The woodpecker finches of the Galpagos Islands show no sign of learning their considerable tool-using skill by copying each other.
The finches poke twigs or cactus spines into crevices to dig out insects, explains Sabine Tebbich of the Max Planck Institute for Behavioral Physiology in Seewiesen, Germany. The birds seem to consider the challenges of a particular crevice as they select a probe, sometimes stripping off a leaf that would keep a twig from sliding deep.
Not all birds of this species, Cactospiza pallida, use probes. However, Tebbich now reports that a non-tool-user doesn’t seem to pick up the skill by imitating an accomplished finch. Instead, the birds show a predisposition to fiddle with twigs during a sensitive period as juveniles. In the right environment, they seem to develop proficiency largely through trial and error, Tebbich and her colleagues report in the Nov. 7 Proceedings of the Royal Society of London B.
These results are “very much to our surprise,” says coauthor Michael Taborsky of the University of Berne in Switzerland. “Even though it is quite complex behavior, it does not mean that [imitation] has to be involved.”
Plenty of animals use tools. Among birds, for example, Egyptian vultures toss rocks at ostrich eggs until the shells break. Green-backed herons sometimes drop bits of food into a stream as bait, repositioning it if currents start to sweep it away. Before the new finch work, however, experiments hadn’t investigated how birds pick up such skills, according to Taborsky.
Among woodpecker finches, birds in the dry areas probe with tools more frequently than birds in humid areas do, the researchers report.
By pairing an accomplished finch with each of 10 adults that hadn’t used tools, Tebbich offered a 2-week apprenticeship. Tested daily during the training only one in the non-user group managed to scrape out a snack with a twig–and that bird had already played with twigs.
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To check skill development in fledglings, Tebbich paired some youngsters with accomplished adults and others with unskilled birds in aviaries containing twigs and hidden snacks. Regardless of which mentor the youngsters had, all the young birds figured out the technique.
As she watched the young finches grow up, Tebbich noticed stages of experimentation with twigs. Over a month or two, the birds started by biting the ends of twigs on bushes and ended by capturing an insect.
A bird in a humid zone with abundant insects probably wouldn’t find such experiments rewarding, the team says. But a finch in a dry, food-poor area would gain a lot by stumbling on tool use.
The scenario makes sense, according to Sara J. Shettleworth of the University of Toronto. “Very often you see animals preprogrammed with some kind of rough unskilled behavior,” she says. As such animals fumble around, “the environment teaches them,” she says.