Crows completed 4 of 6 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 counterintuitive cues for a U-shaped displacement task. According to the authors, results indicate crows may possess a sophisticated—but incomplete—understanding of the causal properties of volume displacement, rivalling that of 5-7 year old children.
Sarah Jelbert added, "These results are striking as they highlight 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."
This video shows example trials for each of the six experiments.
(Photo Credit: Sarah Jelbert)
Crows understand water displacement at the level of a small child.
(Photo Credit: Sarah Jelbert)
Source: PLOS