Just as you or I might enjoy doing a crossword puzzle, so too do chimps enjoy completing tricky puzzles, just for the hell of it.
Scientists from the Zoological Society of London set up a challenge for six chimpanzees at Whipsnade Zoo, using plumbing pipes from a DIY store.
The challenge involved moving red dice through a network of pipes until they fell into an exit chamber, and could only be achieved by the chimps prodding sticks into holes in the pipes to change the direction of the dice.
The same task was also carried out with Brazil nuts, but with the exit chamber removed so that the nuts fell out as a treat.
"We noticed that the chimps were keen to complete the puzzle regardless of whether or not they received a food reward," says ZSL researcher Fay Clark.
"This strongly suggests they get similar feelings of satisfaction to humans who often complete brain games for a feel-good reward."
The chimps weren't trained for the task and weren't forced to take part; it was introduced as part of their normal routine. It was made more intricate by connecting many pipes together, and the level further increased by making pipes opaque so chimpanzees could only see the dice or nuts through small holes.
"For chimps in the wild, this task is a little bit like foraging for insects or honey inside a tree stump or a termite mound; except more challenging because the dice do not stick to the tool," says Fay.
The study suggests that, like humans, chimpanzees are motivated to solve a puzzle even without a food reward - for the sake of the challenge itself.