Researcher Fay Clark, from the society, said they noticed the chimps were "keen to complete the puzzle" for its own sake, regardless of whether or not they received a food reward.This is yet another example that we think in the same was as out fellow apes - the main difference being that we have bigger brains (which can store very much more information) and we can also far more effectively pass information from one individual to another using language.
"This strongly suggests they get similar feelings of satisfaction to humans who often complete brain-games for a feel-good reward," she said.
"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."
Researchers created higher "levels" of challenge by connecting many pipes together, and making them opaque so the dice or nuts could only be glimpsed through small holes.
The full article, Effect of a Cognitive Challenge Device Containing Food and Non-Food Rewards on Chimpanzee Well-Being, is published in the American Journal of Primatology, and contain useful information and prior references to related work.