This study is based in Tana River National Primate Reserve (TRNPR), Kenya. The reserve, established in 1976 to protect remnant patches of riverine forests from increasing human pressure is home to two endemic endangered primate subspecies, Tana River Red colobus (Colobus badius rufomitratus) and Tana River Crested mangabey (Cercocebus galeritus galeritus). Habitat encroachment through indigenous farming and forest uses was thought to be one of the causes of drastic colobus and mangabey population decline after 1975. This study aimed at; generating information on the impact of these human land-uses on the habitat, this would facilitate the preparation of management recommendations which would improve the chances of survival of primate habitats without compromising the welfare of indigenous people. Using 3 sets of aerial photographs and a geographic information system, information on land-use changes over time has been generated. A 3 month field work generated information on agriculture, forest uses and other relevant socio-economic information. Results from the study indicate that: (i) human population has increased by more than two-folds between 1969 and 1991; (ii) this has not corresponded to a net increase in forest area decrease or farm area increase; (iii) there has been a net increase in area under forest and decrease in area under agriculture; (iv) spatial and temporal changes in forest area explain colobus population crash observed between 1975 and 1985, (v) indigenous farmers interviewed prefer a compromise, where they are allowed controlled access to land within the reserve. They showed a keen knowledge of conservation costs and benefits and cause-effect processes between humans and the environment. Management recommendations advocate measures that encourage indigenous people to be partners in conservation.