Diana Monkey

Diana monkeys produce distinct alarm calls for different predator types—a vocal system that parallels meerkat alarm calling but evolved independently in the African forest canopy. Leopard alarms differ acoustically from eagle alarms, and group members respond appropriately: leopard calls trigger climbing higher, eagle calls trigger descent and freezing. This semantic alarm system demonstrates that referential communication evolves repeatedly when predation pressure is high.

The call-response specificity proves semantic content. When researchers played back leopard calls, monkeys looked down and climbed higher. When they played eagle calls, monkeys looked up and descended. The response isn't to 'danger generally' but to specific threat information encoded in the call. Playback experiments with artificially modified calls showed that acoustic features—not caller identity or context—determine response.

Cross-species communication extends the information network. Diana monkeys respond appropriately to Campbell's monkey alarm calls and even to hornbill alarm calls. This eavesdropping creates a multi-species early warning system. Diana monkeys don't just produce semantic signals—they extract semantic meaning from other species' communications.

False alarms exist but are rare. Some individuals give predator-specific calls when no predator is present, potentially to distract competitors from food. But the low false alarm rate suggests receivers track sender reliability. Frequent false-alarming would degrade the system's value.

For organizations, Diana monkeys demonstrate that specific threat categorization beats generic warnings. 'Danger' doesn't tell you what to do; 'leopard' does. Internal communication systems that specify threat types enable targeted responses.