Clever New Caledonian crows use one tool to acquire another

You don't have to be particularly intelligent to use tools - many animals do so, including some insects. But it takes a uniquely intelligent animal to be able to combine different tools to solve a problem. We can do it, the great apes can do it, and now the New Caledonian crow joins our exclusive club.

Animals can use tools using little more than pre-programmed behaviour patterns that require little intelligence. But combining tools, or using one tool on another (a metatool, if you will), is a different matter entirely - that takes reasoning. This type of intelligence has been the engine of human innovation. It allowed us to use simple tools to make advanced ones, or to combine different tools into increasingly complex machines.

The majority of animals lack the ability to manipulate tools in this way and in primates, the line is drawn at the great apes - they can (mostly) do it, but monkeys struggle. So it may come as a surprise that a humble bird has now been found to use metatools to the same standard as our ape cousins - the New Caledonian crow.

Of course, anyone familiar with the exploits of the New Caledonian crow probably won't be surprised at all. These are no bird-brains; they are, in fact, strong contenders for the title of the most intelligent bird, and expert tool-makers to boot. Their ingenuity is most apparent when they are searching for food, converting twigs and branches into hooks and spears for dislodging juicy grubs from hollows in wood.

But while many birds do this, the crows are special. They can spontaneously make new tools from materials they have never seen before, like a hook from a bent wire. They have also been seen manufacturing new tools by altering existing ones and passing their newfound technology onto others, a ability even great apes aren't known to have. Now, Alex Taylor and colleagues from the University of Auckland have found that they can use one tool on another in the quest for food.

They showed seven crows a morsel of meat in a hole, and a stick that was too short to reach it. The birds also had access to two cages, one containing a useless stone, and the other containing a long stick that could reach the meat but was itself out of reach.

To a bird, every single crow worked out how to get the meat - they used the short stick to lever the long one out of its cage, and used that to retrieve the food. Their performance is all the more impressive because it equals that of gorillas and orang-utans, slightly surpasses that of chimps and goes well beyond the abilities of monkeys.

It was clear to Taylor that the crows weren't relying on pre-learned behaviours. He had never seen a similar technique used in the wild during three years of studying these birds. Nor were they using trial-and-error for three of them - Icarus, Luigi and Gypsy - worked it out on their first go. You can actually see videos of Gypsy's and Icarus's first trials in MPG format.

In a second test, the team reversed the position of the sticks, so that the long one was initially available and the short one was inside the cage. The crows used the long stick to probe the cage with the short one, but quickly abandoned their efforts, ignored the short stick and used the longer one to extract the meat.

Taylor believes that these experiments show that the crows used 'analogical reasoning', which requires them to use experience from one problem to solve another. They need to go beyond thinking "this tool will help me reach that food" to "this tool can be used to access out-of-reach objects". It's a subtle conceptual leap, but one that only a few species can make.

Humans probably went through a similar sequence of mental leaps during our evolution. At first, we used tools to get at food, by thrusting rocks at nuts to crack their shells for example. Soon, we realised that the same actions could be used to fashion blades, objects which weren't themselves edible but which would be very useful in getting even more food.

More on New Caledonian crows: I highly recommend the excellent website of an Oxford group who are studying these birds. Since this post was originally written in 2007, there's been a flurry of great research on intelligent crows and their relatives. Have a look at this article about rooks for an example.

Reference: Taylor, Hunt, Holzhaider & Gray. 2007. Spontaneous metatool use by New Caledonian crows. Curr Biol 17: 1-4.

More on bird-brains:

• City mockingbirds can tell the difference between individual people
• Sparrows solve problems more quickly in larger groups
• Bird-brained jays can plan for the future