Crows understand water displacement
March 27, 2014

Crows Understand Water Displacement Proving Aesop’s Fable

Brett Smith for - Your Universe Online

In a well-known Aesop’s fable, a crow comes across a pitcher with a small, out-of-reach amount of water in the bottom. To get a drink, the crow drops stones in the pitcher until the water level rises enough for the bird to reach it with its beak.

While the point to the fable may be to teach the virtue of ingenuity, a team of scientists from New Zealand and the United Kingdom wanted to see if New Caledonian crows understood the idea behind displacing water with objects to receive a reward.

While previous research has shown that these crows are capable of solving this problem, the study team said they wanted to see if New Caledonian crows could demonstrate an ability to understand the concept of volume displacement – such as the fact that solid objects displace more water when they sink in water than hollow objects.

After a brief training period, the crows were tested in six different tasks that each had different tweaks to see if the birds did in fact understand the concept of volume displacement. The crows were able to complete 4 of 6 tasks, such as dropping stones into a water tube to reach a prize instead of dropping stones into a sand-filled tube. Other successful tests included dropping sinking objects rather than floating objects, choosing solid objects over hollow objects, and dropping objects into a tube with a high water level as opposed to a low one.

In one of the tasks, the crows failed to understand the significant of the width of the tube. The crows also had trouble with a U-shaped tube, which offered counterintuitive cues.

[ Watch the Video: New Caledonian Crows Understand Reward ]

The study team said New Caledonian crows probably possess an incomplete understanding of volume displacement, similar to that of 5-7 year old children. A report on their research was published in the open-access journal PLOS ONE.

"These results are striking as they highlight both the strengths and limits of the crows' understanding,” said study author Sarah Jelbert, a researcher from the University of Auckland. “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."

Previous research from some of the same scientists revealed that New Caledonian crows are capable of using multiple tools to solve problems.

In the researchers’ report, published in Proceedings of the Royal Society B, they described how they gave the crows a three-stage, multi-tool problem to solve.

“The task involved three distinct stages: (i) obtaining a short stick by pulling up a string, (ii) using the short stick as a metatool to extract a long stick from a toolbox, and finally (iii) using the long stick to extract food from a hole,” they wrote. “Crows with previous experience of the behaviors in stages 1-3 linked them into a novel sequence to solve the problem on the first trial. Crows with experience of only using string and tools to access food also successfully solved the problem.”

The researchers added that their finding suggests “high innovation rates (seen) in the wild may reflect complex cognitive abilities that supplement basic learning mechanisms.”