Alouatta seniculusred howler monkey

Ge­o­graphic Range

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.

Habi­tat

Phys­i­cal De­scrip­tion

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
    9.91 to 14.32 lb

Re­pro­duc­tion

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.

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 number of offspring
    1
    AnAge
  • Average gestation period
    190 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    5 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    1475 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    7 years

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

Lifes­pan/Longevity

Be­hav­ior

Red howler mon­keys live in rel­a­tively large so­cial groups, con­sist­ing of ap­prox­i­mately 10 in­di­vid­u­als, with only one or per­haps two of the in­di­vid­u­als being males. Alouatta senicu­lus ex­hibit many in­ter­est­ing be­hav­iors. They are most fa­mous for their "dawn cho­rus", a deaf­en­ing roar that can be heard up to 5 kilo­me­ters away! These res­onat­ing howls, per­formed pri­mar­ily by the males of a group, are an­swered by all other howler troops within ear shot. This way, one troop can con­stantly in­form an­other of its pre­cise lo­ca­tion, thus avoid­ing an en­er­get­i­cally costly squab­ble over re­sources.

Dur­ing par­tu­ri­tion, a new­born usu­ally be­comes the focus of at­ten­tion of sev­eral other fe­males. Typ­i­cally, it is fe­males with­out in­fants of their own that are at­tracted to these in­fants. In these in­stances, the fe­males are ex­tremely gen­tle with the lit­tle ones, touch­ing them with their muz­zles and hands. They may even oc­ca­sion­ally en­cour­age the in­fant to crawl on them. Males also are known to tol­er­ate the ac­tiv­i­ties of in­fant howlers in their troop. Sim­i­lar to the adult fe­males, the male red howlers also allow the in­fants to climb all over them. This of course takes place long after the male has killed all off­spring that are not his own.

(Crock­ett, 1984) (De­Vore, 1965) (Haus­fater & Hrdy, 1984)

Com­mu­ni­ca­tion and Per­cep­tion

Food Habits

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

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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).

Con­ser­va­tion Sta­tus

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).

Other Com­ments

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!

Con­trib­u­tors

Re­becca V. Normile (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

Ref­er­ences

Clut­ton-Brock, T.H. 1977. Pri­mate Ecol­ogy. Aca­d­e­mic Press, NY.

Crock­ett, C. 1984. Nat­ural His­tory, vol. 93, 54-62.

De­Vore, I. ed. 1965. Pri­mate Be­hav­ior. Holt, Rine­hart & Win­ston, NY.

Haus­fater, G. & Hrdy S. ed. 1984. In­fan­ti­cide. Al­dine Pub­lish­ing Co., NY.

Mac­Don­ald, D. 1985. The En­cy­clo­pe­dia of Mam­mals. Facts on File Pub­li­ca­tions, NY.

Nowak, R. 1991. Walker's Mam­mals of the World. Johns Hop­kins Univ. Press, MD.

Smuts, B.; Ch­eney, D.; Sey­forth, R.; Wrang­ham, R. & Struh­saker, T. 1986. Pri­mate So­ci­eties. Univ. of Chicago Press, IL.