Trachypithecus phayrei
Phayre's leaf monkey

Phayre's leaf monkeys, Trachypithecus phayrei, range from Eastern India to Southern China, including portions of Thailand and Vietnam. ("Phayre's Leaf-monkey", 2011; Bhattacharya and Chakraborty, 1990)

Phayre’s leaf monkeys, Trachypithecus phayrei, are found in a variety of habitats due to human disturbance within its range. They often reside in mixed evergreen/deciduous primary and secondary forests. In thick evergreen forests, Phayre’s leaf monkeys can be found 15 to 50 m above the ground. In areas lacking these primary and secondary forests,this species depend on bamboo and small shrubs. Phayre's leaf monkeys may also be found along stream banks containing thick bamboo forests. ("Phayre's Leaf-monkey", 2011; Bose, 2003)

The three subspecies of Phayre's leaf monkeys, T. p. phayrei, T. p. crepusculus and T. p. shanicus are slightly different in coloration. In genral, Phayre’s leaf monkeys are dark grey-blue in color with some brown on the dorsal side and have mostly brownish-white pelage on the ventral side. The upper arms, legs, and tail are silvery-grey in color, and, in general, the head and tail are darker than the rest of the torso. The area around the lips and eyes are white. Young Phayre’s leaf monkeys exhibit yellowish colored fur until about 3 months of age when the pelage begins to change. Adult Phayre's leaf monkeys also have slightly longer hair on the top of their head. ("Phayre's Leaf-monkey", 2011)

Female Phayre's leaf monkeys are slightly larger than males. Whereas males range from 1.07 to 1.1 m in length, females range from 1.15 to 1.3 m. The tail of Phayre's leaf monkeys constitutes 68 % of the overall length, ranging from 65 to 86 cm. Males weigh an average of 7.4 kg and females an average of 6.2 kg. Male Phayre's leaf monkeys can be distinguished from females in the field is by observing differences between ocular markings. In males, the white ocular rings around the eyes are parallel to the side of the nose, resulting in a black strip uniform in width. In females, the white ocular rings around the eyes bend inwards toward the nose causing more of black triangular shape. (Bhattacharya and Chakraborty, 1990)

The mating system of Phayre’s leaf monkeys is similar to that of spectacled langurs Trachypithecus obscurus. Troops of Phayre’s leaf monkeys have one dominant male that breeds with multiple females. Because adolescent males leave the troop before reaching sexual maturity, males do not challenge the dominant male of or mate with females within their natal group. Outcast males may join other solitary males, becoming nomadic in search of breeding females or the opportunity to challenge a dominant male in order to establish his own troop. Dominant males protect their territory from troopless males. If an intruding male wins an encounter, the dominant male is then outcast, and the newcomer gains breeding rights. The new dominant male may kill young from the previous male, effectively permitting earlier copulation with females. ("Langurs and Leaf Monkeys", 2009; Yeager and Kirkpatrick, 1998)

Breeding of Phayre's leaf monkeys can be intermittent, and births generally occur in March and April. The gestation period from conception to birth is approximately 205 days. Females give birth to one offspring at a time, which nurse for almost a year. Males reach sexual maturity at 3 to 4 years of age. ("Phayre's Leaf-monkey", 2011; Larney, et al., 2007)

Phayre's leaf monkeys invest considerable energy in raising their young. Newborns nurse for almost a year, which greatly increases chance of survival. Mothers are the main caregivers as they feed, protect and groom newborns. It is not uncommon for older female siblings of a newborn to provide minimal care in the absence of the mother. Adolescent Phayre's leaf monkeys tend to keep some contact with their mothers, even after she gives birth to additional offspring. When young Phayre's leaf monkeys fall to the ground, they call out in distress to their mother. In most instances, the mother or an older sibling descend to retrieve it. In the case that an infant is lost from the troop the mother will give a "lost call" in hopes of locating the lost newborn. ("Langurs and Leaf Monkeys", 2009; Larney, et al., 2007)

Little information is known regarding the lifespan of the Phayre’s leaf monkeys. Other species within the family Cercopithecidae have life spans of 20 to 30 years in the wild. (Johnson, 2008)

Phayre's leaf monkeys are very shy and typically flee when threatened. They spend over 75% of their time feeding within tree tops. This speices rarely leaves the safety of the trees, leaving only if their requirements are not met or to negotiate gaps in the canopy. Phayre's leaf monkeys are strongly territorial against other groups of the same species, although sympatric groups of other species may share the same territory. ("Langurs and Leaf Monkeys", 2009; "Phayre's Leaf-monkey", 2011)

