A quartet of clever rooks have provided evidence that one of Aesop’s fables could have a basis in fact. The tale in question tells the story of a thirsty crow. The bird comes across a pitcher with the water level too low for him to reach. The crow raises the water level by dropping stones into the pitcher. (Moral: Little by little does the trick, or in other retellings, necessity is the mother of invention) [AP]. In the new lab experiment, four rooks each dropped stones into a clear plastic tube, which raised the water level high enough to bring a floating worm within reach.
Rooks and crows are both in the corvid family, which researchers say rivals the great ape family for intelligence and tool use–the only other animal that has performed a comparable task was an orangutan, who spat into a tube to gain a floating peanut. Says study coauthor Nathan Emery: “We have performed a large number of studies on both corvids … and apes, and have found that the crow’s performance is on a par or often superior to apes. However, it is not particularly useful to say that one species is more or less intelligent than another because often the playing fields aren’t even” [The Independent].
Rooks are not known to use tools in the wild, but have proven remarkably adept with them in labs: The same group of four birds previously fashioned hooks out of wires and used them to pull food-bearing buckets up through a glass tube. Emery says the new study “suggests that they can not only think through complex problems requiring the use of tools, but imagine the consequences of their actions without trial-and-error learning, and create novel solutions to these problems that have never been encountered before” [The Independent].
In the experiment, described in Current Biology, the rooks proved highly accurate, placing in only the precise number of stones needed to raise the water level to a reachable height. Instead of trying to get the worm after each stone was dropped, they apparently estimated the number required from the outset and waited until the time was right [LiveScience]. And when given a choice of small and large rocks to use the birds chose to use the bigger stones, suggesting that they knew those rocks would displace more water and bring the tasty worm up faster.
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Video: Christopher Bird