Intricate Whinny

The immersion Internship at Pacific Primate Sanctuary (PPS) provides Interns with an opportunity to expand their knowledge of New World Primate species, both through hands-on experience as well as making use of educational resources. The monthly Talk Story- Special Topic encourages Interns to gain a more in depth understanding of each of the species here at PPS.  Following is a Special Topic written by Intern Clara

Intern Clara: Special Topic

When approaching Carlos and Montana’s Enclosure, you can hear them making a high-pitched vocalization called a whinny. It is one of the most common vocalizations we hear at the Sanctuary, and it is a friendly interaction. In the wild, a spider monkey can hear the call of another of its troop members as far as 900 feet away. 

The essence of the whinny can be explained by spider monkey behavioral ecology and ranging patterns. They feed mainly on ripe fruits, which are rare in the forest compared to other sources of food, such as leaves. Thus, spider monkeys have adapted to reduce food competition in the group and, in doing so, increase the likelihood of survival. To do so, they live in fission-fusion societies which means that troops split up during the day into subgroups. This process aims at reducing food competition between the different members by spreading far away from each other while foraging in the rainforest. To maintain their social cohesion and communication, they developed long-distance calls. The whinny is one of them. 

Changes in frequency within one whinny call allows the sharing of information, even if individuals are far away from each other. Indeed, the “abrupt changes in fundamental frequency” (Campbell, 2008) allow the call to be distinctive, even if the canopy acts as a noise buffer. It is also hypothesized that they can recognize each other based on the frequency, modulations, duration and number of elements of their call, in a similar way that humans can recognize each other by hearing voice alone. But what is the purpose and information carried out by a whinny? One hypothesis is that it is used to indicate food availability to other subgroups foraging for food. In a study on Ateles geoffroyi in Costa Rica, it was observed that spider monkeys were more likely to whinny if there was more food available in their food patch. The number of calls emitted also impacted the likelihood of other subgroups joining the food patch; the more calls emitted, the more likely other members were to join.  This is regularly observed at PPS, as Carlos and Montana both whinny frequently when they receive their breakfast bowls each morning, likely letting one another know that food is abundant. 

Another hypothesis is that the whinny maintains contact between individuals when they cannot see each other. A  different study on Ateles geoffroyi, in Mexico, showed that the receiver of the call was more likely to approach the emitter if they were close to each other socially (if they have a strong bond or know each other well). One possibility is that the call could solely communicate information about the emitter’s identity and that the receivers respond according to their mutual relationships.  At PPS, we can assess when Carlos and Montana gain comfort with a new caregiver, as they will start to whinny at their caregivers more frequently when they know them better.  This can help us determine when a new caregiver should start to feed Carlos and Montana, or hose their Enclosure. 

Contrary to alarm calls that generate direct actions from the recipient, there is a great variation in the response of other group members when hearing a whinny. In some cases, the recipient(s) of the call will whinny back or take a particular action. In others, there will be neither vocal nor physical response. This makes the whinny hard to interpret and to explain. Based on the analysis of the call itself, it is almost certain that the individuals have distinctive calls that are recognized by other troop members. This generates different responses based on the context and the relationship the receivers have to the emitter.

Reference cited

·       Campbell, J. Spider Monkey: Behavior, Ecology and Evolution of the Genus Ateles. Cambridge University Press, 2008.