104 



NORTH AMERICAN FAUNA 75 



probably indicates that they are more visible during these months either because 

 they are moving more or they are just more easily seen in their preferred trees. 

 Several of the observed animals were in Cecropia trees, one of the favored food 

 sources of this species. They are often visible from the foot bridge over the Rio 

 Puerto Viejo, where they can be seen in the Cecropia trees on the south bank. 

 We observed a single three-toed sloth in Parque Nacional Braulio Carrillo at 200 m 

 in March 1986. 



Greene (in press) observed an aggressive interaction between two adult male 

 three-toed sloths at La Selva. This is the first such observation on free-ranging 

 sloths. He saw one sloth actively approach the other in a C. obtusifolia tree and 

 witnessed that they struck each with their forefeet and emitted high pitched vocaliza- 

 tions. The aggressive encounter lasted some 3 min and ended when one sloth rapidly 

 descended the tree. He also reported that 4 days later on 19 December 1987 "a 

 pregnant female sloth was seen in the same tree, and one week later a female with 

 young was seen ca. 100 m away." Greene (in press) concluded that these obser- 

 vations suggest that the social system and other natural history traits of sloths were 

 more complex than has been previously thought. Sloths are one of the primary 

 prey items taken by jaguars at La Selva (Greene, in litt.). 



A discussion of the taxonomy of algae found in sloth hair was provided by 

 Wujek and Timpano (1986) who described a blue-green alga, a branched, filamen- 

 tous red alga, and two species of coccoid green algae based in part on material 

 collected on sloths at La Selva. 



The biology of three-toed sloths, primarily summarized from research on Barro 

 Colorado Island, Panama, was reviewed recently by Montgomery (1983a). Ex- 

 cellent comprehensive reviews on the biology of sloths and other xenarthrans were 

 provided by Montgomery (1978, 1985). 



Specimens examined (2)— Puerto Viejo, Rio Sarapiqui, 300 ft [2 females, 

 UMMZ]. 



Family Choloepidae 



Choloepus hoffmanni 

 Two-toed Sloth, Perezoso 



Two-toed sloths are found from southeastern Nicaragua to northwestern 

 Venezuela and Colombia (Fig. 81). The subspecies Choloepus hojfmanni hojfmanni 

 is found throughout Costa Rica from sea level to at least 1,800 m. 



Two-toed sloths have been sighted on 14 occasions at La Selva. Observations 

 of this species have been made throughout the year. Adults accompanied by single 

 young have been seen on three occasions— twice during January and once in March. 

 We observed a single two-toed sloth at 200 m in Parque Nacional Braulio Carrillo 

 in March 1986. 



Specimens examined (2)— Volcan Barva [1 female, CAL; 1 female, MVZ]. 



