Brief Summary

Comprehensive Description

    Venezuelan red howler
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    The Venezuelan red howler (Alouatta seniculus) is a South American species of howler monkey, a type of New World monkey, found in the western Amazon Basin in Venezuela, Colombia, Ecuador, Peru and Brazil.[3] The population in the Santa Cruz Department in Bolivia was split off as a separate species, the Bolivian red howler, in 1986,[4][5] and more recently, splitting off the population in northeastern South America and Trinidad as the Guyanan red howler has occurred.[1] All howler monkeys belong to the family Atelidae and the infraorder Platyrrhini (New World monkeys).


    Skull of Alouatta seniculus.

    Sexual dimorphism in this species is small; males range from 49–72 cm and females from 46–57 cm long.[6] The males weigh 5.4-9 kg, while females weigh 4.2–7 kg.[6] It has a long prehensile tail of 49–75 cm.[6] The tail is covered with fur except for the last third of the underside, which allows it to grab branches. The color of both males and females is a deep reddish-brown, and the color shade changes with age.[6] Their faces are surrounded by fur and they have stubby noses.

    The jawbone of the red howler monkey is large, especially the body of the mandible. The position of the foramen magnum is very posterior to make way for the expanded jaw and enlarged hyoid bone. Howler monkeys also have an inflated bulla, which is the bony encasement of the middle ear. This makes them an exception among other New World monkeys.

    The diurnal Alouatta seniculus is an arboreal primate, so it spends much of its time high in the canopy. Its preferred method of locomotion is quadrupedal walking with minimal leaping. Its long, prehensile tail also assists it by providing both support and grasping abilities. In addition, its hands and feet have a grasping pattern that allows it to better move about in the trees. This can be seen by the wide separation of the second and third digits of the hand.

    Social interactions

    It lives in groups of three to 9 individuals (usually five to seven).[7] The groups are polygynous, with only one or two males and the rest females and their offspring.[6] One male is the usually dominant monkey of the group, the alpha male, and he is responsible for leading them to new food sites and defending them. The females of the group are in charge of the offspring. Venezuelan red howlers are most active in the morning, when the group is on the move to find another feeding spot. These howlers are famous for their “dawn chorus”. These roaring and howling calls are performed mostly by the males in the group. The roars can be heard up to 5 km away in the forest, and make their presence known in the area.[6] This is also used to prevent confrontations between groups, which will prevent energy loss by avoiding physical fighting. Because of their low-sugar diets, conservation of energy is key. The calls also help in the scattering of the groups and lessens the competition over food.[6]

    Diet and dentition

    A. seniculus monkeys are folivores, which means their diets mainly consist of leaves, but they also rely on nuts, small animals, fruits, seeds, and flowers for important nutrients. These foods provide sugar necessary for growth and energy. The most important part of their diets is leaves, which they cannot live without for more than a week. They eat both older and younger leaves; however, the older leaves provide more nutrition. These howler monkeys are able to eat the fibrous leaves due to the structural aspects of their dentition. Narrow incisors aid in the ingestion of the leaves, and molars with sharp, shearing crests help them to better chew their food. In addition, they have complex stomachs to aid in the digestive process. Their hindguts and large intestines also help with digestion.[6] The hindgut contains bacteria that digest leaves and makes up a third of the Venezuelan red howler’s total body volume.[6]

    Like other New World monkeys, the Venezuelan red howler's dental formula (maxilla and mandible) is two incisors, one canine, three premolars, and three molars.


