The WWF estimates that the island has at least 222 species of mammals (44 of them endemic), and 13 species of primates. Among mammals, bats and rodents abound, due to the networks of caves and characteristic of Borneo rainforest. These species are very useful for their function of dispersing seeds and controlling insect populations. The orangutan is the main species and is exclusive to Borneo and Sumatra, the neighboring island. Other mammals include the proboscis monkey, the Müller gibbon of Borneo, the Malayan bear, the nebulous leopard, the elephant of Borneo, the Borneo rhinoceros and the banteng, a species of wild cattle widespread in Southeast Asia.

In Borneo there are about 420 resident birds (37 endemic); 100 amphibians; 394 fish (19 endemic). Among the birds, the eight species of calaos stand out, symbols of the island due to their variety, size, color and quantity. As for the insects, 1,000 single insect species have been found in a single dipterocarp tree. All these species have suffered great losses of their population due to the destruction of their habitats during the deforestation of the island. It is hard to quantify the number of casualties and perhaps you will never know how many died in the large fires or in their failed attempts to adapt to the island’s new vegetation, especially oil palms.