Hiding behaviour of the scrub jay: more stress than smarts?

The fact that scrub jays continually move their food from one hiding place to another (known as recaching) does not necessarily imply subtle social intelligence on their part – it could simply be due to stress. PhD student Elske van der Vaart discovered this, together with her supervisors Charlotte Hemelrijk and Rineke Verbrugge, with the aid of a computer model. Their study was published on 1 March 2012 in the scientific journal PLoS ONE. Science journalist Michael Balter also writes about their research in the 1 March 2012 issue of Science.

Nearly all birds belonging to the corvid or crow family hide food underground, storing it for later. However, when fellow corvids see something being buried, they enjoy stealing it. The Western scrub jay (Aphelocoma californica), a blue-grey jay home to the southern USA, is well known for its smart little tricks to avoid being robbed.

Social intelligence

The scrub jay trick is as follows: if it notices other birds watching, it buries its worms as far away as possible and keeps recaching, over and over again, as if attempting to confuse the spies. As soon as it is on its own, it recaches its worms one more time. This behaviour appears so smart that speculation has it that the scrub jays are able to put themselves in another scrub jay’s position, and that they are able to come up with a line of reasoning on what others see and know, for instance: ‘If my fellow scrub jay knows where I’ve hidden the worm, I need to hide it again, somewhere else.’ This would be very special, as this is an ability only attributed to humans and perhaps some monkeys.

Stress

Van der Vaart and her supervisors, however, have developed an alternative theory which explains the birds’ behaviour without making much reference to social behaviour: a scrub jay may know from experience that its worms are safest if they are hidden far away from any other birds. If other birds are watching while a scrub jay hides its food and if it then keeps recaching it, this may very well not be due to the fact that it is trying to mislead the other birds, but because it is becoming stressed by their presence. It may perhaps be thinking: ‘I need to hide more worms for later!’ When at last the scrub jay is on its own again, it turns out that the jay itself is the one really confused by all the moving: many worms are no longer where the jay expects them to be. The result is that the bird becomes even more stressed and continues to move worms.

Virtual bird

Van der Vaart developed this theory using a corvid computer model that she had designed earlier to study corvid memory and learning behaviour. In essence, she created a ‘virtual bird’. The PLoS ONE article describes how in experiments this virtual bird displays the same recaching behaviour as a real jay, and of course without any extensive insight into what other jays are thinking. Science reports that empirical researchers are planning to test the predictions made by the computer model. This should ultimately lead to true understanding of the so often admired scrub jay intelligence.

Note for the press

- Contact: Elske van der Vaart, Artificial Intelligence and Theoretical Biology departments, tel. 050-363 8779, e-mail: e.e.van.der.vaart rug.nl or Prof. Charlotte Hemelrijk, Behavioural Ecology and Self Organisation, Center for Ecological and Evolutionary Studies, tel. 050-363 8084.
- Corvid Re-Caching Without Theory of Mind: A Model , Elske van der Vaart, Rineke Verbrugge & Charlotte Hemelrijk. PLoS ONE (2012), 7: e32904. doi: 10.1371/journal.pone.0032904
- 'Killjoys' challenge claims of clever animals, Michael Balter. Science (2012), 335: 1036-1037. doi: 10.1126/science.335.6072.1036