Heeding the Cry of a Stranger: Diana Monkey Alarm Calls and Familiarity

One of the greatest acts of cooperation a mammal can do is put their own life in jeopardy to warn others of coming danger. Different species encode different information in their alarm calls: elevation, urgency, and how the animal found the threat are all factors that have been shown to be encoded in primate alarm calls (Stephan & Zuberbühler, 2016). The Diana monkey encodes for the type of predator seen with distinct alarm calls for leopards, eagles, and general threats. Two researchers from the University of Neuchâtel in Switzerland set out to see if Diana monkey calls also encoded speaker identity using two Diana monkey populations, one in the Taï Forest in the Ivory Coast and one in the Tiwai Island in Sierra Leone (Stephan & Zuberbühler, 2016).

In this study, researchers played a recorded familiar or unfamiliar Diana monkey alarm call to monkeys in both habitats.  Researchers collected alarm calls from, and then tested alarm calls on, the 23 male Tiwai Diana monkeys and 20 male Taï Diana monkeys who were considered leaders of their respective mating groups.  A total of 4,910 responses to these calls were recorded, 3,002 of which were from Tiwai Island monkeys and 1,908 were from Taï Forest monkeys. The researchers then compared the calls to see if there was any difference between how the monkeys responded to leopard, eagle, or general alarm calls when the monkey was responding to familiar male calls from their own population or unfamiliar calls from the other population.

These results showed that the response rate in monkeys remained the same regardless of who sent the call but that latency, or time between hearing the call and sending out a response call, was longer in monkeys who heard the unfamiliar call, but only for particular predators. in the Taï monkeys, responses to both eagle and leopard alarm calls were slower.  Tiwai monkeys, who do not have leopards as a significant threat but do have eagles as a major predator, only responded slower to the eagle alarm call with unfamiliar callers, and responded to an eagle or general alarm call equally, regardless of speaker familiarity.

These results show that Diana monkeys do encode social familiarity in their responses but that consideration of social familiarity in making a response call is tied to what caused the initial call in the first place. When the threat was seen as extreme and specific, as it was in eagle and leopard calls in Taï monkeys and leopard calls in Tiwai monkeys, monkeys were slower but equally likely to eventually call when the speaker was unfamiliar. These behaviors imply that Diana monkeys can convey multiple factors into their alarm calls, namely predator type and social groupings, and that these behaviors are specific to their habitat and the specific predator risks in it. The results of this study expand what we previously thought primates were capable of communicating and lead to exciting implications for what future research in this field will bring!

Reference:

Stephan, C., & Zuberbühler, K. (2016). Social familiarity affects Diana monkey (Cercopithecus diana diana) alarm call responses in habitat-specific ways. Royal Society open science, 3(2), 150639. doi:10.1098/rsos.150639