NEW RESEARCH HAS revealed that crows can understand water displacement.

According to researchers in New Zealand, the birds have a causal understanding – at the level of five to seven year olds – of how to displace water to receive a reward.

Understanding causal relationships between actions is a key feature of human cognition. To try and understand the extent to which animals are capable of something similar, scientists from the University of Auckland used the Aesop’s fable riddle.

In that story, subjects drop stones into water to raise the level and obtain a once out-of-reach reward. In the project, New Caledonian crows- who are already known for their intelligence and innovation – were tested using this method.

We already know that New Caledonian crows make tools, such as prodding sticks and hooks, the only non-primate species able to do so.

Credit: Sarah Jelbert; CC-BY

Publishing her results in the PLOS ONE journal, lead researcher Sarah Jelbert said her project highlights both the “strengths and limits of the crows’ understanding”.

“In particular, the crows all failed a task which violated normal causal rules, but they could pass the other tasks, which suggests they were using some level of causal understanding when they were successful.”

During six experiments, six wild crows were tested after a short training period.

The authors of the study noted “rapid learning” over the course of the tasks – although not every bird finished each job.

The researchers explained that the tasks did not test insightful problem solving, but were directed at the birds’ understanding of volume displacement.

The crows completed four of six water displacement tasks, including:

• Preferentially dropping stones into a water-filled tube instead of a sand-filled tube;
• Dropping sinking objects rather than floating objects;
• Using solid objects rather than hollow objects;
• And dropping objects into a tube with a high water level rather than a low one.

However, they failed two more challenging tasks – one that required understanding of the width of the tube, and one that required understanding of counter-intuitive cues for a U-shaped displacement task.

Jelbert concluded that crows may possess a sophisticated – but incomplete – understanding of the causal properties of volume displacement, rivalling that of 5-7 year old children.

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