Yellow-tailed woolly monkey

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Common name: yellow-tailed woolly monkey
Latin: Oreonax flavicauda’
Genus: Oreonax
Species: flavicauda
Suborder: Haplorrhini
Infraorder:  Simiiformes
Family:  Atelidae
Subfamily:  Atelinae

Life Span:  Unknown
Total Population:  Unknown
Regions:  Peru
Height:  20.3 to 21.1 in
Height (metric) 51.5 to 53.5 cm
Weight:  22.0 lb
Weight (metric): 10 kg
Gestation:  Unknown

Other names: O. flavicaudaLagothrix flavicaudaLagothrix hendeei, Peruvian yellow-tailed woolly monkey, yellow-tailed woolly monkey, Hendee’s woolly monkey; hendees uldabe (Danish); geelstaartwolaap (Dutch); harmaavillaapina (Finnish); singe laineux à queue jaune (French); gelbschwanzwollaffe (German); lagotrice a coda gialla (Italian); barrigudo andino, choro cola amarilla, maquisapa chusco (Spanish); gulsvansad ullapa, hendees ullapa (Swedish).

O. flavicaudais is monotypic, that is, the only member of the genus Oreonax(Groves 2001; 2005). Groves (2001; 2005) moved the Peruvian yellow-tailed woolly monkey (Oreonax flavicauda) to its own genus (Oreonax) from Lagothrix based on cladistic and morphological grounds. However, the idea of the yellow-tailed woolly monkey in a genus separate from the other woolly monkeys is not a new one and was proposed in the early 20th century on grounds of differences in tooth morphology (Thomas 1927). Some authors disagree with Groves’ taxonomic move, and the validity of the genus Oreonax is still debated (Matthews & Rosenberger 2008; Rosenberger & Matthews 2008; Cornejo et al. 2009). For the sake of this factsheet and in recognizance of disagreements over this taxonomic arrangement, Groves (2001; 2005) is followed but the reader is referred to the Lagothrix factsheet for similar species.

As it is among the least known of the primates, data on many aspects of the yellow-tailed woolly monkey behavioral ecology and biology are scarce (Shanee et al. 2007a; Cornejo et al. 2009). Where data is lacking, the reader is referred to the woolly monkey factsheet (Lagothrix sp.) due to presumable similarities between the species.

(Newer information and photos on this species appear at “New population (and new hope) for Critically Endangered Peruvian primate”  by Christopher A. Schmitt, 25th October 2019. This content is provided as a courtesy to PIN readers and is not part of the original peer-reviewed 2005 fact sheet.  jsl Aug. 26, 2021)


Yellow-tailed woolly monkeys are large and robust, with thick, woolly fur, a hairy face and a prehensile tail with a hairless patch on the underside (Leo Luna 1987; Ramirez 1988; Ankel-Simons 2007). Their fur is somewhat longer and denser than the other woolly monkeys (Lagothrix sp.) (Mittermeier et al. 1977; Aquino & Encarnación 1994). They are deep mahogany or copper, darker towards the upper body and head where it is nearly black, with a whitish patch around the mouth, extending from the chin to between the eyes (Fooden 1963; Mittermeier et al. 1977; Leo Luna 1987; Ramirez 1988). Males are somewhat darker in color than females (DeLuycker 2007). The ends of the extremities are nearly black (Leo Luna 1987). There is some red-auburn coloration on the lower back and tail and the belly has long dark-brown fur (Aquino & Encarnacón 1994). The characteristic feature of the species (and the one which gives the species its name) is the yellowish pelage of the inside end of the last third of the tail (Fooden 1963; Mittermeier et al. 1977; Ramirez 1988; Aquino & Encarnacón 1994). This coloration is not present in infants and juveniles (DeLuycker 2007). Also separating it morphologically from the other woolly monkeys are its prominent and long yellowish pubic hair tuft (more prominent in males) and certain distinctive skull and deciduous dentition characteristics (Thomas 1927; Fooden 1963; Mittermeier et al. 1977; Ramirez 1988; Aquino & Encarnacón 1994).

Several museum specimens had an adult head and body length ranging from 51.5 to 53.5 cm (20.3 to 21.1 in), and the tail was somewhat longer than the head and body length (Mittermeier et al. 1977).

