We studied habitat use and ranging patterns of five red howler monkey troops for six months in a lower montane forest in the Colombian Andes. The study area is a mosaic of mature and secondary forest and non-commercial ash, pine and oak plantations that were established as part of a reforestation program. Home ranges (10 ± 3 ha) and daily distances traveled (554 ± 248 m) were similar to those reported for lowland habitats. Home range use differed between groups using mature forest versus secondary forest and plantations, reflecting structural differences between habitat types. We estimated a density of 0.72 individuals and 0.1 groups per hectare. This high density is related to the protected status of the study area and the howler monkeys' behavioral plasticity, which has allowed them to colonize new environments such as plantations.

We studied the geographic distribution of the endangered black howler monkey, Alouatta pigra, in its southeastern range in eastern Guatemala along its putative contact zone with the mantled howler monkey, A. palliata. A distributional survey of both species was conducted through direct observations and interviews, and the data analyzed with GIS to detect potentially limiting geographic and ecological factors. Alouatta pigra was not associated with any specific vegetation type or altitudinal range, as it occurred in many forest types from the lowlands up to elevations of 2705 m a.s.l., in contrast to prior reports of it being restricted to elevations below 400 m a.s.l. and having a strong affinity for riverine forests. Alouatta palliata did not occur at the higher elevations. Distribution of both howler monkey species was unaffected by the presence of Ateles, by protection status of the survey site, or by hunting activities. Deforestation appears to have restricted both species in some areas. Throughout the southeastern range of A. pigra, we found no evidence for current sympatry with A. palliata, as their distributions are separated by a river barrier and unsuitable dry shrubland. Ecological preferences also seem to reinforce allopatry, with only A. pigra occurring in wet and cold montane forests of the Sierra de las Minas. Our data indicate that highland habitats in Mexico and Guatemala, previously considered unsuitable for A. pigra, may need to be evaluated for distribution assessments and management plans. Populations of A. pigra in the diverse protected ecosystems in eastern Guatemala may be an important component for conservation of the species.

Groups of the Guatemalan black howler monkey (Alouatta pigra) in a fragmented northern Guatemalan cloud forest in the Sierra Yalijux were analyzed for group composition and size using an ornithological census technique. Audio and visual records were combined to estimate each group's home range size. The 361 observations in 2002 estimated 50 individuals in seven groups. Two home range classes were observed with ≤ 1.87 ha and ≥ 2.87 ha. Compared to other recent studies, the density of A. pigra in the Sierra Yalijux is considerably higher than in other areas (83.3/km² vs. 15.1/km² in Quintana Roo and 23.0/km² in Palenque) but about half the density found in Belize (178/km²). We discuss the relevance of the ornithology assessment method for howler monkeys.