Parturition in non-human primates: pain and auditory concealment.

Descriptions of parturition are reviewed for 88 individuals in 29 species of captive and wild non-human primates. Mild or severe discomfort, in the form of straining, stretching, arching, grimacing, writhing, shaking, doubling up, eye closure and restlessness is reported in 69 cases. Silence and utterance of moderate-level vocalizations are reported in 21 and 43 cases, respectively. The overall pattern indicates that parturition in non-human primates is characterized by a significant degree of pain and discomfort, while vocal responses to pain are generally subdued. We suggest that analgesia is the mechanism, and concealment of the parturient female the adaptive significance behind this blocking of vocal pain responses.