Red howler
Alouatta seniculus

TAXONOMY

Suborder: Haplorrhini
Infraorder: Simiiformes
Family: Atelidae
Subfamily: Alouattinae
Genus: Alouatta
Species: macconnelli, sara, seniculus
Subspecies: A. seniculus arctoidea, A. seniculus juara, A. seniculus seniculus

Other names: A. sara: Bolivian red howler monkey; A. seniculus: red howler monkey, red howling monkey; rode brulaap (Dutch); hurleur roux (French); aullador amazónico, coto rojo, guariba vermelha, mono araguato (Spanish); röd vrålapa (Swedish); A. macconnelli: A. s. insulanus, Guyanan red howler, Trinidad howling monkey; A. s. juara: juruá red howling monkey; guariba vermelha (Spanish); A. s. seniculus: Colombian red howling monkey; guariba vermelha (Spanish).

The taxonomy of red howler monkeys is debated. Groves (2001) lists three subspecies of A. seniculus; A. s. arctoidea, A. s. juara, and A. s. seniculus. In their taxonomic review, Rylands et al. describe seven subspecies of the type, A. s. seniculus, A. s. insulanus, A. seniculus ssp. (formerly stramineus), A. s. amazonica, A. s. juara, A. s. puruensis and A. s. arctoidea (2000). Groves subsumes A. s. amazonica and A. s. puruensis under A. s. juara. In addition, he folds both A. s. ssp. (formerly stramineus) and A. s. insulanus into A. macconnelli (Groves 2001) (for a description of the differences in taxonomy see Rylands 2001). Thus, both the Guianan and Trinidad red howler monkeys are listed here as A. macconnelli. Otherwise, Groves' taxonomy of A. seniculus and its subspecies is followed.

MORPHOLOGY

Photo: Luiz Claudio Marigo

Red howlers are a member of the Atelinae, a subfamily of primates that includes the heaviest of the New World Monkeys (Di Fiore & Campbell 2007). (Average weights for males can range between 6 and 7.6 kg (13.2-16.8 lbs) while female weight averages range between 4.5 and 6.3 kg (9.9-13.9 lbs) in the wild (Thorington et al. 1979; Camacho & Defler 1985; Ayres JM 1986 cited in Ford & Davis 1992; Rodríguez & Boher 1988). Head and body length in adults averages 52.3 and 57.0 cm (20.6 and 22.4 in) in males and 46.8 and 49.7 cm (18.4 and 19.6 in) in females (Thorington et al. 1979; Rodríguez & Boher 1988). Sexual dimorphism of weight ranges between populations, but males are larger than females with females averaging between 69 and 95 percent of the body weight of the male (Thornington et al. 1979; Camacho & Defler 1985; Ayres 1986 cited in Smith & Jungers 1997; Rodríguez & Boher 1988; Smith & Jungers 1997). The tail is prehensile and is somewhat longer than the head and body together, averaging 65.5 cm (Thorington et al. 1979; Bergeson 1993; Richard-Hansen et al. 1999). Pelage is predominantly red, red-orange or golden red (Hill 1962; Thorington et al. 1979; Crockett pers. observ. cited in Crockett & Eisenberg 1987). Dorsal surfaces are golden red and the ventral surfaces are darker than the rest of the body, especially in the beard area, ranging from black to brown and maroon (Hill 1962; Crockett pers. observ. cited in Crockett & Eisenberg 1987). The face is blue-black with few hairs (Hill 1962). Variation in the darkness of the red pelage exists between locations and may reflect climatic variables (Thorington et al. 1979). There are no color differences between males and females (Hill 1962).

Bolivian red howlers (Alouatta sara) are brick red, with slightly darker and more reddish limbs, head and base of tail. In addition, their body size is larger than A. seniculus (Groves 2001).

One of the most characteristic features of the red howler, and indeed of the genus Alouatta as a whole, is the large hyoid bone, functioning to deepen the pitch, resonate, and amplify the species' vocalizations (Thornington et al. 1979; Crockett & Eisenberg 1988). Among the howlers, the hyoid in the red howler is largest and there is significant sexual dimorphism in its size, with male hyoid volume averaging 69.5 ml (2.4 oz) and female hyoids averaging 12.5 ml (0.4 oz) (Sekulic 1981 cited in Crockett & Eisenberg 1987; Crockett & Eisenberg 1987).

