Bioacoustics of Lagothrix lagothricha

Breeding. Female Humboldt’s Woolly Monkeys are sexually mature at c.6 years of age. They generally leave their natal group for another group at this time, although some evidence suggests that dominant females remain in their natal group. Mating begins soon after a female enters a new group. Males sometimes approach and follow receptive females, but females frequently follow males and solicit mating. Mating occurs throughout the year, resulting in births year-round, but with a peak when food is plentiful during the early rainy season (March—May) in the eastern Colombian Amazon and late rainy season to early dry season (July-December) in the western Colombian Amazon. All sexually mature males have access to the group’s females and copulate with them, but the number of copulations is positively correlated with the linear hierarchy among males. During copulation, both sexes give a special vocalization (click or “tooth chatter”), a rhythmical movement of the teeth with maximal exposure. Copulation is dorsal ventral, with the male behind the female and the female reclining on the branch. Copulation lasts 6-7 minutes. All adult males may mate with a receptive female, but the dominant male copulates most. Dependent young climb over the copulating individuals and look at the pair’s genitalia. Females emigrate from their group to a neighboring group at c.6 years of age and usually begin copulating soon after. There are very low levels of aggression toward new females, perhaps because they are quickly accepted by adult males. A single offspring is born after a gestation of 223-225 days. In a twelve-year study, females were found to have a 23-36-day reproductive cycle, with a birth interval averaging 36-7 months. Following birth, the female has a period of sexual inactivity averaging 23-4 months, but sexual activity, when reassumed, continues for an average of 7-2 months before she conceives again. Copulation can occur at any time, but there are times when females copulate more frequently; this is in December—May in the western Colombian Amazon. During copulation periods, cycles last 2:3-3-1 days (when copulation is frequent) interspersed by 11-3-14-7-day intervals with no mating. After conception, copulations become non-cyclic. Births are usually singleton, occasionally twins. Neonates are nursed for up to a year. They are carried ventrally at first but move to the mothers’ back after c.2 weeks. Adult males sometimes participate, carrying an infant on their back and actively guarding it. Both sexes are fully mature at c.8 years, but the first parturition is usually at c.9 years. Humboldt’s Woolly Monkeys may live for more than 30 years; the population under study at the Rio Duda site in Colombia includes a 31-year-old individual.