They look narrow them paths, also do you know if the think is no fence to stop people straying is down to lemurs at other zoos with walk throughs often sitting on them?
@taun The goal is definitely to try and keep the public away from the lemurs, and they're trying all sorts of things. The lack of fencing, which as you say lemurs always sit on, is clearly one of them. The cobbles, albeit something of a trip hazard (or throw hazard if you're a naughty child) provide another subtle barrier.
I was within a few feet of a lemur yesterday and if I had been one of those naughty children (or reckless adult) I could've been a lot closer, so how long it'll work remains to be seen.