About Alouatta guariba (Humboldt, 1812)
The brown howler (Alouatta guariba), also called the brown howler monkey, is a species of howler monkey, a type of New World monkey. It inhabits forests in southeastern Brazil and far northeastern Argentina (Misiones). It lives in social groups of 2 to 11 individuals. Despite its common name "brown howler", this species shows notable color variation: some individuals are mostly reddish-orange or black. Two subspecies are recognized: the Northern brown howler (A. g. guariba), which is listed as critically endangered, and the Southern brown howler (A. g. clamitans).
The brown howler occurs in the Atlantic Forest of South America, across the Brazilian states of Bahia, Espírito Santo, and Rio Grande do Sul, as well as Misiones Province in Argentina.
Breeding Alouatta howler monkeys in captivity is difficult, so relatively little is known about the reproduction of this species. Brown howlers reproduce year-round, with no observed correlation between birth rates and rainy/dry seasons, or periods of higher availability of fruit or leaves. Researchers suggest that because the brown howler has a folivorous (leaf-eating) diet, conception is less dependent on maternal physical condition. The average interbirth interval (IBI) for this species is 19.9 months, which matches the average IBI of other howler monkey species. Neither infant sex nor the number of females in a population appears to have a significant effect on IBI. Only infant death reliably shortens a mother's interbirth interval, making it one of the few confirmed factors that affects brown howler IBI.
