Macaca fascicularis Skull measures 3.9 inches Macaca fascicularis Skull is museum quality polyurethane resin cast. Known as Crab Eating Macaque Monkey

Macaca fascicularis or Crab Eating Macaque Monkey live in social groups that contain three to 20 females, their offspring, and one or many males.

The groups usually have fewer males than females. In social groups of macaques, a clear dominance hierarchy is seen among females. These ranks remain stable throughout the female’s lifetime and also can be sustained through generations of matrilines.

Females have their highest birth rates around 10 years of age and completely stop bearing young by age 24.

The social groups of Macaca fascicularis or Crab Eating Macaque Monkey are female-bonded, meaning the males will disperse at the time of puberty. Thus, group relatedness on average appears to be lower than compared to matrilines.

More difference in relatedness occurs when comparing high-ranking lineages to lower ranking lineages, with higher-ranking individuals being more closely related to one another.

Groups of dispersing males born into the same social groups display a range of relatedness, at times appearing to be brothers, while at other times appearing to be unrelated.

In addition to the matrilineal dominance hierarchy, male dominance rankings also exist. Alpha Macaca fascicularis or Crab Eating Macaque Monkey males have a higher frequency of mating compared to their lower-ranking conspecifics.

The increased success is due partially to his increased access to females and also due to female preference of an alpha male during periods of maximum fertility.

Though females have a preference for alpha males, they do display promiscuous behavior. Through this behavior, females risk helping to rear a non-alpha offspring, yet benefit in two specific ways, both in regard to aggressive behavior. First, a decreased value is placed on one single copulation. Moreover, the risk of infanticide is decreased due to the uncertainty of paternity.

Increasing group size leads to increased competition and energy spent trying to forage for resources, and in particular, food. Further, social tensions build and the prevalence of tension-reducing interactions like social grooming fall with larger groups. Thus, group living appears to be maintained solely due to the safety against predation.

Macaca fascicularis or Crab-eating macaques sometimes form mixed species groups with other primate species, including the southern pig-tailed macaque, dusky langur and white-thighed surili. They have been observed engaging in grooming with other primate species.