Sierra Leone's most visited natural reserve is home to over 700 different plant species, 135 bird species (including eight species of hornbill), plus otters and sea turtles. Tiwai is most famous for its primate population – the forests are home to the striking black-and-white Diana monkey as well as chimpanzees. The endangered, elusive pygmy hippopotamus is also a resident here – of the estimated 2000 left in the wild, they are only found in Sierra Leone, Liberia, Guinea and Côte D'Ivoire.