Vieira’s titi, Plecturocebus vieirai
VIEIRA'S TITI
Plecturocebus vieirai
Geographic Distribution and Habitat
Vieira’s titi monkeys are native to Brazil, residing in the country’s north-central region within the states of Mato Grosso and Pará. Their geographic distribution encompasses the areas west of the Xingu River, south of the Iriri River, east of the Iriri and Teles Pires Rivers, southward to the headwaters of the Xingu and Teles Pires Rivers, and stretches to the border between the Amazonia–Cerrado biomes of northern Mato Grosso and south-central Pará.
Amazonia’s ecosystem, defined by the Amazon River basin, is characterized by floodplain forests and várzea, areas alongside rivers prone to flooding during the rainy season, flooded igapo or “root” forests that border blackwater rivers, and terra firma forests, situated on firm, dry land.
Cerrado’s ecosystem biome is characterized by forest savanna, wooded savanna, grasslands, wetlands, and gallery forests—an area known as the Brazilian highlands, or “Planalto.”
It is within mature, secondary, and degraded Amazonia and Amazonia-Cerrado transition forests that Vieira’s titi monkeys are found. The titis also inhabit areas alongside river tributaries or canals, known as igarapé, where moriche palm trees grow. They dwell at elevations from 656 to 1,214 feet (200 to 370 meters).
Discovered in 2012, the Vieira’s titi monkey belongs to the primate family Pitheciidae and to the subfamily Callicebinae. Based on molecular, morphological, and biogeographic evidence, this subfamily is composed of three genera: Callicebus of the Atlantic Forest; Cheracebus of the Orinoco, Negro, and upper Amazon basins; and Plecturocebus of north-central Brazil, the Amazon basin, and Chaco in northwest Paraguay. As one of the species in the genus Plecturocebus, Vieira’s titi monkeys are considered part of the eastern Amazon clade of the so-called moloch group, along with the Prince Bernhard’s titi monkey (Plecturocebus bernhardi) and the red-bellied titi monkey (P. moloch). Vieira’s is one of at least 34 known titi species.
Size, Weight, and Lifespan
Little sexual dimorphism, or difference in appearance, aside from genitals, is shown in this species, considered a small-to-medium-sized primate with longer forelimbs than hindlimbs. Head-to-body length is from 11 to 17 inches (30 to 45 cm), with an average length of 12 inches (30.5 cm). The tail is longer than the body, adding another 16 to 20 inches (41 to 51 cm) to the monkey’s frame. Average weight is just over 2 pounds (0.95 kg).
Lifespan for Vieira’s titi monkeys has not been documented. For a clue, we might look to the two other members of the moloch group. Both red-bellied titis and Prince Bernhard’s titi monkeys live into their 20s.
Appearance
It’s easy to think of a child’s plush toy when you look at this titi monkey, whose stocky body is cloaked in a thick, grizzled, mostly gray fur coat with muted rust-colored flecks, a pattern known as “agouti”. The chest, abdomen, and inner side of arms and legs are covered with fluffy, pale-orange fur, giving contrast to the overall pelage or fur coat. The upper side of the hands, feet, and tip of the tail are furred in white. Vieira’s black, hairless face is surrounded by a white ruff that defines its brow ridge with a slight, furry poof that meets the titi’s grizzled, gray crown. Ears are neatly and symmetrically placed and scarcely visible amidst all that fur. Deep brown eyes that assess the monkey’s surroundings sit above a flattened muzzle characterized by evenly spaced, flared nostrils that breathe in the scents of the forest. Light-colored whiskers randomly stem from the facial skin above the Vieira’s titi monkey’s narrow lips.
Diet
Titi monkeys are herbivores with a frugivorous predilection; which is a super-science-y way of saying they eat primarily plant foods and have a strong preference for fruits. Some titi species are reported to eat up to 100 types of fruits! Figs, berries, and other tropical fruits are on the menu, along with leaves, flowers, and the occasional insect. As to the dietary proclivities specific to Vieira’s titi monkeys, scant information is available. Again, we must look to the other two moloch group members to make our informed assumptions.
Red-bellied titi monkeys eat lots of fruits, of course. But leaves and a generous helping of spiders, ants, and moths complement their meal plan. Prince Bernhard’s titi monkeys are especially fond of fruits from the Oenocarpus distichus and Orbignya phalerata plants, two types of palm trees; along with leaves and fruits of the Inga plant, a type of shrub; and various lianas, long-stemmed woody vines that grow on trees.
