Background and ResearchWildlife tourism has been considered a useful tool for conservation in some contexts and found to cause diverse effects on biodiversity. We investigated the effect of the number of tourists on wild black howler monkeys’ ( Alouatta pigra) behavior at the Montes Azules Biosphere Reserve (MABR), in the Lacandona forest in Mexico.MethodsWe used 5-min focal animal sampling, during dry and rainy seasons. We recorded five common behaviors in three wild groups naturally exposed to different degrees of human disturbance (Station, River and Board) without tourists, 5 and 10 tourists.ResultsFive and 10 tourists increased locomoting and reduced socializing, however, differently affected activities’ allocation time in the monkeys’ groups: in Board, 10 tourists reduced monkeys feeding; ii) in River, 10 tourists reduced socializing; and iii) in Station, 5 tourists increased feeding and reduced socializing, and 10 tourists reduced socializing.ConclusionsWatching tourism activities affect behavior differently in groups of Alouatta pigra in the Montes Azules Biosphere Reserve in in the Mexican state of Chiapas, emphasizing the importance of regulating tourism programs for the conservation of endangered species.Implications for ConservationAlthough longer-term studies controlling for additional variables are needed to provide a more comprehensive understanding of the impact of tourism on wild howler populations, the results from this study remain valuable as a baseline for understanding such effects and for proposing initial strategies to reduce tourism-induced disturbance.