AbstractWe document the loss of all but the youngest member of a troop of six howler monkeys due to probable jaguar predation during a 7‐month period in 1988. The formation of Guri Lake resulted in forest fragmentation which forced monkeys into new and unfamiliar areas and altered the balance of predator and prey populations, and may thus have contributed indirectly to the success of the jaguar. The selection of defoliated (dead) trees for sleeping sites by the howlers may have directly increased the risk of predation. © 1992 Wiley‐Liss, Inc.