Marmosets, small New World primates, are remarkably vocal animals. They use a diverse array of sounds to navigate complex social lives and communicate over distances where visual cues are limited. Their vocalizations play a significant role in daily interactions and survival within dense rainforest habitats, maintaining group cohesion and responding to environmental challenges.
Types of Marmoset Vocalizations
Marmosets produce a variety of sounds, categorized into simple and compound calls based on acoustic characteristics. Simple calls are single, distinct vocalizations, while compound calls combine multiple simple calls into a sequence. A common simple call is the “phee,” a loud, high-frequency whistle.
The “trill” has a fluctuating frequency, and the “twitter” is a rapid series of elements quickly rising in frequency. Marmosets also produce “chirps,” which are quiet, rapid, regularly spaced notes where each element falls from high to low frequency.
Compound calls include the “trillphee,” which starts as a trill and ends as a phee. Researchers analyze the acoustic morphology of these vocalizations by measuring various acoustic features.
The Purpose of Their Calls
Marmoset vocalizations serve a range of functions, facilitating social behaviors and interactions. The “phee” call primarily maintains social contact, especially when individuals are out of sight. These calls are also used in aggressive territorial encounters.
Trills are used for short-range contact between marmosets, often by bonded partners. Twitters, a long-distance call, are employed within a group and during interactions with other groups, indicating alertness or agitation. Chirps are quiet, within-group calls made in close social contact and friendly contexts, often heard when marmosets are near favored food.
Marmosets also produce calls like “ek,” “tsik,” and “chatter,” each linked to specific situations, such as the presence of a predator or an unfamiliar individual. “Phee” calls have been found to identify and address specific individuals, similar to how humans use names, reinforcing social bonds and group cohesion.
The Structure of Marmoset Communication
The structural organization of marmoset vocalizations reveals intricate sequencing rules. Marmoset “phee” calls exhibit consistent interval patterns between syllables, allowing for categorization into different grades based on the number of closely spaced syllables (e.g., single, 2-4 syllables). The ordering of sequential calls follows distinct probabilistic rules, favoring the repetition of the same-grade call or transitions between adjacent grades, while avoiding “skip-grade” transitions.
The duration of intervals between calls can depend on the direction of the transition between call types. Researchers have identified specific long-range sequencing rules, such as prominent “ABnA” call patterns in longer sequences, where the occurrence of these patterns decreases predictably with increasing “n.” These complex rules are observed both when marmosets call in isolation and during vocal turn-taking, where they alternate “phee” calls without overlapping.
Marmosets can combine multiple calls, sometimes up to eight or nine, and exhibit evidence of recombination, nestedness, and non-adjacent dependencies, suggesting a hierarchical structuring of their vocalizations. The contact calls, such as trills and phees, appear to be core combinatorial units within these sequences.
Learning Marmoset Sounds
Marmosets acquire their vocalizations through a developmental process that involves social learning and parental influence, demonstrating vocal plasticity. Unlike the assumption that non-human primate vocalizations are predetermined at birth and fully developed early, marmoset vocal development extends over a longer period. While some changes in call features are linked to physical maturation, the sequences and transitions between calls remain adaptable into adulthood.
Marmoset vocal behavior develops in stages that align with their motor and social development, similar to human infants. Early vocalizations, resembling baby cries and babbling, gradually mature into adult calls. Parental feedback plays a significant role in this transition; marmosets separated from their parents may continue to produce more immature, baby-like vocalizations into adulthood.
Adult marmosets can adaptively modify the spectrotemporal structure of their vocalizations in response to interfering sounds. They can make predictive and long-lasting spectral shifts in their calls after experiencing certain types of noise, demonstrating directional control over their vocalization spectrum and long-term vocal flexibility. This prolonged vocal plasticity in marmosets is considered an evolutionary precursor for vocal learning and speech in humans.