New Caledonian crows make tools with a sophistication that arguably surpasses any animal besides ourselves. There are signs crows can learn from each other, and their technology may even be advancing, but researchers have been puzzled how such unsociable animals, lacking in language, can do this. A new study shows that even though Corvus moneduloides are relatively solitary creatures, they are capable of learning new tool-making techniques and applying them from memory in a way never before seen in animals besides ourselves and our ancestors.
Although corvids in general are impressively intelligent birds, New Caledonian crows are something special. They bend twigs and tear leaves to make hooked tools to extract grubs in the wild, and have taken to shaping wire with enthusiasm. If this still doesn't impress you much take a look at this video and ask yourself how many humans could solve a sequential challenge so quickly.
Scientists are puzzled how they acquire some of these skills, since they don't appear to imitate each other, even in captivity. Dr Sarah Jelbert of the University of Auckland has proven that when shown a novel tool, and taught its effectiveness, these crows can learn to fashion something similar from memory. She proposes in Scientific Reports crows learn from watching their parents or by finding tools discarded by others, and sometimes make advances on these, leading to a developing technological sophistication.
Jelbert taught eight crows a trick they would definitely not have evolved in the wild. She created a crow vending machine, which rewarded them with food when they inserted pieces of colored paper (portraits of reigning monarchs or notable persons not required).
Once the crows had grasped the paper-for-food idea, Jelbert gave the crows an impractically large piece of colored paper. The crows tore the paper up, four of them without needing a hint, until sections could fit into the machine. The birds were then presented with sheets of two different colors, and only rewarded when they made currency out of one of them. All but one bird quickly learned to only use the right colored paper.
Having thus prepared her subjects, Jelbert applied the true test, offering them two different sized pieces of paper, with only one size bringing a reward. Once the birds learned to only use the desired sized paper, Jelbert gave them a large piece of cardboard. The birds eagerly set about tearing up the card and inserting it, making pieces close to the size they had previously been taught to use.
One crow, named Emma, went to particular lengths to get the sizes right, tearing pieces twice until they were very similar in size to the ones she had been taught to use – even though she did not have an appropriately sized template with which to compare her work.
This feat may not seem as impressive as the sequential thinking displayed in the first video, but it's worth thinking about the process required to get there. The crow needs to recognize there is something special about a particular size of paper, remember that size accurately, and be willing to invest the effort to tear the paper up appropriately without having opposable thumbs. Emma even showed an unnecessary level of perfectionism.
Jelbert's work explains regional variations seen in tool manufacturing across New Caledonia. These appear culturally transmitted, and there is evidence these are evolving. Jelbert and her colleagues describe the behavior as “mental template matching”, something we have never seen before among non-humans.
We still don't know, however, why the birds of two smallish Pacific Islands can do things only humans can elsewhere.