The macaque, belonging to the genus Macaca, is one of the most successful and widespread groups of Old World monkeys, second only to humans in its geographic reach. This genus encompasses a diverse array of species that have adapted to a vast range of environments across two continents. Macaques are a significant focus in primate studies due to their complex social behaviors and high adaptability, which allows them to thrive even in human-altered landscapes.
Taxonomy and Global Distribution
Macaques are classified within the family Cercopithecidae, placing them firmly among the Old World monkeys. The genus Macaca is notable for its species richness, containing over 20 currently recognized species. This contributes to the genus having the broadest geographic range of any non-human primate.
The vast distribution of macaques spans from North Africa through South and East Asia. The Barbary macaque (Macaca sylvanus) is the only species found outside of Asia, inhabiting parts of Morocco, Algeria, and the European outpost of Gibraltar. The majority of species are concentrated across the Asian continent, ranging from Afghanistan to Japan, and extending through the Indian subcontinent and Southeast Asia to the Philippines and Indonesia.
The Rhesus macaque (Macaca mulatta) is particularly widespread, found across a large area from Afghanistan through northern India and down to Vietnam. Their extensive range includes tropical regions, subtropical forests, and temperate zones.
Diverse Habitats and Physical Adaptations
Macaques occupy an extensive variety of habitats, including dense tropical rainforests, coastal mangrove swamps, temperate deciduous woodlands, and high-altitude mountain ranges. This environmental flexibility is supported by a range of physical adaptations.
The Japanese macaque (Macaca fuscata), or Snow Monkey, survives winter temperatures as low as -15°C in the colder, mountainous regions of Japan. Their survival is aided by a dense coat of fur, which provides insulation. Conversely, the Long-tailed macaque (Macaca fascicularis) is highly adapted to riverine and coastal environments, often inhabiting mangrove swamps and nipa palm forests.
Physical traits reflect varying degrees of arboreality and terrestrial movement. Most macaques are semi-terrestrial, spending considerable time on the ground. Highly arboreal species, like the Long-tailed macaque, use their long tails for balance while navigating the canopy. Other species, such as the Stump-tailed macaque (Macaca arctoides), have very short tails, associated with a more terrestrial lifestyle. All macaques possess cheek pouches for temporarily storing foraged food, allowing them to quickly gather resources before consuming them elsewhere.
Complex Social Structures and Communication
Macaques are highly gregarious primates that live in multi-male, multi-female social groups, or troops, ranging in size from ten to over one hundred individuals. The internal dynamics of these troops are governed by strict, linear dominance hierarchies. A core feature is female philopatry, meaning females remain in their birth group for life, while males typically disperse upon reaching sexual maturity.
The female hierarchy is exceptionally stable and based on kinship, establishing a matriarchal structure where rank is largely inherited from the mother. A distinctive rule is “youngest ascendancy,” where a younger sister will eventually outrank her older sisters. This system creates powerful matrilines that maintain their rank across generations, with the highest-ranking female of the highest-ranking matriline functioning as the group’s matriarch.
The male dominance hierarchy is more fluid, determined by physical prowess, age, and the formation of alliances. The alpha male maintains order and protects the troop from external threats, though the matriarch often holds the true social power over resource access and group movement. The social system is reinforced through allogrooming, or social grooming, a cooperative behavior that reduces tension and solidifies social bonds within the troop.
Macaques employ a sophisticated repertoire of visual signals and vocalizations. Facial expressions are particularly important, such as the silent bared-teeth display, which conveys different meanings depending on the species’ social style. In species with strict hierarchies, like the Rhesus macaque, the bared-teeth display is a submissive gesture used to appease a dominant individual. In more tolerant species, the same display may be used as an affiliative signal to indicate peaceful intentions. Body posture, such as presenting the hindquarters, is another common submissive signal used to acknowledge lower status.
Feeding Ecology and Anthropogenic Coexistence
Macaques are highly opportunistic omnivores. Their diet in natural settings is broad, consisting of fruits, seeds, leaves, flowers, tree bark, insects, and small vertebrates. The Long-tailed macaque is known to forage for crabs and other shellfish in coastal areas, demonstrating specialized foraging behavior.
This dietary and behavioral flexibility has led to a high degree of coexistence, allowing macaques to successfully live alongside human populations. Species like the Long-tailed and Rhesus macaques thrive in urban, suburban, and agricultural landscapes. In these areas, they rely heavily on anthropogenic food sources, such as discarded food from trash bins, direct provisioning by humans, and raiding agricultural crops.
Close proximity to human settlements often leads to human-macaque conflict, as their foraging translates into crop raiding and scavenging in residential areas. The availability of human-derived resources can lead to higher population densities and altered behavior, such as a reduced home range size. In many Asian cities, macaques are now habituated to human presence and exhibit behaviors that involve reading human actions to predict food availability.