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 of the afternoon peak. Contrary to the results of the previous study, we conclude that there is insufficient evidence to describe either of these populations as territorial.