Abstract # 4476:

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N. Righini, R. Martinez-Mota and P. A. Garber
Department of Anthropology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
     Primates living in tropical deciduous forests may face periods of food shortage and/or dietary shifts due to seasonal fluctuations in resource availability. To investigate whether black howler monkeys (Alouatta pigra) experience seasonal nutritional stress, we studied two groups living in a semi-deciduous forest in Campeche, Mexico during 15 months (1300 observation hours). We conducted full-day focal follows (n=116) of one individual/day to record all feeding activities, including feeding rates, time spent feeding, and total amount (grams) of food ingested. We carried out nutritional analyses of foods collected from feeding trees and calculated the daily energy intake (kilojoules/metabolic body mass) of focal individuals, summing the energetic contributions from available protein, ether extract, and non-structural carbohydrates. Fecal glucocorticoids (fGC) of focal animals were used as an indicator of energetic stress. Mean energy intake did not vary significantly by month, but showed a positive relationship with time spent feeding (R2=0.42, p<0.001). fGC fluctuated greatly within and among individuals over time, and showed a tendency to be negatively correlated with feeding time and energy intake. However, the highest mean fGC peak, recorded at the onset of the rainy season, did not correspond to lower energy intake or lower feeding time, but only to a decrease in young leaf availability compared to the previous two months. Additional relationships between diet, nutrition, ecological variables, and temporal variation in fGC are discussed.