Alouatta pigra

Geographic Range

Alouatta pigra is found in Belize, northern Guatemala, and southeastern Mexico ("Belize Zoo", 2007; Gonzalez-Kirchner, 1998). They are endemic to the largest tropical rain forest region of Mesoamerica, Selva Maya, which encompasses over 4 million hectares of land in these three countries (Estrada et al., 2004). They are the only howler monkey species on the Yucatan peninsula, and are found in a reduced area of the Yucatan (Estrada et al., 2004; Gonzalez-Kirchner, 1998). They inhabit the Mexican states of Campeche, Quintana Roo, and Chiapas (Estrada et al., 2004). Populations have been found and heavily studied at the Mayan sites of Calakmul and Yaxchilán, Mexico, and Tikal National Park, Guatemala (Estrada et al., 2004). They are widespread throughout Belize.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

The habitat of Alouatta pigra is varied, but is typically tropical forests. They are known from lowland, deciduous, semi-deciduous forests, and evergreen forests (Belize Zoo, 2007; Gonzalez-Kirchner, 1998). They are known from pristine tropical rainforest to riverine forests, and can be normally found at low elevations in riparian forests of less than 400 m, although black howlers have been found at elevations higher than 500 m (Estrada et al., 2004). In riverine habitats they usually avoid riverbank areas and inhabit inland areas (Estrada et al., 2004). They prefer larger trees and usually inhabit the middle to upper canopy (Gonzalez-Kirchner, 1998). Although they have a wide habitat range, A. pigra has lower rates of success in areas disturbed by humans (Gonzalez-Kirchner, 1998).

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• rainforest rainforest

• Other Habitat Features
• riparian riparian

Physical Description

Alouatta pigra is one of the largest monkeys in the Americas. It averages 70 cm long, excluding the tail, which is slightly longer than its body length ("Belize Zoo", 2007). It is the largest and most sexually dimorphic of the howler monkeys, with an average weight of 11.4 kg for males and 6.4 kg for females (Fleagle, 1999). They are characteristically covered by black hair, which is a bit longer near the throat, and they have white genitalia (Treves, Drescher, & Snowdon, 2003). Males have a pink scrotum, which distinguishes Alouatta pigra from Alouatta palliata (Horwich, 1983a). Young retain pale fur until 9 to 10 weeks of age (Treves, Drescher, & Snowdon, 2003). Like other members of Atelidae , A. pigra has a prehensile tail with gripping pads (Fleagle, 1999).

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

Generally, only the dominant males or other males with high social status in the troop will copulate with females. The alpha male copulates more frequently and with more females at the peak of their cycle, which lasts two to four days (Van Bell, 2006). As a result of the social standing necessary to have the privilege of mating, males often mate later in life than females (Van Bell, 2006). Females seem to have reproductive success at a younger age, and, regardless of social position, copulate multiple times per cycle (Van Bell, 2006).

Van Bell’s (2006) description of the mating behavior of Alouatta pigra begins with the male sniffing the urine of the female and licking the female genitalia to detect her stage in the estrus cycle. To demonstrate interest, both the male and the female flick their tongue in and out of their mouth. Observational studies also show that females may incite mating by grabbing the hairs on a male' face. During the mating period, the pair mutually stay together for a few days and perform multiple copulations. The male usually mounts the female, holding on to her shoulders with his hands, and sometimes will use his feet to grasp as well. Generally, copulation lasts 30 seconds to one minute (Horwich, 1983b).

• Mating System
• polygynous polygynous

Sexual maturity is reached at the age of four years old ("Belize Zoo", 2007). However, males from 3 to 4 months of age already have a pale pink pigmented scrotum with descended testes (Horwich, 1983a). Researchers have been unable to detect any visual indications of the female estrus cycle in Alouatta , and there has not been much research on reproductive behavior and biology in general. Most research on reproduction is based on hormones collected from fecal matter in conjunction with information about the ages of individuals from which the fecal samples were collected (Van Bell, 2006). The female estrus cycle lasts from 11 to 24 days, peak time for conception lasts 2 to 4 days (Van Bell, 2006).

Mexican black howler monkeys do not exhibit seasonality in reproduction, possibly because their diet of leaves and unripe fruits is not seasonal in availability (Crockett & Rudran, 1987). There are slightly fewer births when new leaves and fruits emerge (Van Bell, 2006). Pregnancy lasts about 180 days. Offspring of both sexes often do not stay with their original troop (Kitchen, Horwich, & James, 2004).

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

Mexican black howler monkeys have single births ("Belize Zoo", 2007). Males in this species commit infanticide, possibly with the aim of limiting the sizes of their troops (Knopff & Pavelka, 2006). Females care for their young for 12 months after birth, providing direct care and protection from predators and adult males. Parenting is an individual role, as other members of the troop normally do not help raise offspring. Mothers are rarely far away from their newborns and are watchful for dangers to their young (Treves, Drescher, & Snowdon, 2003). However, as their young grow past the neonatal and infant stage, they are accorded a much greater range of freedom.

• Parental Investment
• altricial altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • protecting
    • female
• post-independence association with parents

Lifespan/Longevity

The average lifespan of Mexican black howler monkeys is 20 years ("Primate Info Net", 2004).