The only body weight figure available for yellow-tailed woolly monkeys is around 10 kg (22.0 lb), and is only a rough, unsexed estimate (Leo Luna 1984 cited in Di Fiore & Campbell 2007; Di Fiore & Campbell 2007). True body weight is likely close to that of the genus Lagothrix (Ramirez 1988).

Yellow-tailed woolly monkeys spend almost all of their time in trees, and the tail is used for balance during movement (Ankel-Simons 2007). They can leap as far as 15 m (49.2 ft) (Butchart et al. 1995).


The yellow-tailed woolly monkey is the largest primate endemic to Peru. The distribution of the species is both small and fragmented, occurring only in humid montane forests on the northeastern slopes of the Andes Mountains (Butchart et al. 1995; DeLuycker 2007; Shanee et al. 2007a; Cornejo et al. 2009). The species is restricted to the western Amazonas Department and the eastern San Martín Departments of northern Peru, south and east of the Marañón River, as well as past and possible occurrence in restricted areas within the Cajamarca, Huanuco, Loreto and La Libertad Departments (; Graves & O’Neill 1980; Parker & Barkley 1981; Leo Luna 1982a; Aquino & Encarnación 1994; Butchart et al. 1995; review in Shanee et al. 2007a; Shanee et al. 2007a; Cornejo et al. 2009).


Yellow-tailed woolly monkeys are only found in primary tropical and subtropical premontane, montane, and montane cloud forests (Graves & O’Neill 1980; Butchart et al. 1995; DeLuycker 2007; Cornejo et al. 2009). It is found between altitudes of 1500 and 2700 meters above sea level and its habitat is generally difficult as it is mountainous, steep, rugged, and foggy with many gorges and ravines (Leo Luna 1980; 1982; DeLuycker 2007; Shanee et al. 2007a; Cornejo et al. 2009). The height of the canopy is usually around 20-25 meters above the ground with thick ground-level vegetation (Shanee et al. 2007a). Within the altitudinal range, there are often a number of microclimates, resulting in a large potential temperature range within which the species lives. For example, at one yellow-tailed woolly monkey habitat at Yambrasbamba, Peru, the temperature ranged from a low of 8˚C (46.4˚F) to a high of 25˚C (77.0˚F) (Leo Luna 1980). There is a somewhat dry season between March and September and a particularly wet season between November and February (Leo Luna 1980; 1982).


Knowledge of the ecology of the yellow-tailed woolly monkey is incomplete (Carnejo et al. 2009). The species is predominantly herbivorous, consuming mostly fruits and flowers, particularly of the genera Cecropia (nettles) and Ficus (figs) (Leo Luna 1980; 1987; DeLuycker 2007). They sometimes eat insects (Leo Luna 1987; DeLuycker 2007). Other recorded dietary items include lichens, leaves, buds, bulbs, epiphyte roots and petioles (Leo Luna 1980; 1987; Butchart et al 1995).

Yellow-tailed woolly monkeys are generally inactive (Leo Luna 1982a).

In lower altitudes, yellow-tailed woolly monkeys may be sympatric with white-bellied spider monkeys (Ateles belzebuth), white-fronted capuchins (Cebus albifrons) and night monkeys (Aotus sp.) (Leo Luna 1987). White-bellied spider monkeys have been seen associating and traveling with yellow-tailed woolly monkeys (Shanee et al. 2007b).

A potential predator is the puma (Felis concolor) and raptors elicit alarm calls (Leo Luna 1980; DeLuycker 2007).

Conservation status: please search the IUCN Red List.


In general, group size is usually between around 5 to 18 individuals, but groups as large as 30 have been reported (Leo Luna 1980; 1987; Aquino & Encarnación 1994; Butchart et al. 1995; Mittermeier et al. 1977; DeLuycker 2007; Shanee et al. 2007b; Cornejo et al. 2009). Larger groups could possibly be the result of insufficient habitat or seasonal aggregations of individuals (DeLuycker 2007). Groups are typically multi-male/multi-female, and usually contain more than one adult male (one of which appears to be dominant), and several adult females and subadults (Leo Luna 1980; 1987; Parker & Barkley 1981; Aquino & Encarnación 1994). The social organization is possibly fission-fusion (Cornejo 2008). Similarly to the other woolly monkeys (Lagothrix sp.), yellow-tailed woolly monkey groups will split into subgroups for up to several days at a time (Cornejo 2008). A single group had a home range of 0.69 km² (0.27 mi²) and a daily path of under one kilometer (<0.62 mi) (Cornejo 2008).


