Kalimantan's flora and fauna are among the most diverse in the world. You can find more tree species in a single hectare of its rainforest than in all of the US and Canada combined. There are more than 220 species of mammals and over 420 species of birds found on Borneo, many of them endemic to the island. The region is best known for its orang-utans, Asia’s only great ape and a rare but thrilling sight outside of Kalimantan's many rescue and rehabilitation centres. River cruising commonly reveals proboscis monkeys (unique to Borneo), macaques, gibbons, crocodiles (including gharials), monitor lizards and pythons. Hornbills are commonly seen flying overhead, and are a spiritual symbol for many Dayak. Forests harbour the rare clouded leopards, sun bears, giant moths, tarantulas and more bizarre species of ants and spiders than you could ever conjure out of your wildest imagination. For divers the Derawan Archipelago is renowned for its turtles, manta rays and pelagics.