Social animals use various communication strategies to form and maintain relationships with other individuals. Often, it can be beneficial for animals to recognize familiar versus unfamiliar animals when communicating over long distances. That is because correctly identifying familiar individuals may decrease the need to participate in costly territorial behaviors. Among these, primates display a wide range of social groupings and many use vocal signals to communicate social information. For example, titi monkeys are a group of south American monkeys that form strong attachments between paired males and females and maintain a territory separate from other animals. Adult titi monkeys (Plecturocebus cupreus) use loud vocalizations, called duets. During these duets, the male and female alternate vocal components (different note types), to communicate over long distances. Titi monkeys are also very vocal as infants; the babies use trill vocalizations to communicate their needs to their parents. 

While adult and infant titi monkeys use vocalizations that are specific to their species and their age class (adults duet and infants trill) and there is a wide range of variability in what these vocalizations sound like. Researchers at UC Davis predicted that this variation comes from individual calls between each titi monkey, potentially allowing them to identify the difference between neighbors and strangers. To test this idea, the authors recorded the duet vocalizations of 30 adult and the trill vocalizations of 30 infant titi monkeys. They characterized each call based upon its frequency and temporal features. Individuals were then classified using a method that attempts to match a monkey’s call with the correct individual. 

The authors found that adults were identifiable with an 83% accuracy, while infants were identified with a 48% accuracy. The difference seen in these two ages classes likely emerges due to the different functions of these two call types. 

More broadly, this study provides the first evidence that titi monkeys have their own individualized voices. Future studies will be used to determine what information the titi monkeys can glean from these calls by playing recordings to the monkeys and assessing their behavior. Stay tuned for the results of those ongoing projects. 

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For more information:

Lau, A. R (*)., Clink, D. J., & Bales, K. L (*). (2020). Individuality in the vocalizations of infant and adult coppery titi monkeys (Plecturocebus cupreus). American Journal of Primatology, e23134.

*Stars denote authors currently with the UC Davis Animal Behavior Graduate Group.

Cover Photo Source: Alexander Baxter