Monkeys, highly social and vocal creatures, produce a diverse array of sounds that serve as sophisticated communication tools. These vocalizations convey specific information about their environment, social interactions, and potential dangers. Understanding these sounds offers a glimpse into the intricate world of primate communication.
A Symphony of Sounds: Types of Monkey Vocalizations
Monkey vocalizations can be broadly categorized into several types, each with distinct acoustic properties and contexts.
Alarm Calls
Alarm calls are a prominent example, serving to alert group members to threats. Vervet monkeys, for instance, produce acoustically distinct calls for different predators, such as sharp barks for leopards, short chirps for eagles, and “chutter” sounds for snakes. Similarly, Diana monkeys use loud, distinct alarm calls for leopards and eagles, which can travel over long distances. Campbell’s monkeys also exhibit specific calls, with a “krak” signaling a leopard and a “hok” for an eagle.
Contact Calls
Contact calls help maintain group cohesion and allow individuals to keep track of each other. These are often short exclamations, less conspicuous than alarm calls, and can vary between individuals. Chacma baboons use contact calls for identification and to signal their location to other group members, particularly mothers to their offspring. Pygmy marmosets have developed a vocal system with two acoustically distinct contact calls used for individual identification within their population.
Territorial Calls
Territorial calls are loud and carry far, used to mark a group’s boundaries or to signal presence to rival groups. Male Diana monkeys, for example, produce loud calls that serve in male-male competition and resource defense. Blue monkeys also use a loud, low-frequency “boom” call, often associated with asserting presence.
Social Calls
Social calls encompass a wide range of vocalizations used during daily interactions within a group. These include grunts, coos, chirps, and whimpers that facilitate activities like grooming, playing, or reconciling after conflicts.
The Meaning Behind the Calls
The meaning conveyed by monkey vocalizations is deeply intertwined with context and the specific information encoded within the call’s structure. Alarm calls are particularly illustrative, as their specific acoustic properties denote the type of predator and elicit precise, adaptive responses. Vervet monkeys, upon hearing a leopard alarm, will climb trees, while an eagle alarm prompts them to look skyward or seek cover in bushes. A snake alarm, in contrast, causes them to stand bipedally and scan the ground.
The complexity extends to call combinations; for example, Campbell’s monkeys can modify the urgency or specificity of their alarm calls by adding suffixes or combining different call types. A “boom-boom-krak” sequence might signify a distant leopard, prompting vigilance rather than immediate escape. Titi monkeys use “A-calls” for aerial predators and “B-calls” for terrestrial dangers, even combining them in sequences to convey information about the predator’s location, such as a terrestrial predator in the canopy. These examples show how monkeys interpret calls as representing external objects or events.
The “boom” call in blue monkeys, for example, has been observed to attract mates and deter rival males during breeding season.
Beyond Vocalizations: Other Monkey Sounds
Monkey communication extends beyond vocal cord-produced sounds to include audible actions involving their bodies or the environment. These non-vocal sounds play an important role in conveying messages, particularly in close-range interactions or displays.
One prominent example is chest beating, notably performed by gorillas. This powerful drumming sound, generated by striking their chest, can be heard over a kilometer away and serves to attract mates, assert dominance, and intimidate rival males.
Branch shaking is another non-vocal sound used by several monkey species. Capuchin monkeys, for instance, shake branches to demonstrate their strength, express annoyance, or deter potential predators. Barbary macaques also engage in branch shaking, often as a form of intra-group signaling. This action creates an audible rustling or cracking sound, drawing attention and conveying a message without a specific vocalization.
Some primates also utilize leaves to create sounds for communication. Chimpanzees, for example, have been observed tearing or rattling leaves, sometimes to flirt or engage in social interactions. These leaf-modifying gestures can vary in style between different chimpanzee communities, forming gestural dialects.