Crab-eating macaque 27% animal matter, 15% flowers and other plant matter, and 14% food provided by humans. This species exhibits particularly low tolerance for swallowing seeds. Despite their inability to digest seeds, many primates of similar size swallow large seeds, up to , and simply defecate them whole. The crab-eating macaque, though, spits seeds out if they are larger than . This decision to spit seeds is thought to be adaptive; it avoids filling the monkey’s stomach with wasteful bulky seeds that cannot be used for energy. It also can help the plants by distributing seeds to new areas: Crab-eating macaques eat
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.