The island is only about 12 square kilometres - you could walk all the way around it in a few hours. But that small patch of jungle is packed with animals. Scientists have counted more than 135 different kinds of birds here, as well as eleven different species of primate, which is an extraordinary number for one tiny island.
Tiwai has been a protected wildlife sanctuary since 1987. Local communities help look after it, which means the animals trust the island as a safe place to live. Chimpanzees have been studied here for decades, and researchers have learnt a great deal about how chimps use tools, talk to each other, and raise their babies.
The river that wraps around Tiwai is part of its magic. Visitors arrive by dugout canoe, gliding quietly through water that reflects the treetops above. African manatees sometimes surface in the river, and fish eagles soar overhead looking for their next meal.