@David Matos Mendes The guenon was actually (unintentially of course) doing some invasive species control .
No, I'm not 100% sure but I wouldn't think guenons wouldn't be able to be kept with smallish birds as like most monkeys they will occasionally eat adults of these in the wild if they can catch them (more frequently their eggs and nestlings though).
Yes, this was a wild bird that flew into the exhibit and got a little too close to the guenon. And in Australia these birds are considered a noxious invasive.