Intelligent animals

I’ve just watched a fascinating Wildlife on Two documentary on the BBC about capuchin monkeys of Central and South America. This programme highlighted how intelligent these small monkeys are, in fact they have the largest brains relative to their body size of all the monkeys.

We’ve all seen footage of chimpanzees using twigs to fish out termites or to hunt in groups. These monkeys displayed similar or even more advanced evidence of intelligent behavour. For example:

• they have the ability to “imagine” that food may be hidden from sight, under bark for example, or are revealed by lowering water levels in the case of shellfish
• they use their tails to reach into deep water holes, an effective sponge that is longer than their arms
• some of their group appear to be more intelligent than others, and this is displayed by the group learning to ignore inappropriate warning signals from individual monkeys who cannot be relied upon – “the monkey who cried snake!”. They have particular warning signs for particular threats – at one point it showed them fleeing up a cliff-face from a hunting jaguar (Panthera onca), however, it wasn’t a simple retreat, once at the top they started throwing large rocks at the jaguar

During studies of the monkeys in captivity, they expressed high degrees of intelligence – trading coloured tokens for tools with which to break open containers with food inside. They also had two monkeys separated by a glass screen – on one side was a container with nuts inside, but sealed over with a cover. On the other side, a sharp stone that could be used to cut the cover open. The monkey with the tool passed the stone through a small opening in the screen and the other monkey used this to open the container and then reach the nuts. The monkey passed some nuts back through the screen as a sign of gratitude for the act of co-operation.

These same monkeys also showed they can feel injustice too. The first received a biscuit in return for a token; the next monkey received a grape. When the first monkey saw this, it refused the biscuit the second time round, especially when it saw the second monkey get another grape for the exact same token. The first monkey was happy enough to have received the biscuit, however once it saw it’s companion get a far tastier reward it really felt that it was unfair.

Back in Brazil, the monkeys displayed even greater degrees of fore-sight and planning. They manage to have a never ending supply of nuts to eat by first of all tapping the nuts to see how ready they were to open – if not quite ready, they would peel off some of the outer husk, then drop the nuts to the forest floor where they’d ripen faster through their new thinner skin. There would already be some nuts that they’d dropped on a previous occasion ready to eat. They would take these to an anvil rock and by carefully placing the nuts in appropriate hollows in the rock, they’re able to smash them open with rocks. The rocks they use are smooth round rocks from a river several kilometres away – this is an amazing example of their incredible fore-sight – that they were able to imagine that these rocks (which were often very heavy) could be used as nucrackers, and then carry them so far. The anvils appear to have been used for several hundred years by the monkeys.

I always find it fascinating when I see intelligent animal behaviour. I remember seeing the footage of the New Caledonian crow (Corvus moneduloides) who when presented with food at the bottom of a glass tube, would bend a piece of wire into a hook and use this to pull the food out. You can see footage of this here: http://news.bbc.co.uk/1/hi/sci/tech/2178920.stm.

There’s also a fascinating new story where the crows are shown to use one tool to retrieve another tool which is then used to reach food, this is considered to be reasoning skills on a par with that of primates, including humans. You can see footage of this extraordinary feat at the University of Auckland’s website: http://language.psy.auckland.ac.nz/crows/

There’s a story about the monkey’s sense of injustice on the BBC website: http://news.bbc.co.uk/1/hi/sci/tech/3116678.stm

A related link to Sarah F. Brosnan at Emory University here: http://userwww.service.emory.edu/~sbrosna/

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