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Crows Understand Water Displacement and Show Causal Understanding of a Small Child

Crows understand water displacement at the level of a small child. Credit: Sarah Jelbert; CC-BY

Crows understand water displacement at the level of a small child.
Credit: Sarah Jelbert; CC-BY.

On March 26, 2014, there was an article published in the open access journal PLOS ONE. In the article, Sarah Jelbert and her colleagues from University of Auckland released their research results about the causal understanding of New Caledonian crows. Such birds might understand how to get a reward by displacing water and their causal understanding level could be similar to that of a 5-7 year-old child.

As we know, one of the important characters of human cognition is to understand causal relationships between actions. But how well non-human animals could understand causal relationships is yet to be found. Therefore, scientists resort to the Aesop’s fable riddle in order that they could identify causal understanding of water displacement of New Caledonian crows. According to the Aesop’s fable riddle, the subjects would put stones into water so as to make the water level higher and help them collect an out-of reach-reward. It is well-known that these crows are intelligent and innovative, because they are regarded as the only non-primate species that are capable of making tools, like hooks and prodding sticks. After being trained for a short period, six wild crows were given the respective test. During the six experiments, the authors noted the rapid learning of such crows (although not all the crows finished their experiment completely). The authors make it clear that these tasks were focused on the birds’ understanding of volume displacement rather than testing their ability of insightful problem solving.

As for the six experiments, New Caledonian Crows had completed four water displacement tasks. They were able to preferentially put stones into a tube full of water rather than a tube full of sand, dropping sinking objects instead of floating objects, picking up solid objects to ignore hollow objects, and throwing objects into a high-water-level tube instead of a low one. Unluckily, such crows were incapable to accomplish two more challenging and difficult tasks, one involved in identifying the width of the tube, and the other related to knowing the counterintuitive cues to finish a U-shaped displacement task. According to the experiment results released by the authors, such crows might have the ability to understand the causal properties of volume displacement through a sophisticated, but incomplete approach , which could compete with that of a 5-7 year old child.

With all the data collected from the experiments, Sarah Jelbert summarized: The final results from experiments did surprisingly demonstrate both the strong and weak points of the crows’ understanding. If the crows were given a task violating the normal causal rules, they would definitely fail. However, in the face of the tasks that require some level of causal understanding, they would complete them successfully.


  1. Sarah A. Jelbert, Alex H. Taylor, Lucy G. Cheke, Nicola S. Clayton, Russell D. Gray.Using the Aesop’s Fable Paradigm to Investigate Causal Understanding of Water Displacement by New Caledonian CrowsPLoS ONE, 2014; 9 (3): e92895 DOI: 10.1371/journal.pone.0092895