Chimps 'solve puzzles just for fun'
Just like human crossword addicts, chimpanzees love having their brains teased, research has shown.
The apes enjoy getting stuck into a puzzle - with or without the opportunity to win a prize.
Scientists at Whipsnade Zoo, Bedfordshire, set up a game for six chimps that involved moving red dice through a network of pipes until they fell into a container. To achieve their goal, players had to prod sticks into holes in the pipes to change the direction of the dice.
The same task was also carried out using brazil nuts instead of dice, so that success led to a tasty treat.
Researcher Fay Clark, from the Zoological Society of London, said: "We noticed that the chimps were keen to complete the puzzle regardless of whether or not they received a food reward. This strongly suggests they get similar feelings of satisfaction to humans who often complete brain games for a feel-good reward."
The chimpanzees, all members of an adult family group at the zoo, did not receive advance training on how to play the game. "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 to not stick to the tool," said Ms Clark.
The findings are published in the American Journal of Primatology.
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 apes were given complete freedom whether or not to pit their wits in the puzzle, said the scientists. They chose to take part in the game despite also receiving treats hidden in boxes as part of the zoo's enrichment programme.
Like humans, chimpanzees are motivated to solve a puzzle for its own sake, without needing a food reward, said the researchers.