Brown spider monkeys, Ateles hybridus, are restricted to subtropical and tropical moist lowlands in Venezuela and Colombia. There are two recognized subspecies of A. hybridus, Ateles hybridus hybridus and Ateles hybridus brunneus. The former occurs in both Colombia and Venezuela, inhabiting forests from the right bank of the Río Magdalena to areas extending into western parts of Venezuela. Ateles hybridus brunneus can only be found in Colombia, ranging between the lower Ríos Cauca and Magdalena in the Departments of Bolívar, Antioquia, and Caldas.

Biogeographic Regions: neotropical (Native )

The appearance of Ateles hybridus is similar to other species of spider monkeys and, as their common name indicates, spider monkeys have exceptionally long, slender limbs. Their forelimbs are longer than their hindlimbs and their intermembral index is approximately 105. They also have a long, thin, prehensile tail, which acts almost like a fifth limb. These features enable them to be highly suspensory and allow them to easily forage and travel in the high canopy. The length of the tail is around 75 cm and is highly flexible and distally hairless, with ridged skin for a better grip. The hands are hook-like, with four elongated, curved, fingers. The thumb is reduced, which facilitates swinging and gripping branches and is an adaptation to their strictly arboreal lifestyle. Spider monkeys are the biggest of all the New World primates, an adult male brown spider monkey weighs between 7.9 and 9.1 kg and an adult female weighs between 7.5 and 9 kg. The average body length for adult individuals is around 50 cm. Their coloration ranges from light brown to dark on upper parts including the head. The inner side of the legs, arms and tail are a lighter, more buff color. Another distinguishing characteristic of this species is the white triangular forehead patch but not all individuals possess this conspicuous feature. Some individuals also have pale blue eyes, but usually they are light brown.

Range mass: 7.5 to 10.5 kg.

Average mass: 8.5 kg.

Range length: 45 to 50 cm.

Average length: 47 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

• Terrestrial

Brown spider monkeys are arboreal and mainly found in high and lowland primary evergreen rainforest from 20 to 700 m elevation. They spend most of their time traveling and foraging in the high canopy, but they also use the middle and lower strata to a lesser extent. They rarely descend to the forest floor except for drinking water or eating soil. Brown spider monkeys are habitat specialists and prefer undisturbed old forests (primary forests) and rarely inhabit disturbed forests with less complete canopy (secondary forests). Primary forests have tall mature trees, a continuous canopy, an understory with little underbrush and significant bigger and more abundant fruiting trees than secondary forests have. One reason for their habitat choice is that their diet primarily consists of fruit.

Range elevation: 20 to 700 m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: rainforest

Brown spider monkeys are highly frugivorous and feed on a wide variety of fruits all year round. They specialize on ripe fruit, which comprises approximately 83% of their diet. A large part of their fruit intake consists of lipid rich fruits in the families Arecaceae, Lauraceae, Meliaceae and Myristicaceae. However, their dietary composition is dependent on seasonal variation in fruit abundance. When fruits are less abundant during dryer seasons they complement their diet with young leaves and flowers, young seeds, bark, honey, decaying wood, and sometimes even termites and caterpillars. Brown spider monkeys forage mainly in emergent trees and upper part of the forest canopy and rely heavily on vision to recognize food items, but also use olfactory, gustatory, and tactile cues to a lesser extent. Figs of different species are a very important food resource, which spider monkeys feed on all year around. They have also been observed eating soil and clay. Several hypotheses to why this might be have been put forward, from the importance of the high mineral content in the soil, to the need for phosphorus and the need to keep an even pH- balance in their digestive system. Spider monkeys also descend to the forest floor to drink water at so called salado sites, and it is hypothesized that their water consumption is a consequence of their high intake of lipid rich fruits. Interspecific feeding competition occurs between spider monkeys and other frugivorous primates, for example woolly monkeys, howler monkeys, squirrel monkeys, and other New World monkeys.

