Wakenshaw, V. 1999. The management and husbandry of Geoffroy's marmoset. International Zoo News 46(1), 3-15.

A survey of selected enrichment programs for group-housed marmosets. Older individuals ... appear to habituate themselves less to the presence of visitors, and get very agitated when approached. ... High perches should be provided to give animals vantage points from which to look down onto the visitors, restoring some level of control.