Gelada monkeys listen to the calls of rivals to scope out opponents

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Gelada males - monkeys that are related to baboons - listen to the loud calls of rivals to gain information about their strength. The monkeys use these calls to discern the strength of other males relative to them, and whether or not it's worth fighting them. Males who lead large harems of females engage in the loud calls to deter challenges from bachelor males, who compete with leader males to gain access to females.

Geladas, also known as 'bleeding heart baboons,' are a species of monkey found only in Ethiopia. They have a red patch of skin and their chest and neck - something that no other primate has.

Researchers based at the University of Michigan, Georgia State University and Princeton University have discovered that gelada males decide to escalate contests with opponents based on their condition relative to to the condition of their opponent.