Animal Foods: insects

Plant Foods: leaves; roots and tubers; wood, bark, or stems; fruit; nectar; pollen; flowers

Primary Diet: herbivore (Frugivore )

Studies of seed dispersal by spider monkeys have shown that they play an important role in the maintenance of neotropical rain forest diversity, both through endozoochory and exozoochory. Endozoochory is when the animal disperses the fruit's seeds within the body of the animal, as they swallow the seeds and they pass through the animal's digestive system. Exozoochory is when the animal disperses seeds by carrying them off from the tree to another location and drop them. Link and Di Fiore (2006) found that Ateles belzebuth swallowed 98% of the seeds from the approximately 152 different plant species that the monkeys fed on. They also found that monkeys appear to be particularly important dispersers for plants producing large seeded fruits or those protected by thick husks, many of which other frugivorous species cannot eat. An individual spider monkey dispersed a minimum of 195,000 seeds per year which were bigger than 1 mm in diameter and 35,000 seeds bigger than 3 mm in diameter. The longest distance seeds were moved was 1.2 km, though the average distance was 443 m from the parental source. The results of Link and Di Fiore (2006) and Stevenson and Aldana (2008) show that spider monkeys play a significant role as seed dispersers and that a population decline could have a big and direct impact on forest dynamics, particularly if other disperser species cannot compensate for their lost ecological services. Furthermore, it is possible that their fission–fusion social structure and ranging behavior also influence their pattern of seed dispersal. The fact that they split up in subgroups while foraging could generate a more scattered distribution of defecated seed across the habitat, compared with species that ranges in more cohesive groups. This ranging pattern of spider monkeys could in turn have positive effects on growing rates and survival of the seeds.

Ecosystem Impact: disperses seeds

Mutualist Species:

• Arecaceae
• Lauraceae
• Meliaceae
• Myristicaceae

Because of the large body size of Ateles hybridus, the only significant potential predators on adult individuals are thought to be jaguars and pumas. Matsuda and Izawa (2008) report predation attempts by a jaguar (Panthera onca) and a puma (Puma concolor) on an adult female of the spider monkey species Ateles belzebuth. However, babies and juveniles are susceptible to predators like harpy eagles (Harpia harpyja), crested eagles (Morphnus guianensis), and smaller carnivores.

Poaching also poses a major threat to Ateles hybridus, they are subject to both subsistence and commercial hunting. They are primarily hunted for meat, but hunting for the pet trade is not unusual. In pet trade situations the female is killed and the baby is kept and sold.

Known Predators:

• jaguars (Panthera onca)
• mountain lions (Felis concolor)
• harpy eagles (Harpia harpyja)
• crested eagles (Morphnus guianensis)

Brown spider monkeys frequently use a wide variety of calls to keep contact with each other and to locate other subgroups. They use so called whinnies, i.e. loud calls mostly, which bring information about location and identity of the emitter, but they also use ‘ts chookis’, whoops, wails and screams. The latter can be heard over long distances. Alarm calls are also used when predators are nearby.  Tactile communication occurs in the form of grooming. This is an infrequent behavior in spider monkeys and some claim that it is due to the absent thumb. Ahumada (1992) found that Ateles geoffroyi individuals allocated only 2.5% of their daily activity to grooming, mostly adult females groom their offspring or other juveniles, but male-male grooming occurs as well.  Brown spider monkeys have good eye sight and excellent color vision, which is important for detecting and selecting ripe fruits from unripe ones, but is also used for the detecting predators, as well as for communicating with conspecifics. Visual signals such as head shaking, arm and chest scratching as well as tooth exposure are used in antagonistic and threat situations.  Olfactory behaviors are used in sexual contexts, in which chest-rubbing and pectoral gland sniffing occur. Female spider monkeys also use their over-sized clitoris to deposit drops of urine as scent marks.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: scent marks

Perception Channels: visual ; acoustic

The average life span for spider monkeys is approximately 27 years in the wild. In captivity, on the other hand, they can live to be 10 years old or more.

Average lifespan

Status: wild: 27 years.

Range lifespan

Status: captivity: 40 (high) years.

Average lifespan

Status: wild: 27 years.

Typical lifespan

Status: captivity: 40 (high) years.

The mating system of brown spider monkeys is not well studied, but is most likely similar to that of other members of Atelinae which are polygynandrous, where each individual mates with multiple partners. All copulations are initiated by the female, which indicates a high level of female mate choice and might lead to reduced aggression in males. Females in this genus copulate with many males over a period of time; this might be a female strategy to prevent infanticide by causing paternity confusion. However, intragroup infanticide by other males has been observed, although not reported for this particular species. Mating is not seasonal and no precopulatory rituals have been observed in spider monkeys.

