This work presents new data from 48 maned sloths Bradypus torquatus captured between November 2002 and November 2003 in three regions of the Atlantic forest where the largest remnant populations of this species are found. Data from another long-term study, carried out from 1994 to 1996 and from 1999 to the present (n=14), were also used, making a total sample of 62 sloths. Average adult body weight is 6594±236 g and average head-body length is 66.5±0.8 cm (n=35), indicating that Bradypus torquatus is the heaviest of all four Bradypus species. Individuals from lower-montane forests (600–1000 m a.s.l.) are significantly larger (head–body length; t-test; P=0.001) than individuals from the lowlands (<350 m a.s.l.), suggesting altitudinal differentiation between populations. Sexual dimorphism, here reported for the first time, was found in body length (females are significantly larger than males) and in other external characters, such as mane size and form (darker and larger in males), and size and shape of the external genitalia. Most differences between sexes are, however, only discernible in reproductively active individuals. Breeding is slightly seasonal; minimum observed interbirth interval was 1 year and litter size was always one. Infants stayed with their mothers until 8–11 months old; started feeding on solid food as early as 2 weeks old but continued suckling until c. 4 months of age. Age of sexual maturity was estimated at 2–3 years and the oldest captured maned sloth was a healthy male who was at least 12 years of age. Overall, results indicated that maned sloths are similar in these aspects to congeneric species. Information presented here significantly improves the current knowledge on this endangered sloth species and is useful for the proper planning and implementation of in situ conservation strategies such as translocations and reintroductions.

Three maned sloths were observed for a total of 680 h throughout 14 months in an Atlantic forest reserve of south-eastern Brazil. The study animals were located in the forest, monthly by radio-telemetry, and data on daily activity budgets were collected recording the actual time they spent in major activities. Individual home ranges were very small (0.5–6 ha, depending on the method used) and the sloths travelled an average of only 24 m during the 24 h period. A comparison between day- and night-range lengths suggests that maned sloths ranged more during daytime (17 m) than at night (5 m), indicating a predominantly diurnal period of activity. They rested, on average, for 74% of daytime, but a substantial variation was found between individuals (range 60–80%). Although a lack of synchrony was observed in activity pattern between study animals monitored simultaneously, all three sloths tended to start feeding and moving at the same time of the day (07:00–08:00), and the time that elapsed between the start of these activities on consecutive days was about 24 h, indicating a circadian rhythm of activity for the species. This finding contradicts previous studies on congeneric sloths, in which suggestions that Bradypus does not show cyclic patterns of activity were based on qualitative rather than quantitative data. Given the species' highly folivorous diet and the characteristic low basal rate of metabolism in this genus, the rather high levels of activity and the predominantly diurnal period of activity observed for maned sloths are probably related to the lower ambient temperatures found in the Atlantic forest when compared to other more equatorial localities of the Neotropics. Further studies with additional sloths are necessary, however, to ascertain the validity of this conclusion.

The diet of maned sloths was studied throughout 14 months in an Atlantic forest reserve of south-eastern Brazil. Three adult sloths were observed for a total of 680 h and located monthly by radio-telemetry. Data were collected on diet, recording the actual time the sloths spent eating plant species. Overall, the diet was composed of 99% leaves, with young leaves (68%) preferred to mature ones (7%) throughout the year. A higher proportion of tree leaves (83%) than liana leaves (16%) were included in the diet. When analysed together, the diet of the three animals included a total of 21 plant species (16 tree and 5 liana), but each individual made up its diet with an even smaller number of species (7–12) and with a particular subset of the local flora. This is a very small portion of the total number of tree and liana species available to the sloths; furthermore, the top species consumed were present at very low population densities in the forest. Thus, B. torquatus, like other congeneric species studied elsewhere in the Neotropics, is a strictly arboreal folivore with a highly selective diet, probably resulting from evolving physiological adaptations to cope with a smaller range of plant secondary compounds. This is possible for the species of this genus through a combination of low basal rates of metabolism, which enable the sloths to survive on an energy-poor diet, and a very long passage time of digesta, which, in turn, aids the digestion of a fibre-rich diet while possibly contributing to the degradation of secondary compounds.