The monkeys, living in an enclosed but barrier-free environment, were taking interest in zoo visitors’ cell phones as they held them out to take pictures or video or whatnot.

Since monkeys grab things they find interesting (just like my kids), they starting snatching the cell phones. Funny stuff. The zoo trained the monkeys not to grab the phones any more. That is to be expected. But not for the reason you think:

It’s important that the monkeys maintain their natural behaviour and training them not to go for visitors’ phones was essential to achieving this.

Good grief. There’s nothing natural about living in a zoo. There never will be. Besides, if someone went walking through a forest or jungle where grabbing monkeys lived, the monkeys would probably grab their cell phones – right there in their natural habitat. Why couldn’t the reason to retrain the monkeys be so that visitors wouldn’t have their cell phones grabbed? Jeez.