New Caledonian crows (Corvus moneduloides) make and use tools, and tool types vary over geographic landscapes. How the birds transmit knowledge to each other is the focus of a new study published last month in the journal Learning & Behavior.
A New Caledonian crow (Corvus moneduloides) uses a twig. Image credit: Jolyon Troscianko.
“We don’t know whether New Caledonian crows have cumulative technological culture, and one of the reasons is that we don’t know how they learn,” said Corina Logan from the the University of Cambridge, UK, and the University of California Santa Barbara, who is the lead author on the study.
“There’s a hypothesis that says in order for cumulative technological culture to occur you need to copy the actions of another individual. And we don’t know whether the crows are paying attention to the actions of others when they learn from someone else.”
But the crows have been observed using tools they’ve made out of long, narrow, palm-like Pandanus leaves.
“It has a serrated edge, and they cut into one side of the leaf, then make another cut farther down and then rip off the part in between. It makes a tool they can use to dig grubs out of logs,” Logan said.
Even more curious, the crows have been observed using tools made of the same material but in different shapes – wide, narrow and stepped, which might be more structurally sound.
However, no one has been able to explain the geographic variation in tool shapes – all three shapes are seen at the south end of New Caledonia, while the stepped tool is more prevalent everywhere else.
“It’s thought that in order for tool shapes to be transmitted, one bird would have to watch another cutting the leaf and then mimic that bird’s actions. That would require imitation or emulation,” Logan said.
Logan and her colleagues from New Zealand and UK devised a study to look at all the learning mechanisms – social and asocial – New Caledonian crows employ when solving a foraging problem. To level the playing field so that those birds with more experience with one particular tool don’t have an advantage over the others, the team gave them a novel non-tool task.
The team designed the experiment based on apparatus used by UK scientists in a similar study they conducted on meerkats.
“I used two apparatuses with multiple access points on each, so we could look at whether the crows were imitating or emulating, whether they were just paying attention to another crow’s general location or whether they were paying attention to a specific area on an apparatus that another crow was interacting with,” Logan said.
The team found that the crows don’t imitate or copy actions at all.
“So there goes that theory. Assuming how they learn in a non-tool context carries over to a tool context, they wouldn’t copy the actions of individuals they see cutting up Pandanus leaves to make tools,” Logan said.
But the researchers did strong evidence of social learning: if one crow sees a companion interacting with a particular area of the apparatus, reaching its bill through a door and pulling out a piece of boiled egg – the treat – the former is far more likely to try that particular door on either apparatus before choosing the other access options.
“It’s called stimulus enhancement. That’s the social learning mechanism they’re using. But there’s another interesting aspect: Once they see another bird interact with the door, they go to that door and then begin to solve the problem on their own. And now they completely ignore social information and they just use trial and error learning to open the door and extract the food,” Logan explained.
Even if one crow is at an apparatus and tries unsuccessfully to open the door, if he or she sees another crow on the second apparatus actually solving the problem correctly, the first crow doesn’t use that information.
“The social learning attracts them to a particular object and then they solve it through trial and error learning after that,” Logan said.
“So we thought, ‘Okay, if they don’t imitate or emulate, how could they still have cumulative technological culture?’ Perhaps it’s a combination of social learning and trial and error.”
Similar to the stimulus enhancement the scientists identified initially, the crow parents could draw their children’s attention to the tools to make them more likely to interact with the tools. In addition, wild juveniles appear to learn how to use the tool through trial and error over the course of several months.
For this study, the team placed the crows in small groups. One was a family that consisted of two parents and their two sons; another included two mated pairs that weren’t related; and the third was made up of an adult and five juveniles. One of the juveniles was likely the adult’s daughter but the rest were unrelated.
It had been previously hypothesized that juveniles do most of the learning, with adults picking up very little, if anything, from the youngsters or from each other.
“It turns out this was mistaken. It didn’t matter what group it was. Everyone learned from everyone – juveniles from juveniles, adults from adults, juveniles from adults, adults from juveniles. It seems that if they have the opportunity, they’ll learn from anyone. But because they live in family groups, it seems to constrain who they have the opportunity to learn from in the wild,” Logan said.
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Corina J. Logan et al. How New Caledonian crows solve novel foraging problems and what it means for cumulative culture. Learning & Behavior, published online August 15, 2015; doi: 10.3758/s13420-015-0194-x
