Wild monkeys use loud calls to assess the relative strength of rivals

June 21, 2017 by Jared Wadley

Gelada males—a close relative to baboons—pay attention to the loud calls of a rival to gain information about his relative fighting ability compared to themselves, a new study indicated.

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

They appear to do this by using the acoustic quality of the loud calls of their rivals—long-distance vocalizations that carry honest information about the fighting ability of the caller.

There has been much debate on specifically how animals make competitive decisions during contests. Game theoretical models predict that animals should assess an opponent's condition relative to their own condition prior to engaging in combat to avoid costly fights they are unlikely to win, a strategy known as mutual assessment.

Despite the benefits of such mutual comparisons ("I am stronger than him"), remarkably few studies have been able to reject much simpler assessment strategies such as self-assessment ("I am strong and should fight") and opponent-only assessment ("he is strong and so I should not fight").

Researchers say one approach for distinguishing these strategies is to use animal displays (rather than aggressive contests) to examine how animals make informed decisions about rivals.

"Particularly for quality signals that contain honest information on the condition of its bearer, signals used in animal displays offer an ideal situation for examining mutual assessment because they are low cost and allow for experimental manipulation," said Marcela Benítez, a postdoctoral research associate at Georgia State University and the study's lead author.

In geladas, harem-holding "leader" males engage in loud call displays to deter challenges from "bachelor" males, who must compete with leaders to gain reproductive access to females. Supporting a mutual assessment strategy, gelada males responded to loud calls of different quality (in both playback experiments as well as in natural observations) according to attributes of themselves and their opponent.

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Gelada Baboons Keep Sexual Infidelity Hush-Hush

Joseph Castro, LiveScience Contributor

Between secret rendezvous, deleted messages and outright lies, people will go to great lengths to cover up unfaithful acts. But it now seems we aren't unique in our deception — gelada baboons also actively try to hide their infidelity, new research suggests.

"This kind of deception is common in our society, but it is so difficult to prove that any other animal does it," said lead researcher Aliza le Roux, a behavioral ecologist at the University of the Free State in South Africa. "Here's some evidence that we aren't alone in the world in this, and there are evolutionary roots to our behavior."

CREDIT: Aliza le Roux 

Gelada baboons (Theropithecus gelada) live in small units, which consist of up to a dozen females, a few subordinate males and a dominant male, who holds exclusive reproductive rights to the females. Geladas live in an open grassland habitat and typically produce loud vocal calls during mating, so the dominant male should be able to easily detect any infidelity and stop it from happening. But previous research showed that follower males sire about 17 percent of a group's offspring.

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http://www.livescience.com/27046-gelada-baboons-hide-sexuainfidelity.html