Cercopithecus erythrotis is an arboreal species found in lowland tropical forests. Cercopithecus e. erythrotis is found in lowland forests from sea level across the elevational gradient on Bioko through montane forests to the subalpine scrub zone found at the top of Pico Basilé at 3,011 m asl (Butynski and Kingdon 2013). Preferred habitat is primary lowland forests (e.g., southern and southwestern Bioko) (González-Kirchner 1996), where the monkey's abundance is at its highest (Cronin et al. 2016). The areas where it is present receive a gradient of rainfall from 2,000–10,000 mm, which include the ‘monsoon forests’ of southern Bioko (Oates et al. 2004).

Cercopithecus e. camerunensis is also found predominantly in primary lowland tropical and submontane moist forest. It prefers mature forests to young secondary forests, probably to reduce competition with the Mona monkey (C. mona), which specialises in disturbed and edge forests (Oates 2011). The species feeds and travels lower in the canopy than other arboreal guenons (Oates 2011). In Cameroon, group sizes of about 4 to >29 animals have been reported (Struhsaker 1969) and feeds on fruit, supplemented with leaves, shoots and arthropods (Gartlan, & Struhsaker 1972, Zinner et al. 2013).

This species is listed on Appendix II of CITES and on Class B of the African Convention on the Conservation of Nature and Natural Resources.

The species is protected by national legislation in Cameroon and Nigeria. It occurs in a few protected areas, including Korup National Park, Takamanda National Park, Mount Cameroon National Park, the proposed Ebo National Park, and Bayang-Mbo Wildlife Sanctuary. In Nigeria, it occurs in Cross River National Park and Afi Mountain Wildlife Sanctuary. Outside protected areas, it is found at several sites along the Cameroon-Nigeria border including Mawambi Hills, Mone Forest Reserve and the adjacent Mbulu-Mt. Oku Complex (in Cameroon), and Mbe Mountains, Iko Esai Forest and Ekuri Forest (in Nigeria). Cercopithecus e. camerunensis shares its habitat with many other endangered primates, including the Cross-River Gorilla (Gorilla gorilla diehli), the Nigeria-Cameroon Chimpanzee (Pan troglodytes ellioti), and the Drill (Mandrillus leucophaeus), and may indirectly benefit from conservation activities aimed at protecting these species. However, hunting levels remain high both inside and outside protected areas (e.g. Linder et al. 2011, Ajonina et al. 2014). The ‘Anglophone crisis’ in Cameroon likely exacerbates threats to this species, particularly concerning bushmeat hunting, and hinders conservation for this, and other species.

In Bioko, this species is also protected by national legislation. The majority of its population is found within Bioko’s two protected areas (IUCN: Ib - Gran Caldera Scientific Reserve; II – Pico Basilé National Park), in which hunting is prohibited (Republic of Equatorial Guinea 2003). Furthermore, the hunting, sale, and consumption of primates was banned by Presidential Decree in October 2007 (Republic of Equatorial Guinea 2007), however, hunting pressure is intense and occurring throughout both protected areas (Cronin et al. 2013, 2016; Grande-Vega et al. 2013, 2016).

The Bioko Biodiversity Protection Program have projects underway within the Gran Caldera Scientific Reserve, including primate monitoring, alternative livelihoods, educational programs, professional development training (i.e., ecoguard training), the development of a Nature Center in the village of Ureca, and partnering with INDEFOR-AP to foment their active involvement in the reserve and its day-to-day management. A United Nations Development Programme – Global Environmental Facility project is also ongoing on the island with the goal of strengthening Equatorial Guinea’s system of protected areas. Work has also begun in Pico Basile National Park by the NGO, Ecoguinea, putting forth studies on socioeconomic factors driving bushmeat consumption in the villages bordering the park and other research (e.g., Grande-Vega et al. 2013, 2016). This group has also conducted a number of educational outreach campaigns about bushmeat and conservation in order to reduce hunting pressure, and is working with INDEFOR-AP to develop a system of forest patrols for the park.