Odd, they have quite a few including a baby and they're pretty showy. Did you go to all the viewings areas for the exhibit or just this one? They're usually by here but sometimes wonder to the far end of the enclosure.
In the winter the geladas have access to their indoor/heated enclosures off exhibit. They could have been there; but I have sometimes only seen the entire troop all right against the glass of one of the viewing huts.
