Acoustic variation of spider monkey (Ateles geoffroyi) contact calls is related to caller isolation and affects listeners’ responses

Abstract

Group living animals produce vocalizations denominated “contact calls” to maintain contact with out-of-sight group members. These calls have been shown to vary with caller identity and distance to potential listeners. However, it is not clear whether the acoustic variation of contact calls is related to caller social isolation (e.g., inside or outside a subgroup) and listeners’ responses that can be helpful to maintain contact. Here, we addressed these questions in spider monkeys ( Ateles geoffroyi ), a Neotropical primate that exchanges contact calls denominated “whinnies”, which show graded variation related to caller immediate behavior and distance between callers. Using 566 whinnies produced by 35 free-ranging adult spider monkeys recorded at ≤ 20 m from microphones, we first analyzed whether the acoustic variation of spontaneous whinnies (i.e., whinnies that are not responses to previous whinnies) is related to caller social isolation or whether acoustic variation is related to the likelihood of eliciting a response whinny from another individual. Secondly, we assessed whether listeners’ responses (i.e., time to respond vocally, acoustic characteristics of response whinnies, orienting behaviors) were related to the acoustic variation of previous whinnies. Our study revealed that callers that were outside a subgroup produced whinnies with a lower fundamental frequency (F0), which travels longer distances, and increases the likelihood of producing a response whinny. Moreover, listeners (i.e., responders) responded faster to lower F0 whinnies. However, the acoustic variation (i.e., F0 variation) in response whinnies was better explained by the separation distance between callers, than by the acoustic variation of the previous whinny. Overall, our results suggest that whinny variation facilitates vocal contact to callers that are outside a subgroup, and that context and whinny variation affect listeners’ responses.

Born to sing! Song development in a singing primate

“…Primate vocal communication includes some very diverse acoustic outputs, ranging from low-frequency contact calls (e.g., spider monkeys— Ordóñez-Gómez et al. 2019 ) to elaborate vocal displays like songs (e.g.…”

Flexible use of contact calls in a species with high fission–fusion dynamics

“…They could also be varying other aspects of their calls depending on the social context. For example, there is evidence that they are able to modify their calls as a function of the distance between callers and recipients, as individuals emitted and respond with low frequency whinnies when callers are outside a subgroup (separated by long distances) to facilitate vocal contact [33].…”

“…Ordóñez-Gómez et al . [33] showed that individuals even lower the fundamental frequency of whinnies to facilitate communication and to maintain contact with distant individuals (those traveling outside their subgroup). Social cohesion is also supported by Briseño-Jaramillo et al .…”

“…Whinnies are loud enough to be audible by any member of a given subgroup and beyond [30]. Ordóñez-Gómez et al [33] showed that individuals even lower the fundamental frequency of whinnies to facilitate communication and to maintain contact with distant individuals (those traveling outside their subgroup). Social cohesion is also supported by Briseño-Jaramillo et al [34]'s study, which showed that call-matching between two individuals is higher between preferred grooming partners, in line with Dunbar's 'grooming-at-distance' hypothesis [35].…”

Flexible use of contact calls in a species with high fission-fusion dynamics

“…Whinnies are loud enough to be audible by any member of a given subgroup and beyond [30]. Ordóñez-Gómez et al [33] showed that individuals even lower the fundamental frequency of whinnies to facilitate communication and to maintain contact with distant individuals (those traveling outside their subgroup). Social cohesion is also supported by Briseño-Jaramillo et al [34] showing that call-matching between two individuals is higher between preferred grooming partners, in line with the Dunbar's "grooming-at-distance" hypothesis [35].…”