Acoustic and behavioral analyses of gecker distress vocalizations in young rhesus macaques (Macaca mulatta)
Loud, pulsed gecker calls have long been known as one of the most common distress vocalizations produced by young rhesus macaques, but have not been systematically investigated. We therefore examined the rates, acoustics, and behavioral contexts associated with geckering, based on audio-recording and focal-animal observations conducted over 4 years at the California National Primate Research Center. The sample analyzed came from 14 young rhesus macaques, with 74 recorded gecker bouts and 556 total pulses. Callers ranged from 1 to 41 months, who in their first year showed most geckering in months 0-2 (26%) and 2-4 (35%). Females geckered longer and at higher rates than males, as well as showing acoustic differences likely to reflect greater vocal effort (e.g., more doubled and tripled pulses, greater noisiness, and higher first frequency peaks). Geckers were associated with 22 differentiable behavioral contexts, typically occurring when with the mother but without obvious antecedents (31.1%), and when the mother broke physical contact with the youngster (13.5%). The most frequent postcedent context of geckering was that most offspring gained the mother's attention and/or renewed proximity (49%). In combination, the outcomes suggest that geckers primarily function to draw listener attention, and are used by youngsters to elicit maternal response.