Chris Bird, Department of Zoology, Cambridge
Chris Bird - We’ve been looking into the tool use of rooks. Now, rooks are a member of the corvid family, the crow family, and the crow family has been known to be really intelligent, and probably the most intelligent of the birds. They have a really large brain-to-body size ratio. They are capable of doing some quite remarkable things with objects, using them as tools to solve particular problems.
Meera - So knowing about this intelligence to do with rooks, you’ve been doing some interesting experiments with them to find out just how smart they are?
Chris Bird - Yeah, precisely. We’ve basically been giving them tool use experiments where they have to solve a problem that they’ve never seen before. When we‘re giving them these problems, we’re looking at whether they’re able to solve them using an understanding of how the problem works and an understanding of how the tool works. When we’re looking at their solutions, we’re looking at what they do on the very first trial. So not whether they’re solving it through trial and error but whether they’re solving it through insight into the problem. Basically, what we've found is that they’re capable of showing these insightful solutions to novel problems using tools.
Meera - How have you actually gone about experimenting this?
Chris Bird - We’ve basically given them a variety of tests. In the first set of tests, we gave them an apparatus which had a platform on which a wax worm, their favourite food was suspended and the birds couldn’t reach that. But they could collapse a platform by dropping a stone down the tube and they would select the right size and shape of stone depending on the diameter of the tube. So they were really conscious of the properties of the tool they were using. They also were able to solve that problem by using sticks. So they would use a stick to collapse a platform, they’d also modify the stick to make it able to fit into the tube and they were also capable of meta-tool use which is sequential tool use, using one tool to get another tool. We gave them a second set of experiments where they had a clear Perspex tube about 15 cm tall with a small cardboard bucket in the bottom. In that bucket was a couple of their favourite worms again and we wanted to see whether they were capable of using a hook-like tool to extract the bucket and get at the worms. That’s something which New Caledonian crows have been shown to do in the wild. They’ve been shown to use hook tools and even to manufacture hook tools in order to pull out grubs from holes in the trees. So we gave the rooks these experiments and found that they were just as capable of using a hook tool to extract the bucket. Not only that, but when you gave them a straight piece of wire, they would put the wire into a tube and make their own hook then flip that hook around and use the hook to pull the bucket out of the tube which is really quite remarkable.
Meera - Now, you’ve shown me videos of them doing this and it is actually quite impressive because you can almost see them have this moment’s thought to just think, “Okay, which is the right choice?” And get their worm. Now as well as all of these, you’ve also been doing some experiments to see if one of Aesop’s fables is true.
Chris Bird - Yeah. That’s right. Aesop had his fable called “The Crow and the Pitcher” which is basically about a thirsty crow that couldn’t find anything to drink apart from the small bit of water in the bottom of the pitcher jug and the bird couldn’t reach that water. So, it went off and got some stones and put those into the jug to raise the water level up until it could reach it. Now, we wanted to see whether that was something which was within the possibilities of what the rooks could achieve. There was a report in the early 1980s about rooks in an aviary, using a plug to form a pool of water and they would put in the plug during dry periods so a pool of water formed and they could drink and bathe in it. So, putting that together with the fact that they are capable of using tools, we thought, “Well maybe they’re capable of solving Aesop’s task.” So we gave them a problem that was analogous to Aesop’s fable. We gave them again a clear Perspex tube with a little bit of water in the bottom and a worm floating on the surface of the water, which they couldn’t reach directly. And we gave them a bunch of stones next to the tube and we found that straight away, they would put the stones into the tube and raise the water level up until they could reach the worm.
Meera - Now what I found particularly interesting about this story though was not only did they put the stone in the water to raise the level, but they actually also knew just how many stones they should put in.
Chris Bird - That’s, right. So they would add a number of stones before trying to reach the worm which did suggest that they understood that they needed to raise the water level by a particular amount and they didn’t just try and reach the worm after adding each stone. So, that really showed that they understood how the problem worked and the solution that they were trying to achieve.
Meera - And so, what has it actually taught you overall about their level of intelligence?
Chris Bird - It really emphasizes to us that these birds are remarkably intelligent. They have really high levels of physical intelligence and that their intelligence is really quite general. What I mean by that is that they haven’t just evolved a specific ability for a specific ecological problem. So they haven’t evolved tool use specifically for problems in their environment but their intelligence is general enough and flexible enough for them to be able to transfer what they have learned in other contexts to new contexts like using tools.
Meera - So how does this translate to rooks in the wild?
Chris Bird - So we used captive hand-reared birds because we need to know exactly what their previous experience is. When we’re giving them these problems, we know it’s the first time they’ve seen these problems and when they’re solving them, we know that they’re solving them through insight rather than trial and error learning. When you see corvids using tools in the wild, the New Caledonian crows are the most habitual tool users, they’re using tools because they need to. In New Caledonia, they don’t have access to many types of food, apart from the grubs in holes and trees. So that makes up a lot of their diet. Rooks on the other hand have access to all sorts of other food supplies. They eat lots of seed from agriculture. They eat roadkill, they’re carrion birds like lots of the other corvids and they forage on human rubbish. All of those foods are sort of the easy access foods for them and they don’t actually need to use tools to get to them. So, rooks don’t use tools in the wild not because they can’t, but rather because they don’t need to. And that really emphasizes Aesop’s moral to the thirsty crow which was that necessity is the mother of invention and rooks only really solve the problems using tools when they actually need to.
Meera - Now, one thing this has all being compared to is the intelligence of great apes. So, how are you looking into corvid intelligence alongside ape intelligence?
Chris Bird - Well basically, lots of the experiments that we’ve done with the corvids, researchers have also tried with the great apes, we’re finding that the corvids actually perform much better than the great apes like the chimpanzees. So they’re showing intelligence that rivals those great apes which is remarkable, considering they have such a smaller brain. The size of the brain of the corvid is about the size of a walnut and they don’t have an area of the brain which is typically thought to be the intelligent part of the primate brain called the neocortex. So people for a long time thought, “Well, how can they be doing such intelligent things?” Birds actually have a different part of the brain called the nidopallium which probably evolved from the same area as the neocortex evolved from and the birds are using that area to do a similar thing as the primates use the neocortex for. Now, the two areas have a really different structure. So, it’s interesting to see that convergently, they’ve evolved intelligence using a radically different brain structure.