The ability to use tools has been suggested to indicate advanced physical cognition in animals. Here we show that rooks, a member of the corvid family that do not appear to use tools in the wild are capable of insightful problem solving related to sophisticated tool use, including spontaneously modifying and using a variety of tools, shaping hooks out of wire, and using a series of tools in a sequence to gain a reward. It is remarkable that a species that does not use tools in the wild appears to possess an understanding of tools rivaling habitual tool users such as New Caledonian crows and chimpanzees. Our findings suggest that the ability to represent tools may be a domain-general cognitive capacity rather than an adaptive specialization and questions the relationship between physical intelligence and wild tool use.cognition ͉ intelligence ͉ Corvus ͉ frugilegus ͉ hook

Recent research with Rooks has demonstrated impressive tool-using abilities in captivity despite this species' classification as a non-tool-user in the wild. Here, we explored whether another non-tool-using corvid, the Eurasian Jay, would be capable of similar feats and investigated the relative contributions of causal knowledge and instrumental conditioning to the birds' performance on the tasks. Five jays were tested on a variety of tasks involving water displacement. Two birds reliably interacted with the apparatuses. In these tasks, both birds showed a preference for inserting stones into a tube containing liquid over a tube containing a solid or a baited 'empty' tube and also for inserting sinkable items over non-sinkable items into a tube of water. To investigate the contribution of instrumental conditioning, subjects were then tested on a series of tasks in which different cues were made available. It was found that, in the absence of any apparent causal cues, these birds showed a clear preference for the rewarded tube when the food incrementally approached with every stone insertion, but not when it simply "appeared" after the correct number of stone insertions. However, it was found that subjects did not prefer to insert stones into a tube rewarded by the incremental approach of food if the available causal cues violated the expectations created by existing causal knowledge (i.e. were counter-intuitive). An analysis of the proportion of correct and incorrect stone insertions made in each trial across tasks offering different types of information revealed that subjects were substantially more successful in experiments in which causal cues were available, but that rate of learning was comparable in all experiments. We suggest that these results indicate that Eurasian jays use the incremental approach of the food reward as a conditioned reinforcer allowing them to solve tasks involving raising the water level and that this learning is facilitated by the presence of causal cues.

In Aesop's fable "The Crow and the Pitcher," a thirsty crow uses stones to raise the level of water in a pitcher and quench its thirst. A number of corvids have been found to use tools in the wild, and New Caledonian crows appear to understand the functional properties of tools and solve complex physical problems via causal and analogical reasoning. The rook, another member of the corvid family that does not appear to use tools in the wild, also appears able to solve non-tool-related problems via similar reasoning. Here, we present evidence that captive rooks are also able to solve a complex problem by using tools. We presented four captive rooks with a problem analogous to Aesop's fable: raising the level of water so that a floating worm moved into reach. All four subjects solved the problem with an appreciation of precisely how many stones were needed. Three subjects also rapidly learned to use large stones over small ones, and that sawdust cannot be manipulated in the same manner as water. This behavior demonstrates a flexible ability to use tools, a finding with implications for the evolution of tool use and cognition in animals.

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Some corvids have demonstrated cognitive abilities that rival or exceed those of the great apes; for example, tool use in New Caledonian crows, and social cognition, episodic-like memory and future planning in Western scrub-jays. Rooks appear to be able to solve novel tasks through causal reasoning rather than simple trial-and-error learning. Animals with certain expectations about how objects interact would be able to narrow the field of candidate causes substantially, because some causes are simply ‘impossible’. Here we present evidence that rooks hold such expectations and appear to possess perceptual understanding of support relations similar to that demonstrated by human babies, which is more comprehensive than that of chimpanzees.