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 (Native )

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).

Average mass: 6.4 - 11.4 kg.

Average length: 70 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

• Terrestrial

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).

Average elevation: 400 m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: rainforest

Other Habitat Features: riparian

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).

Plant Foods: leaves; fruit; flowers

Primary Diet: herbivore (Folivore , Frugivore )

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

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).

Known Predators:

• jaguars (Panthera onca)
• pumas (Puma concolor)
• harpy eagles (Harpia harpyja)

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 ; tactile ; acoustic ; chemical

Other Communication Modes: choruses

Perception Channels: visual ; acoustic

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

Average lifespan

Status: wild: 20 years.

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

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).

Breeding interval: Mexican black howler monkeys reproduce yearly.

Breeding season: Mexican black howler monkeys may breed throughout the year.

Average number of offspring: 1.

Average gestation period: 180 days.

Range age at sexual or reproductive maturity (female): 3 to 4 years.

Range age at sexual or reproductive maturity (male): 3 to 4 years.

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

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).

US Federal List: threatened

CITES: appendix i

IUCN Red List of Threatened Species: endangered

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

Negative Impacts: crop pest

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