Activity budget, pattern and rhythm of maned sloths (Bradypus torquatus): Responses to variations in ambient temperature

Abstract

Three-toed sloths (Bradypus) are heterothermic, and ambient temperature may have a direct effect on their activity levels. Our goal was to describe the time budget, pattern and rhythm of activity of the maned sloth, Bradypus torquatus (Xenarthra: Bradypodidae), and to evaluate the effect of ambient temperature on its activity. We hypothesized that (1) sloth activity increases with ambient temperature, fluctuating with the circadian temperature cycle, and (2) sloths are more active in the diurnal period during colder seasons than warm seasons due to constraints or avoidance of the colder times within a 24-h cycle. Nine radio-collared individuals were followed in forest remnants in southern Bahia, Brazil from March 2003 to April 2014. Behavior data of 8 sloths were collected during the diurnal period by direct visualization (608h of record), and the activities of 4 sloths were recorded by an automated system during continuous hours (744h of record). The maned sloths exhibited low activity levels, resting 77% of a 24-h period. In general, they were cathemeral, although they were twice as active in the diurnal phase (active 32% of the time) compared with the nocturnal phase (15%). The ambient temperature had a significant positive effect on activity levels. The rhythm of activity was circadian and synchronized with the ambient temperature. No difference was detected in the diurnal activity between hotter and colder seasons, most likely reflecting the low fluctuations in climatic conditions of this tropical forest. The narrow relationship between the circadian activity pattern of maned sloths and the ambient temperature cycle highlights their poor thermoregulatory ability. The lower activity levels exhibited during colder times may represent a behavioral adaptation that reduces heat loss, enhances body temperature control and optimizes energetic benefits, a key feature for a species relying on a low energetic diet.