These generalizations are drawn primarily from our research on the rhesus macaque. We selected this species of primate because it is one of the most frequently used research subjects in laboratories around the world. Enrichment efforts without a capability for documenting and assessing any resultant psychological effects may not be worth the cost and contribute little to scientific knowledge. From these data, we established the vocal repertoire and associated behavior of the rhesus under natural conditions which serves as the normative base needed to interpret vocal behavior recorded under captive conditions. Although our research is far from complete, the data already indicate that this approach will become fruitful.
Vocal patterns do appear to vary with housing and treatment conditions.
The expression of emotion is there in the calls, in captivity as it is in the field. The difference is that, in captivity, an emotional state may be induced by human-imposed conditions, which may or may not be desirable. At least we now have a way of examining the question. Animal vocalizations appear to express pretty much the same things under captive and natural conditions. To the extent that this is true, vocal records provide an objective, real-time basis for monitoring emotional variation in captive animals.