Common marmosets use high, whistle-like phee calls to maintain contact when foliage or distance blocks a clear view. Researchers recorded spontaneous phee-call dialogues between pairs and analyzed whether the sound varied only with the caller or also with the intended receiver. The calls contained acoustic patterns that let the team identify which individual was being addressed.

Playback added the receiving side of the evidence. Marmosets responded more consistently and correctly when a call was specifically directed toward them. Family members also converged on similar acoustic features when labeling another monkey, suggesting that at least part of the pattern is socially learned within a group rather than fixed entirely at birth.

The authors describe these signals as vocal labels, placing marmosets alongside a small set of animals known to direct individually distinctive calls at companions. “Name-like” is safer than claiming a human naming system. The study did not show written symbols, words combined into grammar, or each monkey inventing a permanent personal name independent of context. It showed a practical social address: the form of a familiar contact call shifts according to whom the caller is trying to reach, and the intended listener can hear the difference.