Certain Cheracebus titi species, known to share habitat with Vieira’s titi monkeys, exhibit their own dietary predilections. While the moloch group members are reported to eat more leaves, their Cheracebus titi cousins consume more insects, seeds, and tough-skinned fruits.
Behavior and Lifestyle
Because few studies have been conducted on this species, other titis in the genus Plecturocebus provide us with clues on behavior and lifestyle. Like other titi monkey species, we know that Vieira’s titi monkeys are arboreal; that is, they spend most of their time in the trees, favoring the dense vegetation of the forest understory, and rarely descend to the forest floor. They are active during daylight hours, making them diurnal.
So what do titi monkeys do all day? An adult paired titi couple begins the day at dawn by performing a duet. Then the entire family group leaves their sleeping tree to forage together, traveling travel through the lower levels of the forest quadrupedally (using all four limbs), at times exercising short leaps between trees. Their long nonprehensile tail, while incapable of grasping, assists with balance and helps them to stick their landings. A noontime nap breaks up their day of foraging and feeding.
Overnight, titi monkeys sleep together, with tails intertwined, in vine-encrusted trees that help conceal them from would-be predators. Raptors pose the greatest predator threat and include harpy eagles (Harpia harpyia), ornate hawk-eagles (Spizaetus ornatus), and Guianan crested eagles (Morphnus guianensis). Other predators include wild cats, snakes, and, potentially, capuchin monkeys (Cebinae). Viera’s titis often return to the safety of the same “sleeping tree” each night.
While aggressive predator avoidance strategies have not been observed or reported in Vieira’s titis, wildlife biologists have documented such in red titi monkeys (Plecturocebus cupreus). In response to a threat from an ocelot (Leopardus pardalis) and a Boa constrictor, red titis mobbed the offending predators. Active predator mobbing is also known to occur with black-fronted titi monkeys (Callicebus nigrifrons).
The origin of the word “titi” is from the Aymaran language, spoken by the indigenous people of the Bolivian Andes, meaning “little cat.”
Plecturocebus vieirai is named after Professor Carlos Octaviano da Cunha Vieira (1897-1958), a Brazilian mammal researcher and former curator of the Mammal Collection of the Zoological Museum of the University of São Paulo (MZUSP), Brazil.
Vieira’s titi monkeys live in small family groups consisting of a mated adult pair and their offspring, usually no more than four individuals in total. Unlike many primate species, titis do not appear to be constrained by a social hierarchy. Individuals are friendly and social with other members within a group. A mated pair is particularly affectionate with one another. But Vieira’s titis do not lay out the welcome mat for outsiders; the species is highly territorial.
Should they run into titis from outside groups, which is not uncommon while out foraging, Vieira’s titis vociferously defend the borders of their home range. A cacophony of calls, intended to intimidate, ensues between the two groups. Physical altercations are rare, and the two groups most often retreat deeper into their respective territories.
While home range size is not recorded for Vieira’s titis, the average size for other titis in the genus Plecturocebus is a mere 0.002 square mile (0.005 square km)—or less. The monkeys cover about 1,394 to 3,780 feet (425 to 1,152 meters) in their daily travels.
In addition to other titi monkeys, wildlife species who share habitat with Vieira’s include giant anteaters (Myrmecophaga tridactyla), giant armadillos (Priodontes maximus), jaguars (Panthera onca), ocelots (Leopardus pardalis), pumas (Puma concolor), marsh deer (Blastocerus dichotomus), maned wolves (Chrysocyon brachyurus), black spider monkeys (Ateles paniscus), howler monkeys (Alouatta), poison dart frogs (Dendrobatidae), and several species of sloths. Hundreds of bird species—not just birds of prey—live here, too, like the stunningly beautiful hyacinth macaw (Anodorhynchus hyacinthinus), who has the distinction as the largest flying parrot species.
Vocalizations are an important method of communication for titi monkeys, and the Vieira’s are no exception. Aside from a paired couple’s morning duet and a group’s loud and raucous warning calls to outsiders to stay away, a wide range of other calls are used in various situations. Alarm calls are sounded in response to a predator threat, and the monkeys may call out to one another while out foraging (so-called “location calls”). Or they may simply engage in conversation while hanging out in the trees. Their loud chorus can sound like a breathless, whimpering puppy whose whimpers reach a crescendo. Throw in some “hoots” and “quacks” and you have quite a textured, complex dialogue. Infant calls are described as “trills,” whereas adult titi calls are described as “chirps.” For those titis held in captivity for behavioral research purposes, scientists have observed “isolation peeps” in the confined primates.
