Recent studies have suggested that crows hide food because they think others will steal it – a complex intuition seen in only a select few creatures. Some critics have suggested that the birds might simply be stressed out, but new research reveals that crows may be gifted after all.
Last year, a researcher from the University of Groningen in the Netherlands spent seven months in bird cognition expert Nicola Clayton’s University of Cambridge lab in the United Kingdom studying Western scrub jays, a member of the crow family.
A Groningen team then developed a computer model in which “virtual jays” cached food under various conditions. Their model showed, they argued, that jays might be moving their food – or hiding it – not because they were reading the minds of their competitors, but simply because of the stress of having another bird present and of losing food to thieves.
This contradicted work by Clayton’s group that suggested crows might have an awareness of other creatures’ mental states – a cognitive ability known as “theory of mind” that has been claimed in dogs, chimps and rats.
So Clayton and grad student James Thom decided to test the stress hypothesis. First, they replicated earlier work on scrub jays by letting the birds hide peanuts in trays of ground corn cobs – either unobserved or with another bird watching – and later giving them a chance to rebury them. As in previous studies, the jays hid a much higher proportion of the peanuts if another bird could see them: nearly twice as much as in private, the team reports in PloS One.
Then came the stress test. The jays were given trays with the ground cobs but no food to hide – a “sham” session. In a second session, they gave the birds new hiding trays and bowls of peanuts to hide. When the jays were done, the experimenters removed the trays and stole all of the peanuts. After a short break, researchers gave each bird another round of food, a new tray to hide it in, and one of the trays it had seen earlier: either the sham tray or the ransacked “pilfer” tray. The jays had 10 minutes for re-caching.
If the Groningen model was correct, Clayton argues, the stress of discovering food was missing from the pilfer tray ought to drive jays to stash more peanuts than those presented with the sham tray. In fact, there was no difference, even though crows have excellent memories for hidden food and remarkable abilities to find it again. The hypothesis that jays have “theory of mind” remains on the table, Thom says.