As any good sculptor will attest, there is a certain art to swinging a hammer: Too little force is ineffective, but too much risks ruining the entire project. New research published today in Current Biology suggests that humans aren’t the only animals carefully controlling their hammer strikes. Scientists now say that wild bearded capuchin monkeys (Sapajus libidinosus) are carefully modulating how hard they smash one of their favorite foods—tucum nuts—to open them. Toolmaking is a well-established phenomenon in many primate species, but this level of dexterity surprised the researchers. The primates typically place the nut, which contains a hard inner shell surrounded by a softer hull, onto a hard surface and then strike it with a heavy stone. After each hit the monkeys check for damage and adjust the force of their next attempt. No damage, and the animals swing harder. Cracks, and they soften the blow. The researchers say that multiple softer strikes provide two advantages. First, the energy required for multiple “mini strikes” is lower than the energy needed for one big strike. Second, the soft, edible kernel inside the nut is more likely to survive the softer blows. But the results are not completely surprising. Researchers are increasingly finding species—from archerfish to primates—that adjust their movements based on feedback.
(Video credit: Mangalam et al./Current Biology 2015)