We also examined neophobia by measuring the number of startle responses rapid movement away from the box while flapping the wings and retreat responses rapid movement away from the box without wing flapping.
Mean number of neophobic responses across the first three trials. When the crows picked up a tool, they extracted food with it Responses to the snake were not affected by age or sex. The low number of tool-mediated extractions prevented statistical testing of the effect of sex and age on variation in this behaviour.
Our results show that New Caledonian crows are capable of context-specific tool use. The crows picked up tools and used them to make contact with a baited box and its contents more often when a novel snake model was inside than when a novel teddy bear or a familiar food bowl was inside. This difference in response means that we can rule out an association between novel objects and tool use, or the coincidental holding of a tool while investigating novel objects, as explanations for the crows' behaviour.
Furthermore, our results show that the greater frequency of tool use with the snake was not because the crows preferred to manipulate objects more when stressed owing to object novelty, as their neophobic responses to the teddy bear and the snake were not statistically different.
That crows showed similar levels of neophobia to both the snake and the teddy bear, but used tools more in the snake condition, suggests that this species' neophobic reactions do not mirror their evaluation of risk. This may be because crows are scared when objects are a potential threat and when they are new. The evaluation of the snake as a greater threat did not generate differential neophobic responses to the snake and the teddy bear probably because the latter provoked heightened neophobia owing to its novelty.
That neophobia increased the crows' time near a potential predator could be seen as maladaptive. Although pre-testing showed that all crows were competent tool users, they were poor at extracting food in the presence of the snake and teddy bear.
Whether this was due to the crows using the tools to gather information about the snake and the teddy bear [ 7 , 13 ], or tool use being disrupted by neophobia, is unclear. Tool choice, however, was not affected by the stimuli in the box because the crows' preference for longer tools was not dependent on condition. The context-specific tool use shown by New Caledonian crows in our study suggests that this species maintains differently structured representations of body and tool in terms of the value assigned to them.
That is, these birds value their body more than a tool and so in risky situations perform context-specific tool use. However, our results do not indicate how these representations differ structurally. The crows may understand the conceptual difference between a tool and their body. Alternatively, this information may be represented at lower cognitive levels, such as through the use of heuristics.
Similarly, our findings do not indicate how the representations of body and tool develop and particularly whether past experience with potential predators is needed. Nevertheless, the performance of the crows suggests that this species maintains differently structured representations of body and tool during active tool use, as primates do. Determining how New Caledonian crows form tool representations, and whether they have the same structure as those of primates, will be a focus of future work.
Wardrobert and his family for access to their land. We also thank Mick Sibley for catching the crows and the referees for their many helpful comments, in particular the alternative suggestions proposed for the variation in neophobia and the formation of tool representations.
This work was supported by the Cogito Foundation and a J. National Center for Biotechnology Information , U. Journal List Biol Lett v. Biol Lett. Published online Sep 7.
Alex H. Hunt , 1 and Russell D. Gray 1. Gavin R. Russell D. Author information Article notes Copyright and License information Disclaimer. Received Aug 4; Accepted Aug This article has been cited by other articles in PMC. Abstract Humans and chimpanzees both exhibit context-dependent tool use. Keywords: context-dependent tool use, New Caledonian crow, neophobia response.
Introduction The Mahabharata, the Sanskrit epic of ancient India, tells the story of the sage Chayvana [ 1 ]. The crows first had to pull up a string to get a short stick, then use that short stick to remove a long stick from a toolbox and finally used the long stick to reach the food.
Amazingly, they worked out how to do this successfully. Further experiments carried out at Oxford suggests that crows can also use sticks as tools to inspect all sorts of objects, possibly to assess whether or not they present a danger. The idea for the experiment came from observing the birds using tools to picket random objects, such as a picture of a spider that was printed on some cloth. As a further precaution, all the crows had been fed beforehand on eight occasions.
Barney began by using a stick for inspection. One involved a rubber snake. He then prodded it with the stick. In other experiments two different birds called Pierre and Corbeau also made a first approach with tools. On three separate occasions, Pierre used a short piece of wood chip to touch a light which was flashing, and Corbeau was seen prodding a metal toad with a stick significantly the crows tender to use sticks only to make their first contact with the object.
Subsequently, they either ignored the object or dropped the tool and pecked at the object, which is very different from using the tool to get access to food. So what conclusions can be drawn from the research? 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.
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. 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.
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. More on New Caledonian crows : I highly recommend the excellent website of an Oxford group who are studying these birds. Have a look at this article about rooks for an example. Spontaneous metatool use by New Caledonian crows. Curr Biol All rights reserved. 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.
Share Tweet Email. Go Further.
0コメント