Eating Smart When Time Is Short: Stable Performance Despite Reduced Feeding Time During Reproduction in Mantled Howlers

Reproduction imposes substantial energetic costs on female mammals, yet how females that show reduced overall energy expenditure adjust foraging to meet these demands remains incompletely understood. We examined two dimensions of behavioral response in female mantled howler monkeys (Alouatta palliata): feeding time (how much of the day, and how often, females feed) and foraging performance (the rate of dry matter intake when feeding occurs). We tested three hypotheses: (H1) females maintain stable feeding time and stable intake rate across reproductive states; (H2) females maintain stable feeding time but elevate intake rate during gestation and lactation; (H3) females reduce feeding time and do not elevate intake rate. Using 3,765 focal observations from 11 females across ten years, we classified reproductive state as cycling, gestating, early, mid, or late lactation, or concurrent gestation with lactation. Feeding time declined during reproduction: early lactating, mid-lactating, and concurrent females allocated approximately 15, 16, and 29 fewer minutes per day to feeding than cycling females, and the probability of feeding during a focal sample fell by 6.1 and 7.4 percentage points in early and mid lactation. Foraging performance did not vary: when females fed, intake rate, total intake, and diet composition were comparable across states. These results support H3. Combined with parallel evidence from this population that lactating females increase resting rather than feeding time and show no elevation of dry matter intake during lactation, our findings suggest that female mantled howlers meet reproductive costs primarily by drawing on capital reserves rather than through behavioral compensation.