The long call frequency of male mantled howler monkeys (Alouatta palliata) varies across individuals. In a forest environment where visual contact is impossible at greater distances the long call is utilized for inter-group spacing and for male-male communication. As lower frequencies are capable of traveling longer distances, it is quite possible that there is a correlation between group size and long call frequency. This link lies in the premise that smaller groups have fewer individuals thus fewer males, and spread out less over the course of each day while obtaining food resources, thus the distance these males call over their lifespan is generally less than the males in a larger group. This thesis investigates the relationship between group size and long call frequency in mantled howler monkeys (Alouatta palliata) on Isla de Ometepé, Nicaragua. / Includes bibliography. / Thesis (M.A.)--Florida Atlantic University, 2013.