Rainfall is uneven and continues throughout the year though the wettest periods of the year are the months of May to September. The wide variety of altitudinal and climatic conditions account for the creation of different types of forests whose natural shelter and food harbor a range of fauna, some of which are peculiar to Arunachal Pradesh. More than 500 bird species have been recorded, many of which are highly endangered and restricted to this state like the white-winged duck, sclater monal, Bengal floricans, etc. This is the richest area for pheasants whose species vary with the different levels from the plains to the snow-clad mountains. Besides, there are seven species of primates including takin which is to be found only in Arunachal Pradesh.
Individual wealth is reckoned in terms of the number of mithuns possessed.
Mithun counts for cash transactions and is looked upon as a precious part of a dowry. Arunachal Pradesh has an equally rich variety of reptiles, amphibian, and pisces. Pythons and snakes are commonly found in forests in the temperate zone. Arunachal Pradesh also has national parks and sanctuaries where strict rules are followed for the preservation of its rare fauna. There is not much information available on the history of Arunachal Pradesh.