Crows proved to perform as well as seven to 10-year-olds on a "cause and effect" water displacement test.
The research was conducted by UC Santa Barbara's Corina Logan and colleagues. It was published today in the journal Plos One.
"We showed that crows can discriminate between different volumes of water and that they can pass a modified test that so far only [seven]-to 10-year-old children have been able to complete successfully. We provide the strongest evidence so far that the birds attend to cause-and-effect relationships by choosing options that displace more water." Logan said.
The research team caught the crows in the wild and kept them in aviaries for about five days. Getting particular test subjects to do what the researchers wanted proved to be difficult.
"So I thought, let's pretend the sky's the limit and I can train them to do whatever I want," Logan said. "I started by pointing at the one I wanted and continuing to point until he or she flew out. I got to the point where I could stand outside the aviary and point at the one I wanted and it would fly out while the other birds stayed put."
The testing room contained two beakers of water; both were the same height but one was wider than the other. The purpose of the test was to determine if the birds could distinguish between the two different water volumes. The team wanted to know if the birds would understand dropping a stone in the more narrow beaker would raise the water level higher than the wider one.
"When we gave them only four objects, they could succeed only in one tube -- the narrower one, because the water level would never get high enough in the wider tube; they were dropping all or most of the objects into the functional tube and getting the food reward," Logan explained. "It wasn't just that they preferred this tube, they appeared to know it was more functional."
The team also tested the crows with as U-tube experiment in which dropping a stone in a certain beaker would raise the water level in another containing a food reward. Another set of the color-coded tubes did not have this feature. The crows proved to be able to determine the correct tube to drop the stone in; a task that is too difficult for children between the ages of four and six.
