Individual differences in response to a stranger: Social impulsivity as a dimension of temperament in vervet monkeys (Cercopithecus aethiops sabaeus)

Social impulsivity in response to a stranger was assessed in male vervet mo nkeys (Cercopithecus aethiops sabaeus) using the Intruder Challenge Test. V ervets (N = 128, ages 3-18 years) were presented with an unfamiliar adult m ale at the periphery of the home enclosure. An index of impulsivity reflect ing variation in the tendency to rapidly approach, engage, and challenge th e intruder was derived from factor analysis of behavioral responses. Scale reliability (alpha = .84) and test-retest consistency (intraclass correlati on = .83) were high, indicating that this index reliably and efficiently me asures a stable aspect of temperament from impulsive to inhibited. Impulsiv ity scores peaked at age 4, when vervet males typically emigrate from the n atal group. The highest ranking males in each group were more likely to sco re in the moderate range, whereas lower ranking males were more likely to s core in the highest (impulsive) or lowest (inhibited) quartiles.