Behavior

Mexican black howler monkeys live in groups of 4 to 11 individuals (Estrada, 2004; Gonzalez-Kirchner, 1998). Adults make up about two thirds of a group, and the sex ratio is almost equal, about 4:3, although these numbers can vary quite widely (Estrada et al., 2004). Groups are more terrestrial than those of other howler monkeys. Aside from sleeping, Mexican black howler monkeys spend most of their time resting (about 70%), followed by feeding (18%), moving (5%), and socializing (1.2%) (Behie & Pavelka, 2005). Another study showed that they spend about 77% of their time resting, followed by about 15% feeding, 5% moving, and less than 1% socializing (Behie & Pavelka, 2005). Their long periods of inactivity are to promote the digestion of leaves, as they lack many adaptations common to other folivorous mammals (Kitchen, Horwich, & James, 2004).

A typical group consists of one dominant alpha male, a few females, their offspring, and occasionally extra males (Treves, Drescher, & Snowdon, 2003). Subordinate males are probably involved in group defense (Kitchen, Horwich, & James, 2004). Occasional lone males have been recorded (Estrada et al., 2004). These solitary males generally are trying to start their own groups (although they have also been found to usurp alpha males from already established groups) and can be used as indications of nascent groups. Groups that are recently formed are generally much smaller than longer-established groups (Gonzalez-Kirchner, 1998).

Generally, Mexican black howler monkeys have densities that range from 6.3 to 89.5 individuals per square km, lower than most other howler monkey species (Estrada et al., 2004; Gonzalez-Kirchner, 1998). Group sizes are also smaller than most other howler monkeys (Knopff & Pavelka, 2006). Current research focuses on which factors, including social considerations, their inactive lifestyle, or intragroup food competition, limit group size. One hypothesis is that infanticide limits group sizes (Knopff & Pavelka, 2006). It is not clear, however, if it is small group size that causes high rates of infanticide, or vice versa. Also, reproductive success decreases when group size increases, naturally limiting group size (Knopff & Pavelka, 2006).

Mexican black howler monkeys uses arboreal quadrupedalism as their main mode of locomotion (Fleagle, 1999).

• Key Behaviors
• arboreal arboreal
• terricolous
• diurnal diurnal
• motile motile
• sedentary sedentary
• territorial territorial
• social social
• dominance hierarchies dominance hierarchies

Home Range

The size of the territories is dependent on the number of monkeys in the group. Territory sizes are from 3 to 25 acres and are announced by howling vocalizations.

Communication and Perception

Mexican black howler monkeys announce and defend group territories through howling vocalizations ("Belize Zoo", 2007). They are highly social animals Adult howlers are less social, while infant and adolescent howlers engage in most of the social interactions (Behie & Pavelka, 2005). Adults in a group will often howl when approached by one or a few solitary males who may be trying to take over the alpha spot in the troop (Kitchen, Horwich, & James, 2004). Other threats include these solitary males trying to commit infanticide and thus lowering the reproductive success of the current alpha male (Kitchen, Horwich, & James, 2004). Howling can last for over an hour and is low frequency and loud: about 88 decibels at a 5 m distance (Kitchen, Horwich, & James, 2004). The energy used in howling is still less, and the risk smaller, than in physical confrontation. When more than one male is present howling occurs in staggered rounds and, as a result, howling can be used to indicate the number of males present (Kitchen, Horwich, & James, 2004). This information is useful to a group in deciding whether or not to approach another group and initiate a physical confrontation (Kitchen, Horwich, & James, 2004). The howls of females are aurally different from those of males, but they also participate in group howling.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• choruses choruses

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Mexican black howler monkey diet is varied. They are strict herbivores, consuming many plant parts, including flowers, fruits, and leaves ("Belize Zoo", 2007). All Alouatta species are highly folivorous. Alouatta pigra is one of the more frugivorous species in this genus. Their preferred food is fruit and they usually eat leaves only in conditions where frugivory is unfavorable (Behie & Pavelka, 2005). This allows them to have a flexible, adaptable diet that can adjust in cases of habitat change. Generally, a little more than 36% of their diet consists of fruits, followed by about 30% mature leaves, 25% new leaves and buds, and 5% flowers (Behie & Pavelka, 2005). Although they consume a significant amount of leaves, Alouatta pigra has a primitive digestive tract more suitable for frugivory; breaking down leaves therefore requires a longer digestion time, which explains the long inactive periods in their activity budget (Kitchen, Horwich, & James, 2004).

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • frugivore frugivore

• Plant Foods
• leaves
• fruit
• flowers

Predation

Mexican black howler monkeys can howl to frighten away predators or alert others of a predator's presence. Mothers aggressively protect their young for a year against predators and other dangers (Kitchen, Horwich, & James, 2004). The greatest predatory threat to young black howlers is infanticide by adult males. Otherwise, there are few natural predators for Mexican black howler monkeys. Occasionally they are preyed upon by jaguars, pumas, and harpy eagles (Knopff & Pavelka, 2006). Other cats, large birds of prey, and large arboreal snakes are also potential predators (Treves, Drescher, & Snowdon, 2003). Humans have been known to illegally catch individuals for pets, and they are occasionally eaten by humans (Kitchen, Horwich, & James, 2004).

