Deceptive Animal Behavior: A Case Study in Alarm Calling
Vervet Monkeys (Cercopithecus aethiops) and Deceptive Alarm Calling
Vervet monkeys have many predators, among them leopards, eagles, baboons, and pythons. While predation is their biggest threat, their competitive interactions for resources are governed by a strict linear hierarchy. The ranks among adult females remain relatively stable over time, while the males have an unstable hierarchy and frequent turnover based on age and fighting ability. Female vervet monkeys stay with their natal groups for life; males, however, move to a new group upon reaching sexual maturity. In Kenya they live in a very open habitat, and their diet consists mainly of vegetation.
Q: Why might alarm calling be used in vervet monkeys?
Alarm calling is an essential aspect of vervet monkey communication. Because they live in an open habitat with many predators, they are at high risk of being attacked while foraging for vegetation. Thus, if a vervet is scanning the area and spots a predator, alarm calling can potentially benefit those around them and provide adequate time for escape.
Q: How do you think deception may be used in alarm calling?
Deceptively alarm calling can offer advantages to the caller. Because vervet monkeys are intelligent primates that can remember past social encounters (in which one monkey may have behaved altruistically), they deceive others for many reasons. To make use of deception in alarm calling, some monkeys withheld their alarm calls upon seeing a predator.
Q: Which monkeys do you think would be most likely to withhold their calls?
Deceptively alarm calling can offer advantages to the caller. Because vervet monkeys are intelligent primates that can remember past social encounters (in which one monkey may have behaved altruistically), they deceive others for many reasons. To make use of deception in alarm calling, some monkeys withheld their alarm calls upon seeing a predator.
As the percentage of females dominated increases, so too does the percentage of first alarm calls in the 1983 study. The closed circles represent females with close kin and the open circles represent females without close kin. This data indicates that in female vervets, the higher ranks are less likely to withhold the alarm call. Results from male vervet surveys were too scattered to represent significant data.
Q: What might be another factor in withholding alarm calls?
Presence of kin did slightly affect the alarm call frequency in vervets. The study shows that those scanning who had kin nearby were more likely to call. Those without kin nearby were more likely to withhold the information. In a captive study on males, they were more likely to deceive another male by withholding the call than a female.
Q: How did selectively deceiving by withholding alarm calls evolve?
Since vervets were less likely to deceive in the presence of kin, kin selection may be a factor in the evolution of this type of deception. In addition, the deception by males of other males (while the increased frequency of alarm-calling in the presence of a female) makes sense because it allows the male to get rid of his competitor and secure a potential mate. Evidence suggests that males also may gain higher ranks through their alliances with female; thus, they benefit from protecting females rather than males.
Q: Why, however, would high-rank females be less likely to deceive than those of lower rank?
High-ranking females hold access to the best resources, such as food and safe sleeping areas. They have much more to lose by deceiving and have a significant advantage in maintaining the group’s cohesion and stability since they can retain their rank, status and access to resources. It is also possible for turnover of the hierarchy to occur as a result of invasion by other vervet monkey groups; thus, the high-rank females benefit themselves by calling against not only predators but other vervets. Conversely, low-rank females have a significant gain by withholding their call: the death of a higher-rank individual would allow them to move up in the hierarchy by disrupting the status quo.
This kind of deception indicates that vervet monkeys understand the distinct identities of others, their relatedness, and the future benefits of protecting or not protecting them through alarm calling. For this reason, deception has effectively evolved in many non-human primates, as well as humans and other animals.
This case study was adopted from an experiment performed by Cheney and Seyfarth. Full citation: Cheney, D. and R. Seyfarth. 1985. Vervet Monkey Alarm Calls: Manipulation through Shared Information? Behaviour (94) 1: 150-166.
To read more on deceptive behavior in primates, click HERE.
This website was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2009. Please send any comments, questions, or suggestions regarding this website to Shawna Foley or Professor Verna Case.
Last updated May 1, 2009.
Image credits: All images from Wikimedia - Fanny Schertzer; DrKjaergaard; Whit Welles; Carlos Vermeersch Santana
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