Drill pictures (Mandrillus leucophaeus), also known as Drill Baboons.
Drills, previously considered to be a baboon, are one of the largest monkeys. Males can grow to twice the size of femalres. The rainbow coloration on the male's bottom (designed to attract females) gets brighter as he gets excited. Groups consist of one male with up to 20 females.
Drills are one of Africa's most endangered primates, living only in Nigeria and Cameroon. Their range in the wild has been almost elminated due to deforestation and the killing of drills for bushmeat.