Hierarchy splits vocal signaling during cooperative action in marmosets
In a small but tightly observed study of common marmoset dyads, cooperation did not produce a single shared vocal pattern. It split cleanly along social rank. Dominant animals produced t-peeps, while subordinate animals produced chirps, and each call carried a different relationship to the state of the joint task. The animals were learning a mutual cooperation paradigm that required coordinated lever pulls for reward, making the setting a direct test of how communication is organized when two partners must succeed together rather than act alone.
The result is more than a catalog of primate calls. It points to a division of labor in communication itself. Dominants signaled most strongly when cooperation broke down, while subordinates signaled during successful joint action. In that sense, the vocal exchange tracked not just who was speaking, but who was leading, who was following, and whether the pair was moving toward reward or losing synchrony.
Failure and success were encoded by different voices
Dominant animals emitted more t-peeps after failed cooperative pulls. Those calls peaked when cooperative bouts fell apart and then declined after the dyads learned the task. Subordinates followed the opposite pattern. Their chirps came after successful pulls, accumulated during sustained cooperation, and remained present even after learning stabilized the task structure.
The asymmetry is striking because it links vocal output to the immediate status of interaction. A failed pull is not just a mechanical miss; it is a social event that signals misalignment between partners. In a coordinated task, breakdowns can expose hesitation, timing mismatch, or uncertainty about role assignment. Dominant t-peeps appearing at those moments fit a function as a signal of failed coordination or task disruption. By contrast, subordinate chirps emerging after success fit a reinforcing role, marking achievement and perhaps helping maintain the rhythm of continued cooperation.
A single cooperative bout could therefore contain two different social messages, separated by rank and by outcome.
Task role shaped when each animal called
The vocal division did not stop at hierarchy. Each call also aligned with the caller’s role in the task. Dominant animals t-peeped more in sessions they led, while subordinates chirped mainly after cooperations they initiated. Those associations became sharper with learning, suggesting that experience refined the link between action ownership and vocal expression.
This matters because leadership in cooperation is not only behavioral; it is communicative. An animal that initiates a successful cooperative sequence may be marking agency, while a partner that follows may be registering the social and temporal structure of the exchange. Vocalizations then act as readouts of who controlled the tempo of cooperation and how the pair distributed responsibility across the task. Over time, repeated exposure appears to tighten that mapping, so the calls become more tightly tied to the animal’s position in the interaction.
Social rank and cooperation appear to recruit different signaling functions
The study suggests that vocal communication in marmoset cooperation is organized by at least three variables at once: social rank, task role, and the phase of the cooperative sequence. Rank determined which signal an animal used. Task role influenced when that signal appeared. The momentary state of cooperation determined whether calls clustered around failure or success.
That architecture fits well with what is known about primate social behavior, where vocal signals often carry layered meaning rather than a single fixed message. In a pairwise task, the partner relationship is especially transparent. Two animals must coordinate tightly enough to achieve a shared reward, and any mismatch becomes immediately visible in the behavioral record. Vocalizations offer a window into that interaction, revealing how the social hierarchy is translated into timing, and how timing is translated into sound.
What the dyads reveal about joint action
Because the task required coordinated lever pulls, the animals were not merely vocalizing in the presence of a partner. They were communicating inside an ongoing joint action system. That distinction gives the findings their force. Cooperation creates a moving target: each success changes the next opportunity, and each failure changes the social context of the next attempt. In that setting, a dominant’s t-peep after a missed pull may serve as a marker of disruption, while a subordinate’s chirp after success may help sustain a cooperative sequence that is already working.
The complementarity of the two calls is especially informative. One signal tracks breakdown, the other tracks success. One is tied to dominant animals, the other to subordinates. One drops off as learning reduces conflict or uncertainty, while the other persists once the pair has acquired the task. Together, they suggest that cooperation does not erase hierarchy; it organizes it into a communicative system with different roles assigned to different animals.
A preprint that opens more questions than it closes
As a preprint, the study has not yet passed peer review, and the dataset described here is small, centered on three dyads. Even so, the observations are coherent enough to raise a larger question about primate communication: whether vocal signals during cooperation are best understood as general expressions of arousal or as role-specific tools for managing shared action. The present findings favor the second view.
The next step will be to test whether the same pattern appears in larger groups, under different cooperative demands, or in settings where dominance relationships are less fixed. It will also be important to determine whether the calls influence partner behavior in real time, rather than simply reflecting it. For now, the study offers a detailed account of how vocal signaling in marmosets can divide along social and behavioral lines, with dominants marking failure and subordinates marking success in the middle of a cooperative exchange.