This species is found up to 1,000 m in tropical forest including riverine forest and seasonally flooded forests. 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.

The howler monkeys are the large leaf-eaters of the South American primate communities. The molar teeth are particularly adapted for their 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 the spider monkeys, they are prehensile-tailed, with a naked patch of skin on the under surface at 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 howls (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. 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 and A. pigra, have the smallest, and their howls are more high pitched as a result.

Red howler groups are usually small, ranging in size from 2-16 animals and averaging 4-10 (Neville et al. 1988). 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 Nation Park in eastern central Bolivia. In the red howlers, there is usually only one dominant male in the group (occasionally two), others being sub-adults, or juveniles, along with a harem of two to five females. Unlike the spider monkeys, and related 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, of 5 ha up to 45 ha, depending on the type of habitat (Neville et al. 1988).

Howlers are the only New World primates which 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.

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) (as for A. seniculus seniculus in Crockett and Sekulic 1982).

Red List Category

Red List Criteria

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This species is patchily distributed in terra firme forest, but is most common in seasonally flooded forest and riverine forest.

Decreasing

The main threat to this species is hunting (mainly for subsistence use), which has led to local extirpations in some areas.

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

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)
Madidi National Park (1,571,500 ha).

It is listed on Appendix II of CITES.