Animal testing on non-human primates between the monkeys natural behaviors versus the behaviors expressed by the diazepam induced monkeys in thirteen different locations inside the maze. Scientist Barros and his colleagues created this model to allow the monkeys to roam a less confined environment and slightly eliminate outside factors that may induce stress. Many of the best-known allegations of abuse made by animal protection or animal rights groups against animal-testing facilities involve NHPs. The so-called "pit of despair" was used in experiments conducted on rhesus macaque monkeys during the 1970s by American comparative psychologist Harry Harlow at the University of Wisconsin–Madison.<ref name="Blum1994/95">Blum, Deborah. "The Monkey
Celebes crested macaque Paignton Zoo are among a number of mostly European zoos which hold "ex-situ" breeding populations of this animal. Since 2006, the "Macaca Nigra Project" has been studying the biology and promoting the conservation of this species. The project, a collaboration between the German Primate Center and the Bogor Agricultural Institute, is run by Antje Engelhardt and located in the Tangkoko reserve, home of the biggest crested macaque population remaining in the species' original distribution range. Nevertheless, despite being critically endangered, crested black macaque are still being hunted down and slaughtered. Crested black macaque is considered a delicacy by local residents.