Tool Use in New Caledonian crows
One species of bird in particular possesses an extraordinary ability to use tools - the New Caledonian crow (Corvus moneduloides).
New Caledonian crows, which are found on the Pacific island of New Caledonia, make the most complex tools of any animal yet studied apart from humans. For example, they will evolve and improve the shape of their tools over time, and will create left handed or right handed tools. These tools are usually made to help catch insects and other invertebrates.
Russell Gray and his colleagues from the department of psychology at the University of Auckland in New Zealand have studied this species extensively, and were the first to discover that the birds were crafting tools in the wild . In fact they are the only birds known to craft and use tools in the wild.
The discovery that they whittle branches into hooks and tear leaves into barbed probes to extract food from hard-to-reach nooks astounded scientists, who had previously thought that the ability to make tools was unique to primates. Professor Gray said: "They do some really complex looking things. We have seen that they take a whole branch, chop off the side branches and hone away at the end to create a hook, which they use to get grubs."
Other wild crows also use tools. Crows in urban Japan have innovated a technique to crack hard-shelled nuts by dropping them onto cross walks and letting them be run over and cracked by cars. The have even learnt to drop the nuts under cars on pedestrian crossings so that when the traffic stops they can collect their cracked nuts in safety.
Further research in the laboratory and the field has revealed that New Caledonian crows are also innovative problem solvers, often rivalling primates. Experiments have shown that the birds can craft new tools out of unfamiliar materials, as well as use a number of tools in succession.
To further understand how the birds perform these tasks, the University of Auckland team set seven wild crows, which had temporarily been captured and placed in an aviary, a complicated problem. The birds were presented with some out-of reach food; a long tool, which could be used to extract the food, but which was also out of reach, tucked behind the bars of a box; and a short tool, which could be used to extract the long tool, but which was attached to the end of a dangling piece of string tied to the crow's perch.
Professor Russell Gray, from the University of Auckland, explained: "The crows needed to understand they needed the short tool on the piece of string to get the long tool, and then use the long tool to get the food."
The seven birds were split into two groups. The first group of birds were given the chance to try out every individual step in the set-up, before they were presented with the complete multi-stage task. Professor Gray said: "All these birds had to do was to put together things they could already do in the right sequence." Each of the three birds managed to solve the three-stage problem on their first attempt.
A second group of birds was presented with a less familiar situation. While they had previously been shown tasks where food was directly attached to string, and sticks could be used to grab out of reach food, they had never been given a situation where a tool was linked to the string or where one tool was needed to collect a second tool. However, when presented with the multi-stage task, these birds also managed to reach their treat. One bird, Sam, spent 110 seconds inspecting the apparatus before completing each of the steps without any mistakes. Another bird, Casper, also completed on his first try, although he was initially puzzled by the string. The other two birds solved the problem on their third and fourth attempts.
Alex Taylor, the lead author of the research, said: "Finding that the crows could solve the problem even when they had to innovate two behaviours was incredibly surprising." The researchers say that the experiments are helping to shed light on how the crows are carrying out these complicated tasks. Dr Taylor said that while using or creating a single tool could be underpinned by simple learning processes, solving a set of linked problems, suggested that the basis for their innovation is much more complex.
One New Caledonian crow in particular seemed to possess a remarkable ability when it came to solving problems using tools - Betty. Alex Kacelnik, who leads the behavioural ecology group at the UK’s Oxford University, said: "Betty was captured as a juvenile from the field, and she must have been one-and-a-half years old when she came to us. And we didn't have any reason to suspect that she was an unusual animal." However the team discovered, by chance, that Betty was able to perform some remarkable feats that had never been seen before in any other animals.
The researchers were testing how New Caledonian crows selected tools by presenting them with a small bucket filled with some food, which was placed in a well, and pieces of wire, some straight and some with a hook at the end. The aim was to see whether the crows would select the bent wire to retrieve the treat-laden bucket.
But Betty astonished researchers when she selected a straight piece of wire and then used her beak to bend it into a hook so she could pull up the bucket of food. When she was later tested with just the straight wire, Betty repeatedly bent it into hooks - and other experiments with aluminium strips revealed how she would bend, shorten and lengthen the material to get to her food. This was the first time that any animal had been seen to make a new tool for a specific task, without an extended period of trial-and-error learning.
As scientists discover ever-more intelligent behaviour in corvids, they are now trying to understand why this group has developed these special abilities. And New Caledonian crows' tool-use is a key focus.
Professor Gray explains: "What has led to just this one species in this one little island in the Pacific being able to make these complex tools? It's an ongoing mystery." Professor Kacelnik agrees: "This really is the million dollar question. We know that this is heritable - we have demonstrated that if you raise New Caledonian crows, without exposure to any social input, they still would want to use tools to solve problems."
Researchers are also looking at the cognitive processes that underpin this behaviour. Mr Bird says: "The interesting thing is that they can do so many of these clever things that primates can do - sometimes they can do them even better. But their brain is completely different from the mammalian brain. They don't have the area of the mammalian brain that is thought to be the area of intelligent cognition - the neocortex. Interestingly, they have another area, the nidopallium, that might do the same job."
Corvid intelligence research is still in its early days. Christian Rutz, who also works for Oxford's behavioural ecology group, says: "People tend to think corvid cognition research is now incredibly advanced and we've answered most of the questions - I don't think so, I think it is at the very beginning."
To investigate how New Caledonian crows acquire such an amazing ability to make and use tools, Jenny Holzhaider and colleagues at the University of Auckland studied their social organisation in their natural habitat on the island of Maré in New Caledonia .
Young New Caledonian crows learn to use tools by going to "tool-school", where they can observe their parents at work. Unlike many other crow species, New Caledonian crows are not highly social. Instead, they tend to live in small, tight-knit family units comprising two parents and offspring from up to two consecutive breeding years. The parents stay together all year and seem to especially tolerate the presence of the juveniles. Living in unusually small family groups allows parent birds to take juveniles to tool-using sites, and let young birds play with "grown up" tools. "Their social system is based on high quality relationships with a small number of crows, especially immediate family." said co-researcher Gavin Hunt.
The discovery rules out the idea that New Caledonian crows live in complex social groups, and learn their skills from their peers. Instead it suggests that the crows develop their tool-using abilities by "keeping it in the family", say the researchers.
What is more, the parent crows appear to go to considerable lengths to ensure their offspring can learn how to fashion and use tools. "[Juveniles] closely follow and watch their parents' behaviour, are taken to tool using sites, and are 'allowed' to use the tools of their parents," says Dr Hunt. Structuring their education in this way may also help explain how the crows improve their tools over time, as young crows may learn from their parent's mistakes.
- Hunt G. R and Gray R. D 2004 The crafting of hook tools by wild New Caledonian crows. Proceedings of the Royal Society B, vol. 271 no. Suppl 3 S88-S90.
- Holzhaider J. C, Sibley M. D, Taylor A. H, Singh P. J, Gray R. D and Hunt G. R 2011 The social structure of New Caledonian crows. Animal Behaviour, Volume 81, Issue 1, 83-92