Several groups of nonhuman primates including macaques, chimps, and capuchins have found a way to use rocks to secure new food sources. However, a new study in eLife has shown that the long-tailed macaques of Khao Sam Roi Yot National Park in Thailand are threatening to drive shellfish populations extinct with their tools. The monkeys use rocks to smash and pry open the largest oysters, crabs, and snails they can find. The result of their systematic hunting has been an overall decrease in the average size of their prey, shrinking one species of oyster by as much as 70% compared with locations without the macaque pressure, New Scientist reports. If the monkeys don’t slow down, they may deplete the islands of their food source, and if that happens, they may even forget how to use their stone tools over subsequent generations because the use of technology is a learned behavior passed from one animal to the next.