indeed evolve this particular ability of attributing a mental state to another one, which has always been considered to be one of the unique human abilities.”

Bugnyar thinks that ravens’ complex social lives, involving both cooperative and competitive relationships, created strong evolutionary pressures that have selected for this ability.

Corvids – the family of birds to which ravens and crows belong – routinely hide food to eat later, and have to make sure they aren’t seen by rivals who might steal their cache.

Theory of mind

Nicola Clayton at the University of Cambridge, UK, says the study is beautifully designed, but so far no single study has shown unequivocally that any animal has theory of mind.

“It’s a case of converging evidence to bear on a problem,” she says. “But this study comes as close as any to showing so.”

Martin Schmelz at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, says the study refutes a major argument against previous studies and shows exciting social cognitive abilities in ravens for the first time.

“Ravens in this study are shown to attribute visual access to others, which is certainly one aspect of a theory of mind,” he says. “They don’t have a human-like full-fledged theory of mind, but the authors are also not claiming this.”

Journal reference: Nature Communications, DOI: 10.1038/ncomms10506

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