Measuring temperament in rhesus macaques: consistency and change in emotionality over time.

This study of rhesus macaques (Macaca mulatta) investigated whether individual differences in emotionality, as measured by scratching frequencies, are stable over time and across seasons. Five adult females living in captive social groups were observed during two consecutive birth seasons and five females during the birth and the mating season. Scratching frequencies were higher during the birth than during the mating season, suggesting that the presence of infants was associated with elevated emotionality. Individual differences in scratching frequencies remained stable across two consecutive birth seasons, but there was no significant correlation between scratching frequencies in the birth and in the mating season. These findings suggest that, under certain circumstances, individual differences in emotionality are consistent over time and that scratching may be used as a non-invasive indicator of temperament.