One of my favorite locations in Japan is an uninhabited island just off the coast of the Izu Peninsula in Shizuoka Prefecture to the south of Tokyo. Uninhabited by humans, it is, however, inhabited by another primate: a troop of Japanese macaques.

Some friends and I have several times swum over to the island to explore it, though the first time we were almost repelled by stones rolling and bouncing down the sheer cliff face — stones launched by monkeys.

Among our group, the discovery earned the habitation the name Monkey Island, and ignited in me a continuing fascination with the animals. Sure, I knew they were nicknamed "snow monkeys" for their habit of taking outdoor winter baths in hot springs. They are the most northern-living of the world's nonhuman primates, so it is perhaps not surprising that they have learned to make use of volcanically heated pools in Japan. And I also knew of the famous story of Japanese macaques washing sweet potatoes in the sea before eating them.