Kerridge, F. J. 2005. Environmental enrichment to address behavioral differences between wild and captive black-and-white ruffed lemurs (Varecia variegata). American Journal of Primatology 66, 71-84.

Behavioral enrichment experiments were carried out in which whole rather than chopped fruit was provided and presented in a more naturalistic manner [whole fruit suspended by sisal or jute from wooden polses]. ... Manual manipulation of dietary items increased. Time spent feeding also increased significantly. .. The novel feeding method successfully stimulated the animals to use their hands to obtain and process fruit. It also necessitated bipedal and tripedal suspension. .. The enrichment increased the time spent feeding to levels similar to those seen in the wild.