Bolivian Gray Titi, Plecturocebus donacophilus
BOLIVIAN GRAY TITI
Geographic Distribution and Habitat
The Bolivian gray titi (Plecturocebus donacophilus, formerly identified as Callicebus donacophilus), also known as the white-eared titi and the Bolivian titi, is a New World monkey native to the South American countries of Bolivia and Brazil. Its geographic distribution extends from the upper parts of the Mamoré, Río Grande, and San Miguel (Itonomas) river basins east of the Manique River in Beni, Bolivia, to the forests surrounding the major Bolivian city of Santa Cruz de la Sierra, then northward to southern Rondônia in Brazil.
Although Bolivian gray titis can be found in tropical humid forests, they prefer to live in slightly drier habitats. They are common to riparian zones and gallery forests near swampy grasslands and open areas, typically residing in areas of dense vegetation within the thickest part of a forest. The monkeys’ presence in forest remnants within urban areas offers evidence of the species’s tolerance to habitat degradation.
The Bolivian gray titi monkey was previously known by the scientific name, Callicebus donacophilus. However, the diversity among titi monkey species led researchers to divide the genus Callicebus into three distinct genera:
Thus, the Bolivian gray titi monkey was reclassified from the genus Callicebus to a new genus, Plecturocebus, while retaining its species name—thus becoming Plecturocebus donacophilus.
Other titi species within the Plecturocebus genus include:
-Rio Beni titi (Plecturocebus modestus)
-Rio Mayo titi (Plecturocebus oenanthe)
-Ollala brothers’s titi (Plecturocebus olallae)
-White-coated titi (Plecturocebus pallescens)
Size, Weight, and Lifespan
Bolivian gray titis are small New World monkeys, weighing between 1.8 and 2.6 lb (0.8–1.18 kg). Females usually weigh a bit less than males.
Head-to-body length in males averages 12 in (31 cm). Head-to-body length in females averages 13 in (33 cm). A long, fluffy, nonprehensile tail adds another 19–20 in (48–51 cm) to a compact body. Their hind limbs are long.
Apart from the slight difference in body weight and length, there is no distinct sexual dimorphism between the sexes. Sexual dimorphism is distinct differences in size or appearance between the sexes of an animal in addition to differences in their reproductive organs.
Little information is available regarding the lifespan of these monkeys in the wild. Captive Bolivian gray titis, however, are known to live for 25 years.
Erection or bristling of hairs due to the involuntary contraction of small muscles at the base of hair follicles that occurs as a reflexive response of the sympathetic nervous system especially to cold, shock, or fright.
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A plush fur coat nearly overwhelms the body of this titi monkey. Throughout this dense, gray pelage, Nature has used her brush to paint each hair with alternating light and dark bands of orange-brownish flecks. The resulting streaked appearance, known as “agouti,” rivals the high-end coloring process offered by any fancy hair salon. It’s also an important adaptation, scientifically referred to as “cryptic coloration” that allows the monkeys to blend in with their surroundings to help avoid predation.
White tufts of fur decorate the titi’s ears, giving this monkey its alias of white-eared titi. The long, impressive tail is light gray on the underside and darker gray on the topside; it becomes grayer as the monkey ages. A subtle but expressive face, with a barely perceptible underbite, is characterized by a whiskered gray muzzle and brown eyes that assess the world.
Fruits comprise more than 70 percent of the Bolivian gray titi’s diet, making this primate a mostly frugivorous species. Leaves, especially protein-rich young leaves and leaf buds, are also on the menu, followed by seeds. Over 100 species of plants and fruits provide the monkeys’ food sources. Insect entrees and snacks complete their diet. Favored insect meals include ants, moths, butterflies (including their cocoons), and spiders. Small, flying insect prey—with the misfortune of choosing the wrong flight path—are subsequently placed within the titis’ reach, end up as monkey snacks.
Bolivian gray titi monkeys increase their leaf consumption during the dry season, when fruits are scarce. Lactating females increase their insect consumption to increase the protein content of their diet.
Behavior and Lifestyle
Bolivian gray titi monkeys live in small family groups of 2 to 7 members, usually consisting of a bonded adult pair and their young. (Multi-male groups have also been recorded.) Males appear to exert a measure of leadership authority in family groups; however, no obvious dominance hierarchy is apparent between sexes or among individuals, and either member of a bonded pair may follow the other’s lead throughout the day. Adult titi pairs coordinate their daily activities so they can always be physically close to one another. These life-long partners spend little time apart. Should they find themselves separated from one another, they display physical signs of anxiety and distress.
These titis are diurnal (active during daylight hours), and arboreal (they spend their lives in trees, rarely descending to the ground).
Waking at sunrise, Bolivian gray titi monkeys spend their day foraging, eating, and resting. Their day typically consists of a main feeding period in the morning and another in the afternoon, broken up by a midday nap. Naps are necessary so their bodies have the “down time” to digest the cellulose in their largely plant-based diet. These monkeys are active, overall, for about 11.5 hours; nearly 3 hours of this time is spent feeding. They remain active until sunset when they select a tree at least 49 ft (15 m) off the ground to sleep in overnight, close to one another in the vines of small branches. The bonded pair often sleeps with their tails entwined.
They travel mostly through the forest understory quadrupedally (on all four limbs), clambering from branch to branch; their tail never touches the support the monkeys land on. Titis prefer branches that are less than 2 in (5 cm) in diameter. They sometimes take short leaps, no greater than the length of their bodies, between trees where vegetation is not thick enough to support their quadrupedal locomotion. When traveling longer distances, the titis may enter the forest canopy or cross small areas of open ground, though the latter is rare. When traveling on the ground, they use a “bounding movement,” leaping more than 3.3 ft (1 m) off the ground. The titis typically cover between 0.3 and 0.9 mi (0.5–1.5 km) during a day’s travel. Their long hind limbs are well adapted to their movements.
