Age- and dominance-related variation in feeding time among free-ranging female rhesus monkeys

Observations were made on the feeding behavior of 34 lactating rhesus females (Macaca mulatta) at Tughlaqabad, India. Consistent interindividual differences in feeding times were found and two sources of this variation were identified. Time spent feeding was found to decline with female age; rhesus mothers 4-6 years old spent over 40% more time feeding than did females 11-15 years of age. When the animals were divided into high- and low-status groups, dominance was also found to relate to individual feeding times; high-status females spent more time feeding that did low-status females, but this difference was evident only when the effect of female age was held constant. The age effect is probably an expression of age-related variation in nutritional requirements due to growth in the youngest subject and, perhaps, a declining basal metabolic rate in the oldest. We speculate that the comparatively weak dominance effect is due less to the aggressive interruption of feeding bouts than it is to a presumed greater vigilance on the part of subordinant mothers in monitoring their infants' whereabouts.