Field Metabolic Rate, Water Flux, and Food Consumption in Three-Toed Sloths (Bradypus variegatus)

Abstract

Metabolic rates (CO2 production) and water fluxes were measured using doubly labeled water in free-living three-toed sloths ( Bradypus variegatus ) on Barro Colorado Island, Panama Canal Zone. Feeding rates were calculated from metabolic rates using natural tracer estimates of energy assimilation efficiency. Field metabolic rates averaged about 147 kj (kg day)−1 and did not differ significantly among nonre-productive females, lactating females, and males. This rate is only about 74% of the predicted mammalian basal metabolic rate, but is about 1.8 times the actual basal rate of these animals. Field water fluxes, ca. 38 ml h2O (kg day)−1, were also comparatively low and can be accounted for by dietary water input and metabolic water production alone. This indicates that sloths probably did not drink, even though rain fell during the study. The two lactating females allocated 5% and 11% of their water and assimilable energy intake, respectively, to producing milk for their offspring. We estimate that a 4-kg sloth consumes 60 g dry mass of food per day, and that the three-toed sloths on Barro Colorado Island eat 138 kg dry mass of food per ha per year. This is about 2% of the yearly leaf production.