Very few data exist about reproduction and parental care in yellow-tailed woolly monkeys. They probably have a low birth rate similar to the genus Lagothrix (around 3 years) (Leo Luna 1980; DeLuycker 2007). They may reach sexual maturity when they are older than four years of age, but this has not been demonstrated (Leo Luna 1980).

Juvenile and infant yellow-tailed woolly monkeys do not have the characteristic yellow tail-hairs nor the genital tufts of adult individuals (Thomas 1926; Leo Luna 1982b cited in DeLuycker 2007; DeLuycker 2007).

Males have been seen carrying infants ventrally, while a female was seen carrying a young juvenile on her back (Parker & Barkley 1981; Butchart et al. 1995).


When excited, a bark is emitted and can be heard for some distance (Leo Luna 1980). Alarm calls are emitted in response to potential predators, including raptors (DeLuycker 2007). Adults have been heard calling for prolonged periods of time (ca. 30 mins) (DeLuycker 2007).

When confronted with a threat, male yellow-tailed woolly monkeys will confront the threat with a display which includes showing of the genitals, hip shaking, shaking and throwing tree branches, and occasionally urination and defecation (Leo Luna 1980; 1982a; Butchart et al. 1995; DeLuycker 2007). “Simulated attacks” are also directed at threats sometimes, where the woolly monkey will run and quickly leap into supports above the threat (Leo Luna 1982a).


For individual primate species conservation status, please search the IUCN Red List.
Also search the current scientific literature for primate conservation status (overall as well as for individual species), and visit CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora).

Conservation information last updated in 2009 follows, for comparison:

The yellow-tailed woolly monkey is one of the World’s 25 Most Endangered Primates (Cornejo et al. 2009; Mittermeier et al. 2009). Until the middle of the 20th Century, most of the yellow-tailed woolly monkey’s habitat was largely inaccessible. Since then, road building to increase human habitation of their region of occurrence has increased threats to the species (Leo Luna 1982; 1987). Large-scale immigration started during unrest in the 1970s and 1980s, and the influx continues today (Shanee et al. 2008; DeLuycker 2007). There are no up-to-date population estimates but its total area of potential suitable habitat is under 8,000 km² and is declining and largely fragmented (Cornejo et al. 2009). The species is known to exist in several protected areas, but even these areas are being illegally logged and hunted, with a lack of law enforcement, and have increasing human populations (Cornejo et al. 2009). Further, the low birth rate exacerbates these threats because populations are slow to recover, particularly from hunting (Leo Luna 1980; 1987). Other aspects of its ecology that increase the susceptibility of the species include its low density and limited range of occurrence (Leo Luna 1987).


Threat: Human-Induced Habitat Loss and Degradation

The primary threat to the yellow-tailed woolly monkey is habitat loss or fragmentation through clear-cutting or selective logging of its forest habitat (Leo Luna 1982; 1987; Butchart et al. 1995; DeLuycker 2007; Cornejo et al. 2009). Deforestation is intensified and increased by continuing human immigration into suitable habitats (DeLuycker 2007; Shanee et al. 2007a). Areas are cleared for various types of agriculture, including coca cultivation and coffee cultivation, but also for timber, mining, road construction, and cattle husbandry (DeLuycker 2007; Shanee et al. 2008). Soils are poor, and quickly erode, necessitating further clearance (Shanee et al. 2008). Such destruction is often illegal and sometimes occurs in protected areas (DeLuycker 2007).

Threat: Harvesting (hunting/gathering)

Hunting is another major threat to the survival of the species (Leo Luna 1987; Shanee et al. 2007a). Yellow-tailed woolly monkeys are often hunted for food and trade, for both indigenous and immigrant subsistence (Parker & Barkley 1981; Leo Luna 1987; Shanee et al. 2007a). They are easily hunted due to their large size and their loud and obvious responses to intruders, making them easy to find for hunters (Butchart et al. 1995; DeLuycker 2007). Mothers are sometimes shot to procure their infants as pets (DeLuycker 2007). These infants are either kept or sold for approximately 10-70 US dollars (Shanee et al. 2007a).


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