Do birds build up better tool designs? (Techno Crow).
The crow Corvus moneduloides fashions tools for snagging insects from crevices. New Zealand researchers surveyed a kind of tool cut from the edge of a stiff leaf. They found a location where crows use all three known tool types, a surrounding zone where they use two types, and the greatest expanse featuring only one, report Gavin Hunt and Russell Gray of the University of Auckland. The most widely distributed tool appears to be the most sophisticated.
This pattern suggests that the crows developed the basic leaf tool once and then improved it over generations, Hunt and Gray contend in an upcoming Proceedings of the Royal Society of London B.
"As far as we know, it's the first report in a species other than humans of cumulative change of tool design," says Hunt.
The idea of cumulative tool improvement "seems perfectly plausible," comments Alex Kacelnik, who studies the same crow species in his laboratory at Oxford University in England. Yet he cautions that before fully accepting such a bold claim, researchers still need to show that birds learn detailed techniques from each other.
The old notion that people are the sole users of tools has collapsed in recent decades in response to reports of tool-wielding chimps, orangutans, and Galapagos woodpecker finches.
Hunt happened upon the crows' tool-making in the mid-1990s. Although New Caledonian crows are hard to observe directly, Hunt and Gray analyzed the edges of straplike pandanus leaves left behind on trees after a bird has cut out its tool.
The researchers have now collected data on some 5,550 pandanus-leaf tools. They report three types of strips--wide, narrow, and tapered with steps cut along one side. Each shape requires a different sequence of rips and snips. The variety of processes suggests cumulative tool development, the researchers say.
In human technological advancement, "you don't make the old cell phone and then modify it to a new design," says Hunt. A manufacturer instead works out a new plan for making the improved model.
Hunt argues that the most probable explanation for the crow-tool zones is that improved designs radiated from a center of discovery. If the tools had multiple origins, he'd predict a patchwork distribution. He finds no correlation between major ecological factors, such as rainfall, and the zones of different designs.
Christophe Boesch of the Max-Planck Institute for Evolutionary Anthropology in Leipzig, Germany, raises the alternative possibility that different functions for tools in different places might explain the zones. He'll soon publish a report proposing that chimps accumulate tool improvements.
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|Date:||Mar 22, 2003|
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