Old World Monkeys: Cercopithecidae

Physical characteristics: Rhesus macaques have long, brown hair with pale brown undersides. The hair at the top of the head is short. Facial skin is pinkish, while the rump is red. Males are slightly bigger than females, weighing about 17 pounds (7.7 kilograms) and measuring 21 inches (53 centimeters), with a tail length of 10 inches (24.5 centimeters). Females are about 11.8 pounds (5.4 kilograms), measuring 18 inches (45 centimeters), with a tail length of 9 inches (22 centimeters).

Geographic range: Rhesus macaques are found in Afghanistan, Pakistan, India, Nepal, Bhutan, Bangladesh, Myanmar, China, Thailand, Laos, and Vietnam.

Habitat: Rhesus macaques are adaptable, able to thrive in mangrove swamps, cedar-oak forests, woodlands, semi-desert scrub forests, forests along rivers, and even human settlements.

Diet: Rhesus macaques eat fruits, seeds, leaves, flowers, grasses, roots, bark, gum, and insects.

The Rh factor in humans is named after the rhesus macaque, which was first discovered to have this substance in its blood. (Illustration by Barbara Duperron. Reproduced by permission.)

Behavior and reproduction: Rhesus macaques live in groups of eight to 180 individuals, although the average size is about twenty, with two to four times as many females as males. There are dominant males and females within a group, with the offspring inheriting the mother's rank. Macaques are arboreal but descend to the ground to forage and to move among human settlements. They prefer to sleep in the trees at night. They communicate through facial expressions, body language, and vocalizations, including barks, squawks, and growls. Adults have several partners. Females give birth to a single infant annually. Females remain with the group, while males may transfer from one group to another.

Rhesus macaques and people: The Rh factor in humans is named after the rhesus macaque, which was discovered to have this substance in its blood. Rhesus macaques are popular zoo animals. Farmers consider them pests for eating crops.

Conservation status: The IUCN lists the rhesus macaque as Near Threatened, meaning it could become threatened, due to hunting and habitat loss and degradation from human activities. ∎