The white-faced saki (Pithecia pithecia), is a species of New World saki monkey. The small bodied neotropical primate can be found in Brazil, French Guiana, Guyana, Suriname, and Venezuela. This species feeds mostly on fruits, nuts, seeds, and insects. Although it is an arboreal species and is a specialist of brachiation, it is also terrestrial when foraging. Typical life expectancy is around 14 years in its natural habitat, although individuals have been recorded to live up to 36 years in captivity. The white faced saki is active in the day and sleeps highly elevated (15–20 m (49–66 ft)) in trees with many leaves to shelter from weather and flying predators. A formerly recognized subspecies, P. p. chrysocephala, was elevated to full species status as P. chrysocephala in 2014.
Reproduction and sexual dimorphism
Pairs of white-faced saki only breed once a year, but do not breed seasonally. Estimated typical breeding season is through August and September, but white-faced sakis have been observed breeding in March, April, and June. Breedings are typically not private and are sometimes even done with other group members watching. Regardless of when or how reproduction occurs, a white-faced saki female only gives birth to one offspring at a time. Peak birth months typically occur between February and June. In captivity, female white-faced sakis experience ovarian cycles of approximately 17 days, and a gestational period of 20–21 weeks. Following birth, the mother undergoes a period of lactationally-induced infertility lasting 23 weeks on average. Once an infant is born, the father spends a great deal of time around it and the mother, likely to protect the two from predators. During this time the mother grooms and takes care of its offspring until it becomes independent. Male paternal care on the other hand does not exist at all. Once it is independent, the offspring usually stays and contributes as a member of the group it was born in. Mature females that are still housed by their parents do not participate in reproduction. White-faced saki practice both monogamy and polygamy, and are defensive when it comes to keeping other groups away from their females. As such, there are only two objectives to the white-faced saki mating system: 1) exclude outsider groups from accessing their females and 2) reduce competition within the group over females. White-faced sakis display noticeable sexual dimorphism in coloration. Females have shorter hair than males, with brownish-grey fur and white or pale brown stripes around the corners of the nose and mouth. Males, on the other hand, have blacker fur, with a reddish-white forehead, face, and throat. Their faces are much whiter than those of females. When compared in size, there is little to no difference between a male and a female white-faced saki. In the species, both genders have relatively small bodies with males typically weighing in around 1.73 kg (3.8 lb) and females weighing in around 1.52 kg (3.4 lb). In terms of hierarchy, males are clearly favored within the group and its social bonds. Typically, the oldest male is the most dominant in a group. Young saki males are often identified as females because of their sometimes "grizzling" dorsal hair and orangish bellies. It is at approximately 2 months of age when males and females begin to show differences, although it gradually becomes obvious over a few years.
Behavior and social bonds
The white-faced saki typically exhibits shy behavior. It is most active during the early morning and mid-afternoon, and can be found in the understory and lower canopy of the rainforest. Males are usually more active than females. At night, the white-faced saki typically migrates up hills to higher altitudes to sleep near the tops of trees. It typically changes its sleeping site every night except on rare occasions. The white-faced saki separates themselves into small family-like groups. A South American study shows that groups can range from 2-12 group members, with higher numbers typically occurring (but not exclusively) in Guyana. Most widespread observations conclude that the white-faced saki travels in small groups of 2 and 3, which usually is made up of the bonded parents and their offspring. It is believed that it practices both monogamy and polygamy. It is uncertain which one is practiced more, but single male and single female white-faced saki bonds are the strongest bonds witnessed within the groups. The white-faced saki typically strengthens and demonstrates this bond through grooming. However, only the females groom males, and the males do not reciprocate. This practice occurs less frequently after an infant is born. As the child becomes more independent, the father and mother spend less time together, and the mother grooms the father less. Male-male bonds between white-faced saki are the weakest. When polygamy is practiced within groups, competition between members can arise. In some cases, members may even interrupt one another while reproduction is occurring. These conflicts that occur within groups are nowhere near as intense as the conflicts that occur between two different groups. White-faced sakis are typically peaceful when in the presence of other species of primates, but when in the presence of a different group of white-faced sakis, they become very hostile. These encounters usually lead to standoffs and loud calls between groups. At times these standoffs can even lead to white-faced sakis chasing one another from tree to tree, causing deaths of some participants who have fallen out of a tree. The reason behind this hostile behavior between groups is usually over access to females. White-faced sakis want to keep access to females exclusive to their group. However, altercations between groups can also occur over resources and food. Even though groups are typically hostile to white-faced sakis outside the group, they do sometimes allow immigrant white-faced sakis to become members of the group.
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