Mating System: polygynandrous (promiscuous)

Similar to the other species of spider monkeys, Ateles hybridus is characterised by a slow reproductive rate, with females usually giving birth to a single offspring every 3 to 4 years. Although not reported for this particular species, intragroup infanticide by males has been observed in other spider monkey species which shortens the interbirth interval. In captivity the birth interval of brown spider monkeys can be reduced to a minimum of 1.5 years and they do not show seasonality in their births. Wild populations, however, show a low grade of seasonality, with a higher birth rate at the beginning of the rainy season, May to July, when fruits are more abundant. The species typically reaches sexual maturity at 4 to 5 years of age and females give birth to their first infant at an age of 7 to 8 years.

Breeding interval: Female brown spider monkeys give birth to a single offspring every 3 to 4 years.

Breeding season: Wild populations, but not captive, show a low grade of seasonality, with a higher birth rate in the beginning of the rainy season, May to July.

Range number of offspring: 1 to 1.

Range gestation period: 226 to 232 days.

Average gestation period: 230 days.

Average birth mass: 450 g.

Range weaning age: 12 to 20 months.

Average weaning age: 15 months.

Average time to independence: 18 months.

Average age at sexual or reproductive maturity (female): 4 to 5 years.

Average age at sexual or reproductive maturity (male): 4 to 5 years.

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

The gestation period is approximately 226 to 232 days. When offspring are born they cling to their mother’s belly the first couple of months, and then climb over to her back. Young lactate at least one year. In captive spider monkeys, however, lactation has been seen up to twenty months. Females provide the major part of the parental care and very strong social bonds are formed between females and their offspring. During the dependent period, which is approximately 18 months, the offspring gets protection as well as an extended period of learning, where the offspring learns everything from social to foraging behaviors.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents; extended period of juvenile learning

Both of the subspecies of Ateles hybridus are listed as Critically Endangered on IUCN Red List and are listed in IUCN's “world’s 25 most endangered primates." The biggest threats to their populations are forest fragmentation and degradation, as well as the pet trade and illegal hunting. Large proportions of A. hybridus habitats have been converted to lands for agriculture and a lot of the remaining habitats are surrounded by human populations and roads. Only 0.67% of their distribution is protected, so there is a urgent need for protected areas and national parks, which also could include two other threatened endemic primates, white footed tamarins (Saguinus leucopus) and woolly monkeys (Lagothrix lugens). As mentioned in the habitat section, A. hybridus prefers continuous, secondary forests, but only 9% of Ateles h. brunneus potential range remains in that condition. The large body size of A. hybridus and their slow reproductive rate, with late maturation and long interbirth intervals, constrain them from recovering from population declines and make them more vulnerable to extinction.

A combination of ex-situ, in-situ, and education projects is necessary to protect this endangered species. To estimate the density and distribution for this species is also a priority research topic for conservation purposes. Protected areas are necessary for their survival as well as breeding programs for captive animals. Also surveys are much needed to establish population densities of some of the subspecies and to determine local threats.

Brown spider monkeys possess all of the natural history characteristics that accompany higher risk of extinction: large body size, slow reproductive rate, being a food specialist, having a large home range, long life span, late maturation, and long interbirth intervals. All this constrains the species from recovering from population declines, and make them more vulnerable to extinction. The large-scale fragmentation and deforestation of rainforest is a direct threat to A.hybridus as secondary forest is unsuitable as habitat for them. A. hybridus inhabit fragmented habitats and we know suprisingly little about the processes that underpin survival in fragmented habitats. Small- population effects might be too serious to be reversed. It would be unfortunate to lose a species that we still know so little about. We have just begun to understand aspects of their behavior and ecology. Further studies would increase our understanding of, for example, their complex social structure and hierarchies.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: critically endangered

There are no known adverse effects of Ateles hybridus on humans.

Brown spider monkeys are critical members of the rainforest ecosystems they live in, they are important for forest regeneration through seed dispersal.