    The fierce sexual competition between males is due to an unbalanced sex ratio.[6] A female attracts males by moving her tongue around to initiate mating. If the male does not respond, she moves on to another mate.[6] The average gestation period is 190 days.[6] The infant will stay with the mother for 18–24 months. After males reach sexual maturity, they are expelled from their natal group.[6] The male must then invade a foreign group. There, the male kills off the other leader and whatever offspring the first leader sired. By doing this, the male is killing any possible competition. Less than 25% of offspring survive male invasions.[6]


    Traditionally, three subspecies of this howler are listed,[1] though Stanyon et al. (1995) concluded the number of chromosomal differences between A. s. sara and A. s. arctoidea (which resulted in A. s. sara being a considered a full species) was on a similar scale to that found between A. s. sara and A. s. seniculus by Minezawa et al. (1986).[3]

    A. s. juara has been described as a different species Alouatta juara.[8]


     src= Wikispecies has information related to Venezuelan Red Howler  src= Wikimedia Commons has media related to Alouatta seniculus.
    1. ^ a b c Groves, C.P. (2005). Wilson, D.E.; Reeder, D.M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 150. ISBN 0-801-88221-4. OCLC 62265494..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""'"'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
    2. ^ Boubli, J.-P.; Di Fiore, A.; Rylands, A. B. & Mittermeier, R. A. (2008). "Alouatta seniculus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 19 January 2012.
    3. ^ a b Urbani, B.; Boubli, J.-P. & Rylands, A.B. (2008). "Alouatta arctoidea". IUCN Red List of Threatened Species. Version 2008. International Union for Conservation of Nature. Retrieved 12 March 2009.
    4. ^ Minezawa. M., Harada; M., Jordan, O. C. & Valdivia Borda, C. J. (1986). "Cytogenetics of the Bolivian endemic red howler monkeys (Alouatta seniculus sara): accessory chromosomes and Y-autosome translocation related numerical variations". Kyoto University Overseas Research Reports of New World Monkeys. 5: 7–16.CS1 maint: Multiple names: authors list (link)
    5. ^ Mercado, Nohelia I. & Robert B. Wallace (2010). "Distribución de primates en Bolivia y áreas prioritarias para su conservación" (PDF). Mongabay.com Open Access Journal (in Spanish). Tropical Conservation Science. 3 (2): 200–217.
    6. ^ a b c d e f g h i j k l m n Normile, R. V. (2001). "Alouatta seniculus information". Animal Diversity Web. Retrieved 2008-07-30.
    7. ^ Louise Emmons & Francois Feer (1997). Neotropical Rainforest Mammals.
    8. ^ Gregorin, Renato (2006). "Taxonomia e variação geográfica das espécies do gênero Alouatta Lacépède (Primates, Atelidae) no Brasil". Revista Brasileira de Zoologia. 23 (1): 64–144. doi:10.1590/s0101-81752006000100005.
    • Heatwole, Alan M.. Monkeys and Apes. 1st. New York: Gallery Books, 1990.


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    Alouatta seniculus have the widest geographical distribution of all the New World primates. Red howler monkeys range throughout the northern half of South America, from Colombia to Bolivia.

    Biogeographic Regions: neotropical (Native )


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    Alouatta seniculus are slightly sexually dimorphic. Females have a body length of 46-57 centimeters; males, which are larger, have a body length of 49-72 cm. Both sexes have a long, prehensile tail of approximately 49-75 cm. The coat color of males and females is a deep reddish-brown, although the shade varies slightly with age. Red howlers have a large neck with tremendous lower jaw and hyroid bones, giving them a forbidding expression.

    (MacDonald, 1985) (Nowak, 1991).

    Range mass: 4.5 to 6.5 kg.

    Other Physical Features: endothermic ; bilateral symmetry


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    Terrestrial Biomes: forest ; rainforest

Trophic Strategy

    Trophic Strategy
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    Alouatta seniculus are primarily folivorous. Leaves are low in nutrients and sugars in comparison with other food choices, and red howler monkeys have two large sections in their hindgut which contain the bacteria needed to digest the cellulose in leaves. This change in anatomy results in a large gut that occupies one-third of their total body volume. In addition, their extremely deep lower jaw bones aid red howlers in chewing. Alouatta seniculus also improve their digestive efficiency by feeding primarily on tender young leaves and on some species of leaves that are unusually nutritious. In addition, they eat sugary fruits and flowers when these are available, but can sustain themselves for weeks at a time on only leaves, providing these are high in quality. Alouatta seniculus spend almost their entire lives near the top canopy of the forest, where such leaves are most abundant (Devore, 1965) (MacDonald, 1985).

