Among the largest primates in the Americas and with one of the loudest calls in the animal kingdom, howler monkeys are iconic species of South American tropical forests. They live in several types of forest ecosystems, from dry to riparian and rainforest. Although the forests they inhabit are being increasingly lost to deforestation for agriculture, howler monkeys are categorized as “Least Concern” by the IUCN Red List, meaning that they are considered to be not threatened with extinction. However, increasing deforestation rates and the howler monkey’s susceptibility to yellow fever outbreaks call for a reassessment of their status.