Red howlers travel most frequently occurs on tree branches and lianas but can occur arboreally as well as terrestrially (Schön Ybarra 1984; Youlatos & Gasc 2001). The most important mode of movement is clambering, followed by quadrupedal walking and running (Youlatos & Gasc 2001). Travel is mostly slow quadrupedal progression (Fleagle & Mittermeier 1980). Bipedalism and tripedalism are infrequent compared to quadrupedalism (Schön Ybarra 1984). Gap crossing, especially in the upper canopy, is mainly by bridging, in which the monkey maintains contact with supports with at least one of its extremities or its tail at all times (Youlatos 1993; Youlatos & Gasc 2001). Leaping is rarely used to cross gaps (Fleagle & Mittermeier 1980; Schön Ybarra 1984).

One unique form of locomotion is the vertical descent in which the red howler will face the ground and walk quadrupedially down a support with the tail helping to control the descent (Youlatos & Gasc 1994). Suspensory postures are typically seen during feeding and rarely during resting, and normally consist of tail suspension. Red howlers will stand both bipedally as well as quadrupedally, and other postures include reclining and sitting (Schön Ybarra 1984). Red howlers are capable of swimming and are able to cross moving water 200 m (656.2 ft) or greater in width (Hernández-Camacho & Cooper 1976; Soini 1986; Izawa & Lozano 1990b). In addition, the species will also cross savannah and other types of open ground on foot, often during group movements (Neville 1977; Hernández-Camacho & Cooper 1976; Rudran 1979).

Alouatta seniculus range (in red)

In captivity, red howlers have lived past 22 years old (Weigl 2005).

RANGE

Red howlers are found only in neotropical South America. They live in a number of countries including Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, Trinidad and Tobago, and Venezuela (http://www.cites.org). In general, the red howler range extends from northwest Colombia east and south to the river Amazon in eastern Brazil. In addition, they are found east of the Andes down the western coast of South America from Colombia through Peru and northern Bolivia and east into western Brazil as far as the rivers Purus and Juruá (Napier 1976; Wallace et al. 1998). Within their extensive range however, there are often many areas where they are not found, probably due to ecological factors (Iwanaga & Ferrari 2002). Subspecifically, A. s. seniculus is found in northern Colombia and northwestern Venezuela. A. s. arctoidea is found along the coast of Venezuela in the Rupununi savannah and Paramaraibo. A. s. juara is found mostly in Brazil and likely ranges into Ecuador, northern Peru, Colombia and Venezuela. A. macconnelli are found only in Trinidad and Guyana, and into Brazil north of the eastern parts of the Amazon river (Groves 2001). A. sara are found in the Bolivian Amazon (Cortés-Ortiz et al. 2003). Often there are not discrete demarcations between subspecies (see Crockett 1998a:553 for a map).

HABITAT

Red howlers can be found in a large variety of habitats within its range. They are found in tropical rain, humid, and dry forests, high terra firma forest, southern forests, mora forests, premontane and lower montane forests, cloud forests (including oak forests), southeast seasonal forests, swamp forests, Igapo forests (seasonally flooded blackwater forest) as well as other seasonally inundated forests, Bajos (floodable lowlands), transition forest, low seasonal forests, semi-deciduous and deciduous seasonal forests, floodplain forests, river terraces, riparian forests, swamp woodlands, eastern Wallaba forests, marsh woodlands and swamps and cacao plantations (Hernández-Camacho & Cooper 1976; Rudran 1979; Braza et al. 1981; Gaulin & Gaulin 1982; Cordero & Boher 1988; Yoneda 1990; Wallace et al. 1998; Youlatos 1998; Palacios & Rodriguez 2001; Lehman 2004).

An example of this widespread use of habitat is in Guyana, where they are found in every forest habitat type in the country (Lehman 2004). The widespread use of forest habitats is seen in Colombian red howlers as well where the species is found at high altitudes, absent only from forests near the alpine treeline (Gaulin & Gaulin 1982). While red howlers are capable of occupying a variety of forest types, in Amazonia, they do not live in habitats more than 1.6-1.8 km (1.0-1.1 mi) inland and they prefer lake and river edge habitat over terra firma forests (Peres 1993; Defler pers. comm. & Peres and Defler pers. comm. cited in Palacios 1998; Palacios 1998).

