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Individual study: Translocation of maned sloths Bradypus torquatus from degraded Atlantic forest fragments in Santa Teresa, Espírito Santo, Brazil

Published source details

Chiarello A.G, Chivers D.J., Bassi C., Amelia M., Maciel F., Moreira L.S. & Bazzalo M. (2004) A translocation experiment for the conservation of maned sloths, Bradypus torquatus (Xenarthra, Bradypodidae). Biological Conservation, 118, 421-430

Summary

The maned sloth Bradypus torquatus, is endemic to the Atlantic forest of eastern Brazil within the states of Bahia, Espírito Santo and Rio de Janeiro. It is an endangered species which has suffered local extinctions over much of its range due extensive habitat degradation and fragmentation. Maned sloths have great difficulty in travelling between forest fragments across open ground and individuals have been found 'stranded' in forest fragments around urban and agricultural areas where they are susceptible to hunting by humans, predation by domestic animals e.g. dogs, stress and starvation. Therefore, a maned sloth translocation experiment was undertaken as a conservation initiative for sloths stranded in forest fragments.

Translocations: The translocation programme commenced in 1994, with the capture of sloths stranded in forest fragments within or close to urban areas. The sloths were translocated to forest reserves in the municipality Santa Teresa, Espírito Santo. Five adult sloths were radio-collared and following release at one of two forest reserves, were monitored on a monthly basis for periods of 10 months to three years.

Santa Lucia Biological Station (SLBS): At SBLS, three sloths were released and monitored from December 1994 to May 1995. SLBS consists of 440 ha of protected land surrounded by an area of privately owned forest, totalling about 900 ha of forest overall. The vegetation is predominately primary forest.

Sao Lourenco Municipal Reserve (SLMR): Situated 9.9 km west of the SLBS, this site has similar primary forest. Monitoring was carried out from January 1999 to December 2002.

Sexing: Examinations were carried out of the translocated individuals (body measurements and weight were recorded). Due to males having internal testes, sexing is difficult. Two individuals released (one each in SLBS and SLMR) were determined to be females as one was bearing an infant when caught and the other was subsequently observed giving birth.

One individual released at SLBS could be sexed positively as a male due to external characters; a well developed black mane, longer external genitalia than adult females and a body weight in excess of 5 kg (females are considered to be lighter).

Monitoring: Radio-transmitter neck collars used weighed 80 g (minimal in comparison with sloth body weight) and were loose-fitting so as not to hamper movement. Each sloth was observed from 07:00 to 17:00 hours during the 1-3 days monthly monitoring period. Data on activity budgets, home range size and diet were collected.

Activity budgets: Four main activity states were recorded and quantified i.e. resting, feeding, moving and grooming.

Home range: The total horizontal distance travelled by a sloth was recorded as day-range length i.e. the distance travelled between 07:00 to 17:00 hours. Individuals were not monitored at night but the total horizontal distance travelled between the last position of one day and the first position of the next was calculated. The two distance values (diurnal and nocturnal) were added to give the total distance travelled in a 24 h period. Distances were measured using a 50 m long tape measure and direction of movement recorded using a compass. Movements over the monitoring period were plotted on a 1:1,000 scale map to enable an estimation of home range size to be made.

Diet: Sloth diets were recorded by recording the time an individual spent eating a particular plant species.

Temporal changes in activity budget: The monitoring results showed that moving/resting and feeding time, and daily distances travelled were not related to time (in days) after translocation release. It was expected that initially more time would be spent moving to familiarise themselves with the area in order to find food and suitable routes through the trees, to avoid predators, to locate potential mates and to establish a territory. However, no clear pattern was observed and there was a considerable amount of variability between individuals. Some were more active than others, some more diurnal and others more nocturnal. As the sloths came from nearby but different sites, each may have had to adapt slightly differently according to their preferences of certain liana or tree species in their diet. The ease each of the five individuals had in adapting may be a consequence of the similarity between the release site and the site of origin.

Sloths explored their respective areas more intensively in the first six months after release but minor changes in home range were detected even after three years. In the first six months, sloths were more frequently seen on lianas and trees at atypically low elevations only 1-3 m above the ground. This suggests that initially they may have had difficulties in finding safe routes to traverse between trees higher in the canopy and were thus having to descend to do so, whilst at the same time exposing themselves to greater predation risk.

Suitability of radio-collars: The equipment used proved successful for monitoring. Only one sloth had to be sedated for the collar to be fitted. In more than 1,000 h of observation there were only a few occasions in the first two weeks when the sloths were seen to scratch at their collars. No other agitation caused by the collars was noted.

Translocation success: During the monitoring periods (10 months to three years dependent upon the individual) none of the sloths showed visible signs of weight loss, disease or sickness; none were predated. However, of three young born (one of the translocated females gave birth to two, perhaps all three) all were predated. Given the timing and the gestation period (6 months) this female must have mated with a resident male.

Conclusions: Given the longevity and breeding success (despite subsequent predation of the young) of the study sloths, translocation appears to have been useful. Source and release sites should be floristically and ecologically similar but exactly what size of forest is needed to support a viable sloth population is unknown at present. The authors advocate that translocation may be appropriate to an area of forest as small as 50 ha.


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