Alouatta guariba
brown howler
(Also: brown howler monkey)

Alouatta guariba is found primarily on the Atlantic coast of South America, mainly in Brazil's coastal forests (Chiarello 1993 B) (Chiarello, 1993-B)

Brown howlers prefer the Atlantic forests of Brazil and Argentina. They spend most of their time in the top level of the trees eating the leaves fruits and flowers. Their habitat, however, is becoming fragmented due to logging. Despite this fact, they are abundant in this habitat compared to other species of primates (Pinto 1993). (Pinto et al., 1993)

This is a sexually dimorphic species, with males weighing 1.5 times more than the females.

Alouatta guariba is commonly known as brown howlers, which aptly describes their reddish brown coat color. There are, however, many versions of this coat color (red, yellow, orange, which vary according to where the species lives, but they always maintain some of their distinctive brown (Emmons 1997).

A physical characteristic unique to all howler monkeys is their enlarged hyoid bone. This, along with their enlarged hypo-laryngeal apparatus, is much different than other primates, and allows for their distinctive roars (Chiarello 1995). (Chiarello, 1995; Emmons, 1997)

Alouatta guariba spend much of their time resting. Their activity pattern during the daylight hours for the entire year includes an average of 64% of the time spent resting. In addition to resting, they spend approximately equal amounts of time moving and feeding: 13% and 18.5% respectively, as well as allogrooming for about 2% of their day. Much their period of rest occurs around noon when the temperature is highest (Chiarello 1993 A)

All howlers are known for their loud calls, and Alouatta guariba are no exception. They do, however, present some key differences in this behavior. Most howlers give a "dawn chorus" in which they all howl in the morning. A. fuscus does not exhibit this, and in fact seems to reserve most of its howling for intergroup encounters. The purpose for this is hypothesized to be to conserve energy by avoiding energetically ineffiecient chases. By calling, and listening to the calls of the other males, A. fuscus males can gauge the size of their adversarial groups. Brown howlers can also have choruses during mid morning and afternoon (Chiarello 1995). (Chiarello, 1993-A; Chiarello, 1995)

Brown howlers feed mainly on leaves, flowers and fruit. The composition of their diet varies according to the area in which they live. Chiarello (1994) found that as much as 73% of the diet can be leaves, while it also has been reported that some brown howlers eat more fruit than anything else.

Their diet also varies according to season. During the autumn and winter brown howlers must spend more time feeding. This is due to the inferior quality of the diet at that time, as well as the higher demands on energy during those seasons (Chiarello 1994)

Leaves are the howlers main source of nutrients. Leaves have low nutritional content, especially the older leaves eaten by brown howlers. Animals who are folivorous generally have stuctural specializations to help them digest and extract nutrients. Alouatta guariba do not posses these specializations. Some believe that the sedentary nature of these howlers is the result of an energy conservation strategy directly correlated with their leafy diet (Milton 1978). (Chiarello, 1994)

They are often hunted for their meat (Emmons 1997).

Alouatta guariba is a species that is experiencing fragmentation and destruction of their habitat as well as illegal poaching. Because of this, the species is threatened with extinction (Pinto 1993). (Pinto et al., 1993)