Cognitive abilities of New Caledonian Crows in relation with tool-use

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Cognitive abilities of New Caledonian Crows in relation with tool-use

Animals in the wild often use objects that can be defined as tools in order to achieve something whether that is foraging, protection, exploration or essentially any action that they wish to do. Tool use has been studied in a number of different animals from primates to insects. A table showing the number of different species investigated in relation to tool use is presented in Bentley-Condit & Smith (2010) highlighting the importance of tool use in an individuals life. Tool use can be defined simply as the use of an external object in order to interact with another object, surface or individual. St Amant & Horton (2008) include in their definition the mediation of the information flow between the interacting bodies whether they are individuals or part of the environment. In this paper a widely studied species, the New Caledonian Crows (Corvus moneduloides) and their tool use and interaction is reviewed and more specifically the cognitive or lack of cognitive mechanisms that enable this sort of manipulation of objects is studied.

The cognitive mechanism responsible for the tool usage in New Caledonian Crows and other animals has not yet been identified even for simple tasks like pulling a string however there are two major hypothesis for the string pulling experiment and tool use in general. The first hypothesis is the insight hypothesis which states that the individual can plan out the whole process of getting to the reward and then put that plan into effect. Ravens were tested in two experiments, one was they got the reward by pulling the string upward and the reward came to them while the other was pulling the string downward to get the reward to move towards them. Almost all of the ravens succeeded in the first experiment but none of them succeeded in the second experiment meaning that the ravens associated that by pulling something it came closer so they executed that plan which resulted in failure (Heinrich & Bugnyar, 2005). The second hypothesis is the feedback loop hypothesis which says that the individual pulls the string sees that it’s moving towards it so it keeps on pulling. In the case of the ravens this was proved to be false since even after they saw that pulling the string down caused the food to get closer they still could not continue that action in order to get the food so by taking that experiment in consideration the insight hypothesis is valid. Another experiment performed with string pulling was having new Caledonian crows pull a string that brought food to them however the apparatus was restricted visually. The experiment showed that the crows did not have any actual insight on the mechanism of the experiment so they just showed the feedback loop hypothesis. The experiment was also reproduced with multiple pieces of string with different colours or patterns, with only one having meat as a reward and the crows showed a failure to understand the relationship of the reward with specific strings (Taylor et al., 2010). This however can mean that different species may have different cognitive abilities in relation to tool making and tool usage or even that maybe different populations of the same species may have different tool use behaviour.

New Caledonian crows have some cognitive ability to understand the tool usage and shape a matching tool to recreate what they know will work. In an experiment by Weir et al. (2002) the crows were presented with two pieces of wire, one bent and one straight. When the hooked wire was removed, Betty a female crow created a hook with the straight wire. These led to a hypothesis and eventually further testing that a new Caledonian crow will bend a straight wire into a new shape in order to achieve its goal. The tool shaping was not the unexpected part since Caledonian crows are known for making hooks from naturally occurring materials (Hunt, 2000). The unexpected part was that the crow used a material that was novel and created something in a way that would not be applicable to materials in the wild. The authors decided to further investigate the hypothesis of novel material tool making by introducing new materials to the crow and it was observed that the crow sometimes tried to get the food with the unbend end of the material leading to the assumption that the crows don’t understand the mechanics of the hook usage just that this shape is the proper one to get the food (Weir & Kacelnik, 2006). These showed that the crow might not have a cognitive ability rivalling humans but it shows that it understands up to a level the potential use of novel objects in tool making and usage.

The use of meta-tools or sequential tool use was also investigated by having the crows extract a tool that was needed to extract another tool in order to get the food reward. An experiment was performed for up to three tools used. Most of the birds managed to get the reward with two sequential tools however with three tools only one individual reached the reward. Another interesting fact in this experiment was that one individual left the tools after failing to extract them and retrieved a natural tool it had in order to successfully get to the reward. Further experiments in some individuals showed that as the crows became more experienced they tended to be more decisive and accurate in their actions. However the authors state that these experiments do not show any complex cognitive mechanisms for tool use since sequential tool use can also occur simply by chaining. The errors performed by the crows during testing indicate that they don’t have an outline of the series of actions that they take but they learn to associate certain tools that are presented with certain tasks like getting food (Wimpenny et al., 2009).