    Plant Foods: leaves; fruit; flowers

    Primary Diet: herbivore (Folivore )


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    Perception Channels: tactile ; chemical

Life Expectancy

    Lifespan, longevity, and ageing
    provided by AnAge articles
    Maximum longevity: 25 years (captivity) Observations: One wild born animal was still alive after 22.8 years in captivity, making it as old as 25 (Richard Weigl 2005). It has been estimated that these animals live up to 25 years in the wild (http://www.demogr.mpg.de/longevityrecords), though this has not been confirmed.
    Life Expectancy
    provided by Animal Diversity Web

    Average lifespan
    Status: wild:
    25.0 years.


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    Due to such an unbalanced sex ratio, fierce sexual competition exists between and within red howler troops. Red howler males, which are expelled from their natal troop upon reaching sexual maturity, are forced to invade an outside group and gain admittance. Once they have accomplished this, they violently kill any infants present in the group. By killing infants in a newly invaded troop, a male can mate quickly and ensure that the new offspring of the group are his own. Mothers do try to protect their offspring against assaulting males. Unfortunately for the female, this is not particulaly successful; less than 25% of offspring survive a male howler invasion.

    The mating behavior of red howlers is another interesting aspect of their social interactions. Males and females often form consortships, an unusually close spatial relationship, before any sexual exchange has begun. Once these associations are established, sexual solicitations begin. Although seductive behaviors can be performed by both sexes, the female most often takes on the aggressive role. When attempting to attract a male, the female approaches him and moves her tonque rhythmically. The male may respond the same way, but if he does not, the female may simply try to entice another male.

    Mating System: polygynous

    Alouatta seniculus appears to breed throughout the year. However, in two habitats in Venezuela, the birth frequency is reduced during the early wet season, May through July. The estrous cycle ranges from 16-20 days, with the female being receptive for 2-4 days. Red howler females give birth for the first time around 5 years of age, while males usually do not father an offspring until approximately 7 years. Therefore, a female reaches sexual maturity a couple of years before a male.

    (MacDonald, 1985) (Nowak, 1991) (Smuts et. al, 1986)

    Breeding season: Red howler monkeys breed year round

    Average age at sexual or reproductive maturity (female): 5 years.

    Average age at sexual or reproductive maturity (male): 7 years.

    Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous

    Average birth mass: 263 g.

    Average gestation period: 190 days.

    Average number of offspring: 1.

    Average age at sexual or reproductive maturity (female)
    Sex: female:
    1475 days.

    Newborn A. seniculus are at first quite helpless and are carried around at the mother's belly. Young red howlers begin using their prehensile tails before they are one month old. An infant uses its tail to secure itself to its mother, for in this stage of its life the mother pays little or no attention to her offspring, and fails to give the baby any assistance!

    Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female); extended period of juvenile learning

Conservation Status

    Conservation Status
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    Although several other Alouatta species are endangered, A. seniculus has no special conservation status. However, red howlers have become rarer in some areas, most likely due to the destruction of their habitat. Fortunately, they are still adundant in Brazil (Nowak, 1991).

    IUCN Red List of Threatened Species: least concern


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    Due to their relatively large size, A. seniculus, along with other howler species, are hunted for food and are subject to commercial export (Nowak, 1991).

Other Articles

    provided by Animal Diversity Web

    Red howlers have an amusing reaction to rainy days during the tropical wet season. In response to heavy rains, they howl, either at the onset, or often at the sound of approaching rain, and sit hunched over until the rain ends (Clutton-Brock, 1977)!

    Red howler monkeys have overcome problems that are usually associated with having leaves as a principle food source, including their specialized jaw and stomach structures. Behaviorally, they (along with the other species in their genus) are unique in that they have developed the loudest vocalization of any animal in the New World. These adaptations have aided them in becoming an extremely successful primate--and yet they are still able to sleep for more than 15 hours a day!