Habitat enrichment - primates. Animal Welfare in Captivity and Environmental Enrichment book. Download free in English and/or Spanish on: https://www.scribd.com/collections/5757077/Animal-enrichement-and-welfare https://www.academia.edu/8754986/Environmental_Enrichment_and_Well-Being_of_Captive_LATAM_Mammals https://www.academia.edu/8755049/Enriquecimiento_Ambiental_y_Bienestar_de_Mam%C3%ADferos_en_Cautiverio
Tennis Ball Feeder for Swamp Monkeys at Saint Louis Zoo. Such a fun idea with a Great picture where you can really see how it fits together. I would put a hinge and locks at the bottom for easier cleaning however.