Crows rely on tools to get their work done.

Next time you need to borrow a tool, your thoughts may turn to the crows flying overhead.

Crows on the Pacific island of New Caledonia make tools out of sticks and leaves, says ecologist Gavin R. Hunt. The birds differ from other tool-making wild animals, including other birds, in several respects, he contends: The crows make two types of tools, the implements show "a high degree of standardization," and the tools have hooks and barbs.

Humans' stone and bone tools lacked these features until about the time Homo erectus appeared, reports Hunt of Massey University in Palmerston North, New Zealand. Tools used by chimpanzees also lack these features, he says.

"It's very interesting to see that crows can make different tools for different purposes," says Christophe Boesch of the University of Basel in Switzerland. "But Hunt went a bit far when he claimed these tools represent standardization and abilities that haven't been observed in [other wild] animals."

Hunt watched the New Caledonia crows, Corvus moneduloides, using twigs or leaves as tools on 52 occasions between November 1992 and March 1995, he reports in the Jan. 18 Nature. The birds usually employ the tools' hooked or narrow ends to find bugs in wood or under leaves, he reports. They carry the tools as they fly between trees or foraging locales and leave the tools at their feet or "in a secure position on their perch" when not using them.

The birds make one class of tools, which Hunt calls stepped-cut tools, from the barbed leaves of pandanus trees. He has never seen a bird making these devices, but he has collected many samples of them. They look like tapered saw blades, are slightly rigid, and range in length from 10.6 centimeters to 40 cm.

On four occasions, Hunt watched the crows make the other class of tools, which he calls hooked-twig tools. A bird pulls a twig off one of a variety of trees. Using its beak, it forms a point at the hooked end of the twig. It also strips off the leaves and usually the bark.

The hooked-twig tools Hunt collected at a site on Mount Cindoa averaged 15.9 cm in length; those from a site on the mountain Pic Ningua averaged 13.3 cm.

Scientists have described tool use by 36 other species of birds, but only two wild birds employ tools regularly to find their prey in trees, Hunt says.

The woodpecker finch from the Galapagos Islands uses modified twigs and cactus spines. The brown-headed nuthatch in the United States detaches pieces of bark and uses them to pry off other bark. These tools require much less technical sophistication to manufacture than the devices used by the crows in New Caledonia, he says.

Crows in Scotland, Kenya, and the United States use found tools in various fashions, Hunt says. For example, in the United States, crows use "cars as nutcrackers" by dropping walnuts on the road and waiting for cars to run over them. Another member of the crow family, the raven, throws stones at intruders.

Boesch, who wrote an accompanying commentary, challenges Hunt's statement that crows make standardized tools rather than modifying them during use. He says that Hunt didn't observe enough birds making tools to know whether or not they changed their tools after trying them out.

In addition, Boesch says that chimpanzees' tools have features that Hunt claims are unique to crows' tools.