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The population of black howler monkeys (Alouatta pigra) at the Lamanai Archaeological Reserve in northwestern Belize was studied for a total of 11.5 months during 2 wet and 2 dry seasons between October 1993 and May 1995. We estimated home-range size and range overlap of troops in order to examine territoriality, and tested the null hypothesis that the population is uniformly distributed throughout the reserve in order to examine habitat use. Home-range sizes were similar to those at Bermudian Landing, Belize, but smaller than those at Tikal, Guatemala. Mean home-range size was estimated as 15.3 ha with 52% overlap based on a 1.0-ha grid. There was no evidence for territoriality. Population distribution was generally uniform, but ruin sites appeared to be preferred habitat and edge habitat was least frequented.

The majority of the literature describing howling monkeys (Cebidae) has focused on only 2 of 6 species in the genus. These studies have revealed differences in behavior between species and differences within species at different locations. One study has been published describing the vocal patterns of the black howler monkey (Alouatta pigra). This species appears to differ markedly from previously described Alouatta. In an effort to further distinguish A. pigra from its congeners, we observed the vocal patterns of an additional population of black howler monkeys. This population exhibited a bimodal calling pattern similar to that previously described for A. pigra, but absent in all but one (A. fusca) of the other species in the genus. The bimodal pattern was evident in both the rainy and dry seasons, with peaks in the morning and afternoon. Midday and afternoon calling were significantly reduced in the dry season. We also made a detailed comparison between both populations to examine the function ...