Metabolic strategies in wild male Barbary macaques: evidence from faecal measurement of thyroid hormone

Selection is expected to favour the evolution of flexible metabolic strategies, in response to environmental conditions. Here, we use a non-invasive index of basal metabolic rate (BMR), faecal thyroid hormone (T3) levels, to explore metabolic flexibility in a wild mammal inhabiting a highly seasonal, challenging environment. T3 levels of adult male Barbary macaques in the Atlas Mountains, Morocco, varied markedly over the year; temporal patterns of variation differed between a wild-feeding and a provisioned group. Overall, T3 levels were related to temperature, foraging time (linked to food availability) and intensity of mating activity, and were higher in the provisioned than in the wild-feeding group. In both groups, T3 levels began to increase markedly one month before the start of the mating season, peaking four to six weeks into this period, and at a higher level in the wild-feeding group. Our results suggest that while both groups demonstrate marked metabolic flexibility, responding similarly to ecological and social challenges, such flexibility is affected by food availability. This study provides new insights into the way Barbary macaques respond to the multiple demands of their environment.