More Than a Scream: How Vervet Monkeys Use Specific Calls to Warn of Leopards, Eagles, and Snakes

When we think of animal sounds, we often imagine simple expressions of emotion—a bark of aggression, a purr of contentment, or a cry of fear. But in the savannas of eastern Africa, a small primate challenges this notion entirely. The vervet monkey has a communication system so specific and nuanced that it forces us to reconsider the boundaries between animal communication and human language. They don't just scream 'danger!'; they specify precisely what kind of danger is approaching.

A Symphony of Warning

Imagine you are a vervet monkey foraging on the ground. Suddenly, one of your troop lets out a loud, barking call. Instantly, without even seeing the threat, you and everyone around you scramble for the safety of the nearest tree. The bark was the signal for a leopard, a terrestrial predator best escaped by climbing. Now, picture a different scenario. A monkey lookout emits a short, double-syllable cough. This time, the troop doesn't climb. Instead, they look up towards the sky and dive for the cover of dense bushes. This was the alarm for a martial eagle, a threat from above. And if the call is a quiet, chuttering sound, the monkeys stand up on their hind legs and scan the grass around them, searching for the slithering danger of a snake.

These three distinct calls—the leopard 'bark,' the eagle 'cough,' and the snake 'chutter'—each trigger a unique and appropriate defensive maneuver. The reaction is immediate and specific to the information conveyed by the call, demonstrating a remarkable level of cognitive complexity.

More Than Just Emotion: The Dawn of Animal Semantics

This discovery was groundbreaking because it provided some of the first strong evidence for 'semantic communication' in a non-human species. Semantics is the concept of words or symbols having specific meanings. In this case, the vervets' calls aren't just involuntary shrieks of terror; they are functional signals that refer to specific things in their environment. Researchers Dorothy Cheney and Robert Seyfarth, who pioneered this research, confirmed this with elegant playback experiments.

What these experiments showed is that these calls are not just emotional cries. They carry information. A sound that refers to an object in the outside world.

By hiding speakers and playing recorded alarm calls to unsuspecting monkeys, Cheney and Seyfarth proved that the sounds alone were enough to elicit the correct defensive response. A recorded leopard bark sent them up trees, even when no leopard was present. This confirmed the calls themselves carried the specific meaning, much like our words for 'leopard,' 'eagle,' or 'snake' conjure a specific image and meaning in our minds.

Pioneering Research in the Wild

The work of Cheney and Seyfarth in Kenya's Amboseli National Park during the late 1970s and 1980s fundamentally changed the field of animal behavior. Their use of playback experiments in the animals' natural habitat was a novel approach that allowed them to decode these complex vocalizations. Their research showed that infant vervets seem to learn the correct use of these calls through social interaction, initially over-generalizing (for example, calling 'eagle' for any bird) and gradually refining their calls with age and experience. This suggests a component of social learning, another fascinating parallel to human language acquisition. The vervet monkey's alarm system remains a classic example of the sophistication hidden within the animal kingdom, reminding us that communication is a rich and varied tapestry woven throughout the natural world.

Sources

• NOVA | The Language of the Vervet Monkey
• How Monkeys See the World - University of Chicago Press
• History of the Warder Allee Best Student Paper Award - Animal Behavior Society