Group of Phayre's leaf monkeys vary in size from 8 to 22 members. One dominant male rules the group, composed of 3 to 6 adult females, and a mixture of sub-adults, juveniles, and infants. Females tend to be closely related to each other and rarely leave the troop. Their roles and level of dominance amongst females are not clearly defined. Adolescent males leave the troop at about 3 years of age before they reach sexual maturity, preventing males from challenging the dominant male of or mating with females e within their natal group. Outcast males may join other solitary males, becoming nomadic in search of breeding females or the opportunity to challenge a dominant male in order to establish his own troop. Dominant males protect their territory from troopless males. If an intruding male wins an encounter, the dominant male is then outcast, and the newcomer gains breeding rights. ("Langurs and Leaf Monkeys", 2009; "Phayre's Leaf-monkey", 2011; Yeager and Kirkpatrick, 1998)

Phayre's leaf monkeys have home ranges from 10 to 100 ha, with very little overlap among groups. The size of the range depends heavily on the distribution and abundance of food. If food resources are limited, larger groups will increase the size of their home range in search of food. Although range is mainly determined by group size, group size is heavily limited by social stress. Stress limits population size and thus home range in three ways: stress reduces a female’s ability to conceive and carry an infant to term; stress can lead to immunosuppression making individuals more susceptible to disease and therefore death; and stressed Phayre’s leaf monkeys may disperse, leaving their group, which puts them at a greater risk of death. ("Langurs and Leaf Monkeys", 2009; Yeager and Kirkpatrick, 1998)

Both male and female Phayre's leaf monkeys use vocal calls for a variety of reasons. Adult males use a loud "kah kah kah" call when alarmed. A softer "whoo" call is used when adult males detect a predator within the area. The "cheng-kong" call is emitted by the dominant male to bring the group together. When a dominant male must defend its territory, a "loud call" is used, which is a high pitched roar against intruders. Young Phayre's leaf monkeys will emit a distress call when they fall from the treetops. Femals also use a “lost call” in an attempt to locate lost newborns. This call has also been heard from Phayre's leaf monkeys in the presence of deceased newborns. ("Phayre's Leaf-monkey", 2011)

Phayre’s leaf monkeys are folivores, eating primarily leaves. They have been know to eat leaves from approximately 80 different species of plants. Due to the considerable about of leaves in their diet, Phayre's leaf monkeys have highly adapted stomachs, necessary to digest cellulose and denature the toxins found in leafy materials. Phayre's leaf monkeys also eat bamboo shoots when tree foliage is not as abundant. ("Langurs and Leaf Monkeys", 2009; "Phayre's Leaf-monkey", 2011)

The main predators of Phayre’s leaf monkeys are humans. Native tribes within their ranges, hunt this species for meat. Because the gall stones of Phayre’s leaf monkeys are used for medicinal reasons, poaching by humans is also a threat, particularly around salt springs. Newborns may also be vulnerable to large tree snakes and raptors which are a threat to similar species, though no data on actual predation rates are readily available for T. phayrei. ("Langurs and Leaf Monkeys", 2009; "Phayre's Leaf-monkey", 2011)

As consumers of fruits, Phayre's leaf monkies, Trachypithecus phayrei, may play a role in seed dispersal. The considerable consumption of foliage by this species may also influence plant composition in local ecosystems. ("Langurs and Leaf Monkeys", 2009; "Phayre's Leaf-monkey", 2011; Bose, 2003)

Phayre’s leaf monkeys are hunted for food by local tribes of humans. They are also poached for their gall stones, which are used for medicinal purposes. ("Langurs and Leaf Monkeys", 2009; Bose, 2003)

Conservation efforts have limited slash and burn cultivation and have led to increased protected land, which some would consider as adverse effects toward humans. Local bush hunting is also decreasing as conservation efforts increase. ("Langurs and Leaf Monkeys", 2009; Bose, 2003)

Habitat loss and fragmentation are the biggest threats to the continued survival for Phayre’s leaf monkeys. With isolated populations scattered throughout their range, the viability of these populations is currently unknown. It is estimated that 1,300 individuals currently exist in the wild. (Bose, 2003; Larney, et al., 2007)