| survey of black howler (alouatta pigra) and spider (ateles geoffroyi) monkeys in the mayan sites of calakmul and yaxchilán, mexico and tikal, guatemala. | surveys of populations of spider and howler monkeys were conducted at the mayan sites of calakmul and yaxchilán, 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+/- ... | 2004 | 14586803 |