Among 6 basic water displacement tasks, crows completed 4, including preferentially dropping stones into a water-filled tube instead of a sand-filled tube, choosing sinking objects to floating ones, 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. 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."