Scent marking is another method that titis use to convey certain messages, e.g., to mark territorial boundaries or to send an intimate message to a fellow group member. The “chest rub” also serves as a visual clue where adults stimulate secretions from large glands in their chest. They first slowly and (dare we say?) dramatically draw tree branches across their chest, and then either rub their chest with their hands in a downward motion or lean against a tree limb or other surface to cause friction that, in turn, releases the secretions.
Allogrooming (mutual grooming sessions) helps to strengthen social bonds, as does tail twining (described as being akin to human primates holding hands with one another).
Repeated and rapid opening and closing of the mouth has been observed in those titi monkeys confined for behavioral research, as has back arching, tail lashing (vigorously swinging the tail side to side), and piloerection of hairs on the tail.
Like other titi monkey species, Vieira’s titis are monogamous; that is, an adult male and female engage in an exclusive, intimate (sexual) relationship. Bonded titi pairs show great devotion to one another.
Titi monkeys attain sexual maturity (when they are able to reproduce) by the age of 2, though females do not menstruate or exhibit swelling in their external genitalia when in estrus (the period of sexual receptivity, informally referred to as “in heat”). Another curiosity concerns mature female offspring who, for whatever reason, remain with their family group rather than venturing out on their own. These “don’t want to leave home” females will never breed, nor show signs of sexual activity, so long as they stay with mom and dad.
After a gestation period of about 5 months, a female gives birth to a single infant; twins are rare. Births can occur year-round, though most often during the rainy season (December to May) when fruits are abundant. The normal interbirth interval is one year; if, however, an infant dies before she is weaned, the interbirth interval is significantly shorter for the lactating female. Apart from mothers nursing their newborns, fathers are the primary caregivers for a couple’s offspring. Infants are considered weaned at 8 months old, at which time fathers begin to share solid foods with their young titi offspring. Youngsters typically clamber aboard dad’s back so that he can carry them around.
Like so many other frugivorous (fruit-eating) primates, Vieira’s titi monkeys help to regenerate their forest habitat by distributing the seeds of the many fruits they eat, via their feces, in the course of their daily travels.
The Vieira’s titi monkey is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN, March 2022), appearing on the IUCN Red List of Threatened Species. Various anthropogenic (human-caused) activities have pushed the species to the brink of extinction.
The swath of land that Vieira’s titi monkeys precariously inhabit is known as the “Amazonian Arc of Deforestation,” ignominiously named for its devastating habitat loss. Large expanses of forest have been razed and logged and the land transformed into agricultural tracts for growing crops, cattle ranching, and for human settlements with related infrastructure such as roadways, railroads, and hydroelectric plants.
Human-driven climate change further threatens the species. Even those Vieira’s titis residing within protected areas of the species’ northern range on indigenous lands cannot escape the disastrous impact. Greenhouse gas emissions are causing extended dry seasons, increased frequencies of droughts and forest fires, and dramatic reductions in rainfall—collectively and dangerously disrupting the natural ecosystem.
Researchers predict that by 2044, as little as 14 percent of Vieira’s natural habitat could remain.
The Vieira’s titi monkey 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.
Wildlife biologists have called the species an “emblematic example” for discussing the challenges of biodiversity conservation and climate change mitigation in one of the world’s largest deforestation frontiers and hotspots. As such, they call for serious investment into research concerning the vital role that these primates play in keeping the Amazonian ecosystem healthy. They further assert that protecting habitats within the Arc of Deforestation will save not only the Vieira’s titi monkeys from extinction but will also protect other endemic species and positively influence biodiversity conservation locally, regionally, and globally.
Primate watching, as a form of ecotourism, has been suggested as a profitable and sustainable alternative to the current detrimental anthropogenic activities that overexploit natural resources. The activity has the potential to reduce habitat loss, mitigate climate change, and provide an alternate source of income for native people who are forced into complicity in ravaging the environment that supports them—by powerful, criminal landowners who have acquired huge tracts of forest in illegal “land grabs.”