Ecosystem Roles

Mexican black howler monkeys are often found living in close conjunction with Ateles geoffroyi and other spider monkeys (Estrada et al., 2004). They are also important for the role they play in seed dispersal (Van Bell, 2006). Their frugivorous diet has helped disperse the seeds of some rainforest plants. Although they do not shy away from human contact and their presence is quite obvious due to their howling, Mexican black howler monkeys rarely interfere with human crops.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Mexican black howler monkeys are important members of the ecosystems in which they live. Their howling is a unique element of their Mesoamerican forests and their presence can attract ecotourism.

• Positive Impacts
• ecotourism ecotourism

Economic Importance for Humans: Negative

Mexican black howler monkeys occasionally raid crops, although this behavior is rare (Estrada, 2006).

• Negative Impacts
• crop pest

Conservation Status

Mexican black howler monkeys are endangered by hunting and habitat destruction. The forests in which they live and feed are often converted into pastures or agricultural plots. Human influence as a whole is causing significant fragmentation of A. pigra habitats (Estrada, 2006). Other factors resulting in declining populations are: disease, abnormal rainfall, human capture for pets, and natural disasters such as hurricanes (Gonzalez-Kirchner, 1998). In areas affected negatively by humans, Mexican black howler populations become smaller both in numbers and in area (Gonzalez-Kirchner, 1998). They have been listed by the IUCN as an endangered species since 2003. They were previously (as recently as 2000) considered lower risk/least concern (Cuarón et al., 2003). The U.S. Fish and Wildlife Service lists Alouatta pigra as a threatened species. In the next 30 years, the total population is predicted to decrease 74% (Cuarón et al., 2003). Primates from this region have been hunted and captured as pets, causing their populations to decline further (Estrada et al., 2004).

Other Comments

Alouatta pigra is commonly known as Mexican black howler monkeys, Guatemalan howler monkeys, and saraguatos.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Kimberly Lau (author), Yale University, Eric Sargis (editor, instructor), Yale University.

References

Behie, A., M. Pavelka. 2005. The Short-Term Effects of a Hurricane on the Diet and Activity of Black Howlers (Alouatta pigra) in Monkey River, Belize.. Folia Primatol. , 76: 1-9.

Crockett, C., R. Rudran. 1987. Red howler monkey birth data I: seasonal variation.. American Journal of Primatology , 13: 347-368.

Cuaron, A., P. de Grammont, L. Cortes-Ortiz, G. Wong, J. Silva. 2003. "2006 IUCN Red List of Threatened Species" (On-line). Alouatta pigra. Accessed May 08, 2007 at www.iucnredlist.org .

Estrada, A., L. Luecke, S. Van Bell, et al.. 2004. Survey of black howler (Alouatta pigra) and spider (Ateles geoffroyi) monkeys in the Mayan sites of Calakmul and Yaxchilan. Primates , 45: 33-39.

Estrada, A. 2006. Human and Non-human Primate Co-existence in the Neotropics; a Preliminary View of Some Agricultural Practices as a Complement for Primate Conservation.. Ecological and Environmental Anthropology , 2: 17-29.

Fleagle, J. 1999. Primate Adaptation and Evolution . London: Elsevier Academic Press.

Gonzalez-Kirchner, J. 1998. Group Size and Population Density of the Black Howler Monkey (Alouatta pigra) in Muchukux Forest, Quintana Roo, Mexico.. Folia Primatol. , 69: 260-265.

Horwich, R. 1983. Breeding behaviors in black howler monkey (Alouatta pigra) of Belize.. Primates , 24: 222-230.

Horwich, R. 1983. Species Status of the Black Howler Monkey, Alouatta pigra, of Belize. Primates , 24: 288-289.

Kitchen, D., R. Horwich, R. James. 2004. Subordinate Male Black Howler Monkey (Alouatta pigra) Responses to Loud Calls: Experimental Evidence for the Effects of Intra-group Male Relationships and Age.. Behavior , 141: 703-723.

Knopff, K., M. Pavelka. 2006. Feeding Competition and Group Size in Alouatta pigra. International Journal of Primatology , 27: 1059-1078.

Treves, A., A. Drescher, C. Snowdon. 2003. Maternal Watchfulness in Black Howler Monkeys (Alouatta pigra). Ethology , 109: 135-146.

Van Bell, S. 2006. Studies of hormonal cycles, sexual behavior and the phenology of reproduction in howler and spider monkeys.. Accessed May 03, 2007 at http://www.primatesmx.com/fecalhormones.htm .

2007. "Belize Zoo" (On-line). Black Howler Monkey: Alouatta pigra. Accessed May 03, 2007 at http://www.belizezoo.org/zoo/zoo/mammals/how/how1.html .

2004. "Primate Info Net" (On-line). The Life Spans of Nonhuman Primates. Accessed May 08, 2007 at http://pin.primate.wisc.edu/aboutp/phys/lifespan.html .