Sarah A. Jelbert, a psychologist at the University of Auckland, in New Zealand, led the research -- which presented several crows with a variety of puzzles inspired by Aesop's fables.
In one of Aesop's fables, a thirsty crow is described dropping pebbles into a half-full pitcher of water to raise the water level high enough to score a drink.
When offered similar predicaments -- a pile of stones placed next to a test tube of water containing a floating treat, such as a worm -- the crows we able to show a basic understanding of volume displacement. In most scenarios the tested crow was able to use strewn objects to raise the water level high enough to grab the treat.
The details of their study were recently laid out in online journal PLOS One.
The crows did fail a few of the puzzle variations -- ones that required advanced reasoning, like understanding the varying widths of the tubes and other counterintuitive cues.
"These results are striking as they highlight both the strengths and limits of the crows' understanding," Jelbert said. "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."