 The biomes on Bioko Island are typically categorised into three subtypes; tropical rainforests in the lower regions, montane forest, which is typified by higher humidity, a lower temperature, and is dominated by tree ferns, and mossy forests at highest altitudes.While the Bioko drill will preferentially inhabit lowland forests, tending to larger groups in these areas, populations have been found inhabiting areas up to 2,000m above sea level in grasslands and areas with dense undergrowth.Lowland populations tend to be more diverse, potentially due to a higher diversity of vegetation, with fruits more prevalent at lower altitudes and higher altitudes more conducive to more fibrous sources of food such as herbs and ferns.