This species is found in lowland tropical forest including riverine forest and seasonally flooded Amazonian forests, Andean foothill forest, and the gallery forests of the Beni wetland. During their primate surveys in the Noel Kempf Mercado National Park, Bolivia, Wallace et al. (1998) found Alouatta sara only (n=20) in igapó forest (seasonally inundated forest) along the Río Iteñez. In the neighbouring Rios Blanco y Negro Wildlife Reserve, Alouatta sara was also found intermittently and usually confined to riverine forests (Wallace et al. 2000). Nevertheless, in the Sub-Andean Tropical Forests of western Bolivia, A. sara is more commonly encountered in lowland tropical forests (WCS unpublished data).

The howler monkeys are the large leaf-eaters of South American primate communities. The molar teeth are particularly adapted for chewing leaves through shearing. They spend up to 70% of their day lying and sitting about quietly among the branches, fermenting leaves in their enlarged caecums. Like woolly- and spider monkeys, they have prehensile tails, with a naked patch of skin on the ventral side of the tip. Their most characteristic feature is the deep jaws which surround the enlarged larynx and hyoid apparatus, a resonating chamber. It is with this enlarged and highly specialized voice box that they produce their loud vocalizations (grunts, roars and barks). Howling sessions, usually involving the entire group, can be heard particularly in the early morning and are audible at distances of 1–2 kms (Drubbel and Gautier 1993). The red howlers (A. seniculus, A. arctoidea, A. macconnelli, A. juara, A. puruensis, and A. sara) have the largest voice boxes and the deepest roars, while the Mexican, Central American and northern Colombian mantled howlers, A. palliata, have the smallest, and their howls are more high-pitched as a result.

In general red howler monkey groups are small, ranging in size from 2 to 16 animals and averaging 4–10.5 (Neville et al. 1988, Di Fiore et al. 2011). For A. sara, Wallace et al. (1998) recorded an average group size of 3.3±2.0 individuals (range 1–7, n=18) in the Noel Kempff Mercado National Park in eastern Bolivia. In red howler groups, there is usually only one dominant male (occasionally two), others being sub-adults, or juveniles, along with a harem of two to five females. Unlike the spider monkeys, and due to the large proportion of leaves in the diet (up to 50% of the annual diet), the howler monkeys generally have quite small and broadly overlapping home ranges (Neville et al. 1988). The ranges of red howlers vary between 3.9 and 182 ha, depending on the type of habitat and perhaps on the species (See Di Fiore et al. 2011). There is no specific information available for A. sara.

Howlers regularly include mature leaves in their diet, although softer, less fibrous, young leaves are preferred when they are available. Their folivory and ability to eat mature leaves is undoubtedly one of the keys to their wide distribution and the wide variety of vegetation types they inhabit. Mature fruit is the other important food item, especially wild figs (Ficus) in many regions, but they also eat leaf petioles, buds, flowers (sometimes seasonally very important), seeds, moss, stems and twigs, and termitaria.

In the closely related A. arctoidea, as well as in other howler species, oestrus lasts 2–4 days, with intervals between oestrous periods of about 17 days. Interbirth intervals are generally about 16.6 months, although they may be shortened by the death of an infant to about 10.5 months (Crockett and Sekulic 1984). Mean gestation length is 191 days (range 186–194, n=6) for A. arctoidea (Crockett and Sekulic 1982).

Alouatta sara occurs in Bolivia and southern Peru (Ruiz-Garcia et al. 2016). In Bolivia, Anderson (1997) gives a range extending from the Department of Pando south along the Andean Cordillera (up to 1,200 m, Wallace and Rumiz 2010) and east into central Bolivia including the entire basin of the Río Beni and east as far the Mamoré-Guapore. Its sympatry with Alouatta caraya over a large part of its range east of the Río Beni is poorly understood (Buntge and Pyritz 2007), but the indications are that there may be some subtle, but distinct difference in habitat preferences, with red howlers prevailing in humid forest areas and seasonally flooded forest along major rivers (for example, igapó along the Río Iteñez) and A. caraya being found in drier, semi-deciduous forest and gallery forest in areas of savanna and chaco (see for example, Wallace et al. 1998, 2000). There are questions over whether all red howler monkeys in Bolivia should be considered A. sara, or whether those in the extreme east may represent A. puruensis (Wallace and Porcel 2010, Wallace and Rumiz 2010), however, genetic information is currently lacking, and for the moment all red howler monkeys in Bolivia are treated as A. sara (Wallace et al. 2010).

In Peru A. sara is found along the Madre de Dios, Tambopata and Urubamba rivers (Solari et al. 2006, Gregory et al. 2012, Ruiz-Garcia et al. 2016).

Extent of occurrence (EOO) and area of occupancy (AOO) are suspected to be undoing decline due to habitat degradation. Habitat loss appears to have resulted in close to 20% loss of the species' range in Peru (Shanee, S. unpublished data), based on an analysis using the distribution map and Peruvian government deforestation data published by MINAM (Ministerio del Ambiente). According to this unpublished analysis, the areas most severely impacted by illegal gold mining in Peru corresponds with part of the species distribution and a number of roads dissect these areas. This analysis also indicates that climate change, based on the IPCC (Intergovernmental Panel on Climate Change) predictions is set to adversely affect the species range with increased temperatures and changes in rainfall patterns.

Habitat degradation across the species range will likely continue into the future. For example, in the State of Rodonia, it has been estimated that between 32% to 47% of Rondonia’s native forest will be fully deforested between 2012 and 2050 (Piontekowski et al. 2019).

There are a number of protected areas within this species range:

Bolivia:

• Isiboro Sécure National Park (1,200,000 ha) (Brown and Rumiz 1986).
• Noel Kempff Mercado National Park (1,500,000 ha) (Wallace et al. 1998).
• Manuripi Heath National Reserve (1,884,000 ha) (Brown and Rumiz 1986).
• Ríos Blanco y Negro National Reserve (1,423,900 ha) (Wallace et al. 2000).
• Amboró National Park (180,000 ha) (Brown and Rumiz 1986).
• Pilon Lajas National Park (400,000 ha) (Brown and Rumiz 1986).
• Carrasco National Park (622,600 ha).
• Beni Biosphere Reserve (135,000 ha).
  
• Madidi National Park (1,897,750 ha).

Peru:

• Manu National Park (1,716,295 ha)
• Tambopata National reserve (274,690 ha)

It is listed on Appendix II of CITES.