When I made my visit in October, that ibis was perched on a branch when a Roseate Spoonbill perched right next to him. Then the spoonbill started harassing the ibis, biting it's leg, until the ibis flew away. Poor ibis.
The enclosure for the red ruffed lemurs isn't as large as it might appear, they've cleverly added mirrors in certain places to make the exhibit appear larger. Also, there is an extremely high density of lemurs in there (around 7 or 8 on my last visit). The zoo probably doesn't want to risk putting the ibis into that setting.