NOT so long ago, the idea that birds might possess some form of what we call intelligence seemed quite ridiculous. Yet this view has changed dramatically in recent years, with numerous studies showing that some bird species are capable of complex cognition. Members of one family of birds in particular – the Corvidae, which includes crows, rooks and ravens – have an ability to make and use tools which is at least as sophisticated as that of chimpanzees.
Two new studies, published this week, provide yet more demonstrations of the remarkable cognitive abilities of this group of birds. One shows that Caledonian crows can use up to three tools in sequence to obtain food, the other that rooks can use stones to raise the level of water in a vessel in order to bring a floating worm into reach.
This study, by Joanna Wimpenny and her colleagues at the University of Oxford’s Behavioural Ecology Research Group, is the first demonstration of spontaneous sequential tool-use in a species other than humans. Sequential tool use is indiciative of an ability to plan ahead, but more research is needed to establish whether this behaviour is actually the result of rational planning, or merely of a process called chaining, whereby a series of stimuli evoke a sequence of responses. (However, the scrub jay, another member of the corvid family, has been shown to be capable of planning for the future.) These findings are published in the open access journal PLoS One.
The second study, by Chirstopher Bird and Nathan Emery of the University of Cambridge and Queen Mary University of London, respectively, is published today in Current Biology. Unlike crows, rooks have not been observed using tools in the wild, but this study clearly demonstrates that they are capable of solving a complex problem. The rooks used in the study also quickly learned to use large stones instead of small ones, and that sawdust cannot be manipulated in the same way as water.
The problem solved by the rooks is analagous to the one in Aesop’s fable, The Crow and the Pitcher:
A Crow, half-dead with thirst, came upon a Pitcher which had once been full of water; but when the Crow put its beak into the mouth of the Pitcher he found that only very little water was left in it, and that he could not reach far enough down to get at it. He tried, and he tried, but at last had to give up in despair. Then a thought came to him, and he took a pebble and dropped it into the Pitcher. Then he took another pebble and dropped it into the Pitcher. Then he took another pebble and dropped that into the Pitcher. Then he took another pebble and dropped that into the Pitcher. Then he took another pebble and dropped that into the Pitcher. Then he took another pebble and dropped that into the Pitcher. At last, at last, he saw the water mount up near him, and after casting in a few more pebbles he was able to quench his thirst and save his life.
Little by little does the trick.
Bird and Emery even suggest that the ancient Greek story-teller may have based his tale on a real observation. But in folklore, all members of the corvid family are referred to as crows, so if Aesop did indeed observe this behaviour, it may have been a rook that he saw.
For more on the cognitive abilities of birds, and more vids of crows doing incredibly clever things, see this post about avian intelligence.
Wimpenny, J. et al (2009). Cognitive Processes Associated with Sequential Tool Use in New Caledonian Crows. PLoS ONE, 4 (8) DOI: 10.1371/journal.pone.0006471.
Bird, C.D. & Emery, N. J. (2009). Rooks Use Stones to Raise the Water Level to Reach a Floating Worm. Curr. Biol. DOI: 10.1016/j.cub.2009.07.033.