Bolivian gray titi monkeys exhibit little interest in venturing outside of their small home range of 1.24 to 35 ac (0.5–14 ha); in fact, they are wary and hesitant about approaching unfamiliar situations. But they are also territorial when it comes to announcing and defining their turf to outsiders and interlopers. Males, especially, exhibit increased agitation and respond with threatening behavior towards intruding (outsider) males. Should an outsider male approach the female partner of a bonded adult couple in an attempt to woo her, the male partner will grasp and mount his female partner—sending a message to the would-be Lothario to keep away (or rather, no monkeying around with his lady).
Although they share their habitat with other New World monkeys—who include marmosets, tamarins, squirrel monkeys, capuchins, owl monkeys, howler monkeys, woolly monkeys, and spider monkeys—Bolivian titis prefer their own company. They do their best to remain isolated within their social group and try to avoid contact with other primates. This aversion might be because members of larger primate species often chase titi monkeys away from fruit trees and other sources of food.
Bolivian gray titis are, themselves, food sources for certain raptor species—including Guianan crested eagles and ornate hawk eagles. Other predators include felids (wild jungle cats) such as jaguars and various tree-dwelling snakes. Predation on titi infants by tufted capuchins has been observed.
Like all titi monkeys, Bolivian gray titis communicate through a wide variety of vocalizations—often repeated and used in sequence—to indicate distress, conflict, play, bonding, or disturbance, or to claim territory. Researchers have classified their complex calls into two groups: high-pitched quiet calls and low-pitched calls.
High-pitched calls include squeals, trills, chirps, and grunts that the titis sound while foraging, when attempting to locate others members of the group, when they are agitated, or when they should encounter a violent situation.
Low-pitched loud calls include chirrups, moans, pants, honks, bellows, and screams that the titis sound when signaling other social groups over a long distance for the purpose of ensuring adequate spacing between the home ranges of different family groups. The monkeys use certain chirrup sounds to locate group members; these calls may reveal information about the age and sex of the monkey emitting the call. Moans are heard during copulation and when greeting another group member.
Bolivian gray titis also use vocalizations to define and reinforce the borders of their home range. Soon after awaking each morning, Bolivian gray titis perform a bout of vocalizations consisting of loud calls, moans, grunts, and other calls at the outer boundary of their territory. A group’s male initiates these calls.
If a neighboring titi group is in the vicinity, the two groups engage in “duetting,” each calling out to the other. As the groups approach one another, the intensity of their duetting increases, with both males and females participating. Should they directly confront one another, the titis attempt intimidation through tail lashing, piloerection, and chasing one another.
Physical communication is used for more than intimidation, however. As with most nonhuman primates, grooming is an important daily activity for titis that helps to establish social bonds. A behavior that wildlife researchers have dubbed “tail twining” or “tail entwining” seems to foster a sense of comfort, or intimacy, between these monkeys. This behavior is especially prevalent between a bonded adult couple. Perched side by side on a branch with their long tails interwoven (entwined), and their hands clasped, it’s easy to imagine their deep affection for one another. Further evidence of this affection includes nuzzling and lip smacking.
Bolivian gray titis, like all titi monkeys, are monogamous; they mate for life.
Breeding season is thought to be in the spring, preceding Bolivia’s rainy season. In captivity, Bolivian titi monkeys breed throughout the year. Captive female titi monkeys give birth approximately one year after selecting a mate.
Although female titi monkeys reach sexual maturity at 2 years of age, they don’t usually reproduce until 4 years of age. After a gestation period of about 18 weeks, they give birth to a single offspring (twins are rare) and typically give birth to one infant each year.
Nature dictates that mothers nurse their babies, but titi mothers invest little maternal care beyond this biological act. Although titi babies need to be carried their first few months of life, their mothers carry them only for their first week of life, and only about 20 percent of the time. After that, titi mothers seem to abandon direct care of their offspring.
Fathers are the primary caregivers; they are the ones who carry and protect their young. So, it’s no wonder that infants form an emotional attachment to their dads. Wildlife researchers report that infant titis experience more stress and elevated heart rates when separated from their fathers than when separated from their mothers. While the infant-father bond is strong, Bolivian gray titis experience a stronger bond with their mate than with their offspring.
Between 2 and 4 years of age, young titis strike out on their own; females leave their birth group earlier than males.
Thanks to their largely frugivorous diet, Bolivian gray titi monkeys help to regenerate their forest habitat by dispersing seeds via their feces, thereby encouraging new plant growth.
Despite declining populations, Bolivian gray titi monkeys are listed as Least Concern by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. Rationale for this lackluster classification may be due to the species’s wide range and adaptability to degraded habitat; Bolivian gray titi monkeys survive within the city limits of Santa Cruz de la Sierra and on the borders of rural human establishments. They have few natural predators. The main threat against them is deforestation and habitat loss due to agriculture.
The Bolivian gray titi is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
Although the titis are able to survive in degraded habitat, these fragmented patches prevent the monkeys from establishing new territories and decrease their reproductive opportunities. To help ensure the species’s propagation, and survival, conservationists have proposed that forest corridors be built to connect fragmented forest habitats.
Those Bolivian gray titi monkeys living within Bolivia’s Beni Biological Station Biosphere Reserve and Amboro National Park are afforded the protections offered by these reserves.
Written by Kathleen Downey, February 2019