Photo: Roy Fontaine

Preferred feeding trees have trunks between 20 and 29 cm (7.9 and 11.4 in) in diameter (Yoneda 1990). Lower strata, including those close to the ground, are sometimes used for feeding but the species is frequently and most often found in higher forest strata. When sympatric with other primates, howlers prefer higher strata than the other species in the habitat (Soini 1986; Yoneda 1988; Peres 1993). Finally, red howlers can live in very small forest patches and secondary growth (Hernández-Camacho & Cooper 1976). The altitudinal limit of the red howler distribution is 3200 m (10498.7 ft) in the central Andes (Hernández-Camacho & Cooper 1976).

Due to its large distribution, different red howler habitats have different temperature and rainfall totals as well as differing in seasonality. In one study in the Andes at an altitude of 2300 m (7545.9 ft) in lower montane wet forest at Finca Merenberg, Colombia, temperatures were recorded to range between 8.5 and 21°C (47.3 and 69.8°F) and to average 12°C (53.6°F). At the same site, annual rainfall was 194.2 cm (76.5 in) with January as the driest month, and March the wettest (Gaulin & Gaulin 1982). At the Estación Biológica Caparú (EBC) in southeastern Colombia in the lowland tropical rain forest, rainfall averages 383.6 cm (151.0 in) yearly, with the lowest rainfall in September with 25.8 cm (10.2 in). There is no discrete dry season at this study site (Defler & Defler 1996). In northern Venezuela in the Barlovento region, mean annual temperature ranges from 25-28°C (77-82.4°F) with between 180 and 240 cm (70.9 and 94.5 in) of rain yearly. Most of the yearly rainfall occurs during the May-January rainy season at this location (Cordero & Boher 1988).

ECOLOGY

Due to its expansive range, the ecology of the red howler can vary significantly between study sites. Red howlers are, for the most part, herbivores and are predominantly frugivorous and folivorous, consuming mainly fruits and fruit pulp and leaves, supplemented by roots, flowers, epiphytes, seeds, berries, drupes, petioles, leaf buds, bark, wood, vine and liane parts and other plant material (Braza et al. 1983; Soini 1986; Neves & Rylands 1991; Julliot 1996a; de Thoisy & Richard-Hansen 1996; Palacios & Rodriguez 2001; Simmen et al. 2001). Common foods include plants from the genera Ficus, Clarisia, Xylopia, Cecropia, Ogcodeia, and Inga (Soini 1986). In general, red howlers prefer medium or large fruits with juicy pulp and that are bright in color (Julliot 1996a). Of the neotropical primates, they are likely the most folivorous as well, preferring young leaves as opposed to mature leaves (Gaulin & Gaulin 1982; Neves & Rylands 1991; Julliot 1992). The number of plant species eaten can be quite high, with as many as 195 species from 47 families being consumed although relative to usual exploitation; this number is exceptional and probably reflects high biodiversity and food availability at the study site (Julliot 1992; Julliot & Sabatier 1993). The species is also an important seed dispersal mechanism for the plants which it consumes (Andresen 2002).

Fruit availability in red howler habitat is often very seasonal and as a result, its relative importance in the diet varies throughout the year and between study sites. Thus, at some times during the year, the species can be described as predominantly folivorous while at other times they are predominantly frugivorous (for an example see Simmen et al. 2001). In Colombia at Tinigua National Park, red howler diet varies with food availability, but the two main staples are fruits and leaves which range between 10-49% and 43-76% of the diet respectively throughout the year. In the fruit scarcity period at the end of the wet season at this location, between September and November, leaves form a greater percentage of the diet than fruits. Seeds (2-8%), flowers (3-6%) and other foods (1-2%) make up the rest of the diet over the course of the year. Also at Tinigua, fruit abundance goes up during the beginning of the wet season (March-May) and during the dry season (December-February) (Stevenson et al. 2000). In Peru at the Pacaya-Samiria National Reserve, fruit availability is similar to that at Tinigua except for a general scarcity in the dry season. At this study site, feeding time was divided into fruit (72%), leaves (25%) and flowers (3%) and leaves are eaten year-round (Soini 1986). Red howler monkeys do not need to drink water and thus can live in areas away from natural water (Crockett 1998b). Red howlers have also been known to eat soil at natural saltlicks and to eat termite nest material, doing so every two or three days (Izawa & Lozano 1990a). In addition, a solitary male howler was observed catching and consuming green iguanas in French Guiana; however this is the only recorded example of predatory behavior in the species and may be unique to this one individual (de Thoisy & Parc 1999).

