Primate location preference in a double-tier cage: The effects of illumination and cage height (2009)

MacLean, E. L., Roberts Prior, S., Platt, M. L. et al.

Abstract

Across conditions, monkeys showed a strong preference for the upper row of a standard double-tier cage. If financial or spatial constraints require that some animals be housed in the lower row, we suggest providing these animals with regular access to a multilevel activity module. ...The results of this study demonstrate the importance of providing captive macaques with access to elevated space. The illumination of lower row cages can easily be increased to match that of upper row cages with the installation of wall-mounted lights that illuminate lower row cages from behind.