Survey of black howler (Alouatta pigra) and spider (Ateles geoffroyi) monkeys in the Mayan sites of Calakmul and Yaxchilan, Mexico and Tikal, Guatemala

Surveys of populations of spider and howler monkeys were conducted at the Mayan sites of Calakmul and Yaxchilan, Mexico and Tikal, Guatemala. The forests in which these sites are found are part of the largest landmass of tropical rain forests present in Mesoamerica, encompassing about 4 million ha. Triangulation of monkey vocalization combined with ground surveys was used to determine the presence of howler and spider monkey groups. Howler monkey mean troop size at these sites varied from 6.6 +/- 2.1 individuals in Yaxchilan to 7.5 +/- 1.9 in Calakmul to 8.7 +/- 2.2 in Tikal. Density estimates varied from 12.8 individuals/km(2) in Yaxchilan to 15.2 individuals/km(2) in Calakmul to 17.8 individuals/km2 in Tikal. Mean spider monkey subgroup size varied from 4.7 +/- 2.6 individuals in Tikal to 5.6 +/- 3.0 individuals in Yaxchilan to 7.7 +/- 3.8 individuals in Calakmul. Spider monkey density varied from 17.0 individuals/km(2) in Yaxchilan to 17.2 individuals/km(2) in Calakmul to 56.4 individuals/km(2) in Tikal. All sightings of both howler and spider monkeys at the three sites were in undisturbed rain forest vegetation and spider monkeys in general were more frequently sighted at higher tree heights than howlers. We discuss the value of further acquiring data on howler and spider monkey populations existing in extensive forest tracts and on the conservation value for both primate species of the forests surrounding the Mayan ruins found in this area of Mesoamerica.