But protecting this naturally verdant region and the wildlife species who make their home here—many who are found nowhere else in the world—is too complicated to be addressed solely by ecotourism. Wildlife biologists advocate for the creation of additional protected areas and the enforcement of laws against resource plundering within these new (and existing) areas. Equally important, wildlife biologists stress, is electing politicians who are committed to biodiversity conservation, climate change mitigation, and protecting the safety, economic welfare, and livelihoods of indigenous people by preventing illegal land grabs and by rooting out criminal landowners.
- BioExplorer.net. (2024, July 29). Vieira’s Titi. Bio Explorer: https://www.bioexplorer.net/animals/mammals/monkeys/vieiras-titi
- Costa-Araújo, Rodrigo. “Critically Endangered Vieira’s titi monkey at risk in Brazil’s Arc of Deforestation.” Oryx. September 22, 2022:
https://www.oryxthejournal.org/blog/critically-endangered-vieiras-titi-monkey-at-risk-in-brazils-arc-of-deforestation - Costa-Araújo R, da Silva LG, de Melo FR, et al. “Primate conservation in the Arc of Deforestation: a case study of Vieira’s titi monkey Plecturocebus vieira.” Oryx. November 2022;56(6):837-845. doi:10.1017/S003060532100171X:
https://doi.org/10.1017/S003060532100171X - Dolotovskaya, S., Flores Amasifuen, C., Haas, C. E., Nummert, F., and Heymann, E. W.: “Active anti-predator behaviour of red titi monkeys (Plecturocebus cupreus),” Primate Biol., 6, 59–64, https://doi.org/10.5194/pb-6-59-2019, 2019:
https://pb.copernicus.org/articles/6/59/2019 - Lau AR, Clink DJ, Bales KL. “Individuality in the vocalizations of infant and adult coppery titi monkeys (Plecturocebus cupreus).” American Journal of Primatology. 2020 Jun;82(6):e23134. doi: 10.1002/ajp.23134. Epub 2020 Apr 16. PMID: 32298003; PMCID: PMC7881527:
https://pubmed.ncbi.nlm.nih.gov/32298003 - Ragen BJ, Mendoza SP, Mason WA, Bales KL. “Differences in titi monkey (Callicebus cupreus) social bonds affect arousal, affiliation, and response to reward.” American Journal of Primatology. 2012 Aug;74(8):758-69. doi: 10.1002/ajp.22026. Epub 2012 May 1. PMID: 22549396; PMCID: PMC4247787:
- Valeggia, C.R., Mendoza, S.P., Fernandez-Duque, E., Mason, W.A., Lasley, D.B. “Reproductive Biology of Female Titi Monkeys (Callicebus moloch) in Captivity.” American Journal of Primatology 47:183, 195 (1999):
https://www.sas.upenn.edu/~eduardof/Publications/Valeggiaetal,%20Reprod%20Biol%20Callicebus,%20AJP%201999.pdf - Wenzel, Fernanda. “The $20m flip: The story of the largest land grab in the Brazilian Amazon.” Amazon Illegal Deforestation News. Mongabay. February 14, 2023:
https://news.mongabay.com/2023/02/the-20m-flip-the-story-of-the-largest-land-grab-in-the-brazilian-amazon - https://www.iucnredlist.org/species/70330181/222944989
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4247787
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7041512
- https://frontiersinzoology.biomedcentral.com/articles/10.1186/s12983-016-0142-4
- https://www.conservationleadershipprogramme.org/news/new-monkey-species-discovered-amazon-rainforest/#:~:text=Scientists%20have%20discovered%20a%20new,monkeys%20found%20across%20South%20America.
- https://news.mongabay.com/2022/10/to-save-threatened-amazon-primates-in-brazil-turn-them-into-the-main-attraction
- https://nationalzoo.si.edu/animals/titi-monkey
- https://pubmed.ncbi.nlm.nih.gov/27155391
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6211037
- https://www.gbif.org/species/165729274
- https://kids.kiddle.co/Prince_Bernhard%27s_titi_monkey
- https://en.wikipedia.org/wiki/Prince_Bernhard%27s_titi_monkey
- Videos: A newborn Vieira’s titi monkey with father: https://vimeo.com/752597994 and Vieira’s titis in conversation (sound on!) https://www.youtube.com/watch?v=0QlPa7MBILw&t=50s
Written by Kathleen Downey, September 2024