The term “monkey” generally refers to the nearly 300 species of primates that are neither apes nor tarsiers, including both New World and Old World monkeys. Accurately counting the global population of any widespread wild animal is nearly impossible. Scientists rely on criteria like extensive geographic range, high population density, and adaptability to determine the most numerous species. The most common species must demonstrate an exceptional ability to thrive across diverse environments and in close proximity to human populations.
Identifying the Most Numerous Monkey Species
The most numerous monkey species in the world is the Rhesus Macaque (Macaca mulatta). This Old World monkey is considered the most widely distributed non-human primate, which contributes to its high population count. Although the exact global population is unknown, the species is officially listed by conservation bodies as being of “Least Concern.”
This designation reflects a robust and stable population across its native range. Unlike other widespread macaques, the Rhesus Macaque’s numbers are often increasing, sometimes leading to conflict with human communities. Its ability to maintain high population densities across multiple countries confirms its status as the most populous monkey species.
Drivers of Their Ecological Success
The Rhesus Macaque’s success stems from flexible biological and behavioral traits, allowing it to exploit a wide range of ecological niches. The species is a generalist omnivore, consuming fruits, seeds, roots, insects, and small vertebrates. This opportunistic feeding is invaluable for survival in varied environments.
This dietary flexibility allows them to thrive in human-dominated landscapes, incorporating agricultural crops, discarded human food, and refuse into their diet. The species also tolerates climatic extremes, surviving both scorching summer heat and winter temperatures below freezing.
Group dynamics further contribute to their success, as Rhesus Macaques live in large, multi-male, multi-female social units that can number in the hundreds. Females remain in their birth group, a structure called female philopatry. This maintains strong, stable, and cooperative matrilineal hierarchies that enhance the group’s survival and reproductive output.
Global Distribution and Habitat
The Rhesus Macaque possesses the largest native geographic distribution of any non-human primate, which correlates directly with its massive population size. Its range spans a vast area across Asia, covering 11 countries and a diverse array of terrestrial biomes.
The distribution begins in Afghanistan and Pakistan in the west and extends eastward through India, Nepal, Bangladesh, Myanmar, Thailand, Laos, and Vietnam, reaching the Pacific coast of China. The species occupies habitats ranging from arid grasslands and scrub forests to deciduous woodlands and mountainous regions up to 4,000 meters.
The macaque’s adaptability allows it to flourish in human-altered landscapes, including agricultural fields, suburban areas, and dense urban environments, particularly in northern India. Introduced populations also exist outside its native range, such as in the Florida wild and on research islands off the coast of Puerto Rico, further demonstrating its capacity to colonize new environments.