However cognitive abilities will only get you so far since the individual must have physical features that will enable it to interact with tools and use them accordingly. In a study by Troscianko et al. (2012) showed that new Caledonian crows have a visual topography that allows them to use tools properly and also the shape of their beak is ideal for tool handling. This means that the physical properties that the crows’ possess may enable them more tool use than other birds. However since there are only a few bird species that use tools the relationship between physical features and successful tool usage cannot be properly investigated. In a related note it was found that new Caledonian crows had relatively larger brains than other birds which could account for the increased cognitive skills and tool usage of the crows (Cnotka et al., 2008).

Wimpenny et al. (2011) first tested the hypothesis that the crows used tools in contexts outside food retrieving but also used them in order to contact novel objects when they were presented. Further investigation in the matter was done by Taylor et al. (2012). More specifically the authors tested if individuals would prefer to use tools to touch a novel object that they might consider risky instead of their beaks. It was observed that when a fake snake was present in the bait box instead of something else the crows preferred to touch the box with the tool more often. Interestingly it was also observed that when the snake was present the crows failed to get the food in more instances. This could mean that new Caledonian crows have a disabled cognitive ability in the presence of danger maybe not able to process multiple streams information simultaneously resulting in failure of the task.

Further cognitive abilities in new Caledonian crows were observed by watching the behaviour of the crows when a stick movement originated from human interaction and when there was no visual agent to cause the stick to move. By seeing no one moving the stick the crows were far more likely to investigate the reason behind the movement than when they could see someone behind the stick. This showed that crows have cognitive abilities enough to understand why a stick could be moving and to wonder why a stick is moving when there is no apparent reason (Taylor et al., 2012).

Experience has been shown to reinforce a lot of actions in most animals where they learn to associate certain actions with a result showing the plasticity of cognitive behaviour. The actions are not limited to food but include all sorts of behaviour including defence and avoidance so it would be logical to assume that tool use may be reinforced by experience. Von Bayern et al. (2009) tested six crows out of which four had no previous experience with the action they wanted them to perform. The two experienced ones showed no difficulty in performing the task and out of the four naive birds, 2 also succeeded in getting the reward without any previous knowledge to the mechanism of the action. However again the authors observed inconsistencies with the actions of the birds since they performed certain actions that did not show any insight to the model of the mechanism they were expected to do. Notable was the fact that a crow tried to collapse the platform, which could only be collapsed by dropping stones, with one of its feathers. This shows that the crow had no concept that a lot of weight was required to collapse the platform and believed that even a further could do it. The concept of tool understanding was investigated by Taylor et al. (2011) where they performed a series of experiments all revolving around the concept of adding objects to raise the level of the water in order to get the reward. Objects of different sizes, densities, weights so basically objects of different physical properties were presented to the crows and they chose the ones that they believed would have the best impact. This was observed by the birds’ preference to choose objects that were more likely to raise the water level while discarding others sometimes without even testing them in the water first. More tests were performed trying to see if a link between a certain object with the reward was formed however across 20 trials none of the crows showed to make an association between the large stone which indicated success and the reward. The authors comment that this shows that these experiments show that more complex cognitive abilities allow the crows to get the reward since they showed no associative mechanism between objects and reward.

Most of the studies on new Caledonian crows were done with a small number of individuals usually 6-12 crows. Also since crows can live for a number of years a lot of individuals were used in different experiments since they already exhibited an ability to use tools. One could hypothesize from this that only a small number of individuals can actually use tools, however there is experimental evidence of different crows used and since it is endemic to a specific area all the crows could be part of the same ecosystem or even population hence have only minor behavioural differences. The fact that these crows exhibit tool use in the wild also provides reinforcement to the hypothesis that they are highly intelligent and proficient tool users. It is shown that new Caledonian crows have highly cognitive intelligence however the extend of it is yet unknown. The experiments performed mostly show that the crows could be somewhere between the two hypothesis that are presented for the mechanisms of tool use. The inconsistencies in their actions showed the lack of insight however the ability to solve these tasks also showed some planning meaning they may not plan the whole action beforehand however they may plan each step at a time. Further experiments could discover the extend of the crows cognitive abilities but also study more scenarios of how tool use in new Caledonian crows could benefit the fitness or wellbeing of the individual or the population as a whole.


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Yiannis Christodoulides