Crows Better at Tool Building Than Chimps, Study Says
for National Geographic News
|April 23, 2003|
Although there are many industrious tool-users in the natural world, the only animals with enough brainpower to develop and improve the tools they make have long been thought to be humans. Adding innovative new features, such as a wheel or an engine, to previous designs, was one of those traits some scientists believed made us unique.
Now, according to researchers in New Zealand, a crafty species of crow found on the remote Pacific islands of New Caledonia may prove that this trait isn't so uniquely human after all.
As the scientists detail in the journal Proceedings of the Royal Society B, New Caledonian crows (Corvus moneduloides) have been able to add useful new features to the insect-snagging tools they fashion from leathery pieces of torn leaf. What's more, they say, these innovations are faithfully passed on between individuals and across generations.
"The ability to cumulatively improve tools is one of the features that define humanness. In fact this ability has been crucial for our technological progress," said co-author Gavin R. Hunt, at the University of Auckland in New Zealand. "Our findings therefore remove an important technological difference between humans and other animals," he said.
Chimps Trial and Error
Even in the chimpanzee, tool manufacture is often a haphazard process, cites the study, and chimp tools show little evidence of incremental change over time.
Despite the fact that chimps use tools for a wider variety of tasks, such as foraging and grooming, they don't appear to pass on tool-building knowledge in the same way that people, and possibly New Caledonian crows, do.
Chimps don't share precise details about the manufacture of tools, rather they attempt to come to the same end pointa branch stripped of bark and leaves perhapsthrough a trial-and-error process, said Hunt. Design innovations caught upon by individuals are therefore often not transmitted to the next generation, he added.
In contrast, these crows exactly mimic manufacture techniques learned from other birds, and therefore are able to make use of rare innovative new designs.
Researchers have been aware of the surprising cognitive abilities of these crows for some years now. A captive New Caledonian crow, called Betty, was made famous last year when scientists at Oxford University in England, filmed her making hooks from straight pieces of wire to obtain out-of-reach food.
Snip and Tear
In 2000 Hunt, and his University of Auckland co-worker Russell D. Gray, completed a detailed survey of crow tool-making behavior. The pair were searching for evidence that might prove the possibility of incremental change in crow tools.
In order to test the birds' abilities, the researchers examined manufacture techniques in forests across New Caledonia. Situated in the Pacific Ocean east of Australia, the French islands of New Caledonia contain a unique and isolated group of species.
In addition to twigs, the crows manufacture tools from long and barbed leaves of the pandanus (or screw pine) tree.
Crows snip into the leaf edges and then tear out neat strips of vegetation with which they can probe insect-harboring crevices. These tools have been observed to come in three types: narrow strips, wide strips and multi-stepped stripswhich are wide at one end and, via a manufacturing process that involves stepwise snips and tears, become narrow at the opposite end.
Instead of attempting to locate crows using pandanus leaf toolswhich would have been a logistical challengeHunt and Gray scoured the forests for so-called leaf "counterparts." A counterpart is the exact mirror-image outline, or carbon copy, of the tool's shape left behind in pandanus leaves still attached to the tree.
By examining more than 5,500 tool imprints in 21 sites throughout New Caledonia, the pair were able to assess patterns in the tool design and location and abundance of each tool type. The results suggested that both narrow and stepped tools are more advanced versions of the wide tool type.
No Similar Example
Tool invention is very rare, said Hunt. Therefore it's quite unlikely that each type of leaf tool has been the result of a unique discovery. In addition, the geographical distribution of each tool type on the island suggests a unique origin, rather than multiple independent inventions.
The crow has "developed the capacity to evolve its tools," said Hunt, an important step in the direction of a complex material culture, like that exhibited by people.
This is an extremely interesting and well conducted study, commented Alex Kacelnik behavioral ecologist at the University of Oxford in England. There is no similar [non-human] example of cumulative transmission of a skill such as the making of pandanus [tree] leaf tools by New Caledonian crows, he said.
Kacelnik is one of the co-authors behind last year's report detailing the striking tool-making capabilities of the captive crow called Betty.
Unfortunately, We still don't know much about the process of cultural transmission and hence of what is special in these animals, to make them the master craftbirds that they obviously are, he said.
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