The Celebes crested macaque (Macaca nigra), also known as the crested black macaque, Sulawesi crested macaque, or the black ape, is an Old World monkey that lives in the Tangkoko reserve in the northeastern tip of the Indonesian island of Sulawesi (Celebes), as well as on smaller neighboring islands. Description Locally known as yaki or wolai, its skin and hairless face is, with the exception of some white hair in the shoulder range, entirely jet black. Unusual for a primate, it has striking reddish-brown eyes. The long muzzle with high cheeks and the long hair tuft, or crest, at the top of the head are remarkable features. It has an "apelike" appearance due to its almost non-existent, non-visible, vestigial tail stub of only approximately . With a total body length of to and a weight of to , it is one of the smaller macaque species. Its life expectancy is estimated at 15–20 years in the wild. Ecology The Celebes crested macaque is a diurnal rain forest dweller. This macaque is primarily terrestrial, spending more than 60% of its day on the ground foraging for food and socializing, while sleeping and searching for food in the trees. The Celebes crested macaque is frugivorous, with 70% of its diet consisting of fruits. It also consumes leaves, buds, seeds, fungus, small birds and bird eggs, insects (such as beetles and caterpillars) worms, snails and the occasional small lizard or frog. Group behavior It lives typically in groups of five to twenty-five animals, and occasionally in groups of up to seventy-five animals. Smaller groups have only a single adult male, while larger groups have up to four adult males. However, adult females always outnumber adult males by about 4:1. Young adult males are forced to leave their birth group upon maturity, sometimes forming bachelor groups before seeking a connection to an existing adult mixed-sex group. Communication consists of various sounds and gestures; such as the presentation of the long canine teeth while grimacing, a clearly threatening gesture. The Celebes crested macaque is promiscuous, with both males and females mating multiple times with multiple partners. The receptivity of the females is clearly indicated by an extreme tumescence (swelling) and redness of their buttocks which, in contrast to the black skin color, is particularly noticeable. The gestation time is 174 days, and the birth of the usually single offspring happens in the spring when food