Photo: Roy Fontaine

Red howlers, a diurnal species, show differences in daily activities between the dry and wet seasons. In Venezuela during the dry season, activities on a daily basis consisted of sleeping (37.9%), snoozing (24.0), feeding (19.8%) and locomotion (18.4%). During the rainy season, percentages of daily activities changed to sleeping (43.2%), snoozing (18.2%), feeding (23.8%), and locomotion (14.8%) (Braza et al. 1981). Elsewhere, activity rates are similar, with over half of the time spent resting with feeding and traveling making up the rest of the activities for the day (Schön Ybarra 1984; Neves & Rylands 1991). The predominance of resting activity in the red howler has been proposed to be the result of their highly folivorous diet and the difficulties associated with leaf digestion (Gaulin & Gaulin 1982). In the rainy season, more time is spent feeding than in the dry season and less time is spent resting (Sekulic 1982c). Daily during the dry season, there are two main feeding bouts--one intense bout in the morning and one in the afternoon, a pattern followed in the Andes as well (Sekulic 1982c; Gaulin & Gaulin 1982). In addition, there can be up to three or four smaller feeding bouts throughout the day. A general pattern follows of more fruit being eaten in the earlier hours of the day and more leaves later in the day (Gaulin & Gaulin 1982). Daily activities, especially feeding, often start before the sun rises but stop before nightfall (Soini 1986). Red howlers spend the night in the canopy, huddled in groups (Soini 1986).

Home range can vary between .03 and 1.82 sq. km (.01 and 0.7 sq. mi), but in most studies, ranges are at the lower end of that variance (Braza et al. 1981; Sekulic 1981; Gaulin & Gaulin 1982; Soini 1986; Izawa 1997b; Kimura 1999; Yumoto et al. 1999; Palacios & Rodriguez 2001). There is some indication that home ranges are stable (Izawa 1997b). Home ranges often have some overlap with those of other troops and thus, the species is not strictly territorial (Sekulic 1981; 1982; Izawa 1997b; Kimura 1999). Sleeping trees are located in exclusive home range areas as well as areas of overlap with the home ranges of other troops (Sekulic 1982c). Daily path averages between 980-1150 m (3215.2-3773.0 ft) per day, but can range between 340 and 2200 m (1115.5 and 7217.8 ft) (Sekulic 1981; Gaulin & Gaulin 1982; Yumoto et al. 1999; Palacios & Rodriguez 2001).

A possible instance of tool use or object manipulation was observed in which a wild male red howler was observed to hit a two-toed sloth (Choloepus didactylus) repeatedly with a stick, however the reason for this behavior is unknown (Richard-Hansen et al. 1998).

Due to its large range and extent of occurrence, the red howler is sympatric with a number of primates. These include members of the genera Callithrix, Saguinus, Saimiri, Aotus, Callicebus, Pithecia, Cacajao, Cebus, Lagothrix, and Ateles (Peres 1997b). Spider monkeys (Ateles paniscus) are displaced by red howlers when encountered in the same fruit tree (Simmen 1992). In addition, white-tailed deer (Odocoileus virginianus) will form feeding associations with red howlers by remaining below the arboreal primates and collecting otherwise inaccessible foods accidentally dropped to the forest floor by the monkeys (Agoramoorthy 1997).

Raptors are predators of red howlers. Harpy eagles (Harpia harpyja) have been observed attacking, killing, and consuming adult howlers and the species is particularly vulnerable in forest edge habitats and open forest (Eason 1989; Peres 1990; Sherman 1991). Other evidence for predators includes strong circumstantial evidence of jaguar (Panthera onca) predation on the species that was not directly observed (Peetz et al. 1992). Potential but unconfirmed predators of red howlers include pumas (Felis concolor), foxes (Cerdocyon thous), ocelots (Leopardus pardalis), spectacled caimans (Caiman crocodiles) and Boa constrictor snakes (Sekulic 1981; Crockett 1996).

Communal defecation is characteristic of red howlers although sometimes individuals will defecate alone (Andresen 2002). Usually the group will simultaneously defecate from the same tree or group of trees, a behavior that usually occurs in the morning after waking up and at midday after the resting period (Braza et al. 1981; Julliot 1986b).

Content last modified: November 26, 2007

Written by Kurt Gron. Reviewed by Carolyn Crockett.

Cite this page as:
Gron KJ. 2007 November 26. Primate Factsheets: Red howler (Alouatta seniculus) Taxonomy, Morphology, & Ecology. <http://pin.primate.wisc.edu/factsheets/entry/red_howler>. Accessed 2008 May 17.