The wide variety of altitudinal and climatic conditions have given rise to different forest types which create corresponding natural shelter, food etc. to varieties of wildlife.
It is perhaps the only state which harbors four major cats i.e. tiger, leopard, clouded leopard and snow leopard and also rare lesser feline species like the Golden cat and marbled cat. Seven species of primates i.e. hoolock gibbon, slow loris, Assemese macaque, stumptailed macaque and capped langur have been reported from Arunachal Pradesh.
All the three goat antelopes occurring in India i.e. serow, goral and takin occur in Arunachal Pradesh. Arunachal Pradesh is the only place in India where takin is found.
Highly endangered species like hispid hare have been reported from the low latitudinal grassy areas of Arunachal Pradesh.
Among the large mammals mittan, which is a cross between the wild gaur and domestic cattle, buffalo and elephant are found in the plains and adjoining hills.
The other high altitude animals include musk deer, bharal, Himalayan black bear, red panda etc. The musk deer occurs at high altitudes throughout the state, whereas the bharal has been reported occurring in the western part of the state.
Among the lesser mammals large number of rodents (squirrels, porcupine and rats), civet, mongoose, linsang, shrew and bat species occur here.
More than 500 bird species have been recorded in Arunachal Pradesh, many of which are highly endangered and restricted to this state e.g. White winged duck, sclater monal, temminck's tragopan, Bengal florican. This is the richest state in pheasants with some 10 species occupying different levels from plains to snow clad mountains.
Arunachal Pradesh is equally rich in reptiles, amphibia and pisces. Pythons and snakes of all colors and descriptions merging with their surroundings are commonly found in forests at almost all levels upto the temperate zone.
The invertebrate faunal communities are in dense and evergreen forests of Arunachal Pradesh and are in dense and evergreen forests of Arunachal Pradesh and are to be seen to be believed. Numerous species of butterflies, moths, beetles and all other kinds of small creatures make Arunachal Pradesh a paradise for entomologists and naturalists.