Kaumanns, W., Schenmann, U. 1997. Requirements for cebids. Primate Report 49, 71-91.

Arboreal species need cages and enclosures which allow a differentiated moving in the vertical dimension. They should be able to use spatial positions which are above the level of the position of certain groupmates and of threatening humans or potential dangerous events in their environment. Cage positions in a keeping room below the eye level of human can be a source of permanent stress, because they are incompatible with adaptive tendencies of arboreal primates to avoid risks by using higher parts of the habitat.