Brown Titi, Plecturocebus brunneus
BROWN TITI
Plecturocebus brunneus
Geographic Distribution and Habitat
The brown titi (Plecturocebus brunneus) is endemic to the Brazilian state of Rondônia. It is found nowhere else in the world. Their range is bounded by the Mamoré, Madeira, and Jiparaná rivers. They make their homes in the well-drained, nutrient-rich rainforests of the Amazon. They are relatively tolerant of habitat disturbance, but their population has been decreasing due to unsustainable levels of deforestation.
Titi monkeys are considered “monophyletic”—that is, they all share a common ancestor that is not shared by any other group. Titi monkeys are classified into three genera: Cheracebus, Plecturocebus, and Callicebus. Brown titis were formerly classified into the genus Callicebus but were reevaluated in 2016 and placed into Plecturocebus. The closest relative of the brown titi is believed to be the coppery titi, P. cupreus.
Size, Weight, and Lifespan
Both males and females weigh about 2.2 pounds (1 kg) at full size. Their head and body length is about 11 to 15 inches (29 to 39 cm). They are believed to live to about 25 years of age.
Appearance
Brown titis are covered in a thick coat of hair. Their backs, shoulders, and legs have an agouti coloration—a type of coloration in which each hair has multiple bands of color. From a distance, the agouti coloring appears brown and blends in seamlessly to the surrounding tree bark. Their arms, necks, and bellies are rusty red. They have a “cap” of black on the tops of their heads and ears. They tend to have a hunchbacked appearance at rest, with their head remaining rather low and their spines curved behind them. This scrunched-up posture accentuates the length of their tail, which is usually dangling underneath them. Their tails are not prehensile, meaning they are not capable of tightly grasping like some primates’. Males and females are nearly identical to each other, including being about the same size at full growth. Young brown titis are born with their adult coloration, looking like miniature versions of their parents.
Diet
Brown titis are usually characterized as frugivores—fruit eaters—though they have a varied diet composed of leaves, seeds, and small invertebrates in addition to fruit. Their diet likely varies somewhat with the seasons, as titis are known to consume more leaves and less fruit during the dry season. Pregnant titis tend to eat more insects, likely to increase their protein intake
Behavior and Lifestyle
Brown titis are fully arboreal, living their entire lives in the trees and coming to the forest floor only rarely. They move about quadrupedally—on all fours—usually by walking, climbing, and leaping. When they find themselves on the forest floor, they move swiftly in a quick bounding gate, sometimes leaping up to three feet (1 m) off the ground. Brown titis are diurnal—awake during the day and asleep at night. They often start their day with a hearty breakfast—that is, a feeding session of several hours early in the morning. They take a midday siesta to recoup some energy, then continue to forage throughout the afternoon. They travel between 0.3 to 0.9 miles (0.5 to 1.5 km) each day in search of food. At dusk, they retreat to a secluded vine thicket high in the canopy to spend the night with their family group. They usually return to the same sleeping spot night after night. In the cold months, brown titis sleep in to conserve energy, as fruit is harder to find during this time of year.
Mated pairs of brown titis are attached at the hip—or in this case, the tail. Tail twining, in which two titis wrap their tails around each other as they rest, is commonly seen between mated pairs and even occurs in sleep.
Brown titis have been seen chewing leaves from legume and pepper plants and rubbing the pulp on their chest. It is not known with certainty why they do this, but it has been hypothesized that it is a form of self-medication to repel parasites. The plants they use to rub on themselves are also often the same ones that are used in traditional medicine by local people.
Brown titi groups are usually small and formed by a mating couple and their offspring. Their group may include up to three generations of offspring at one time, for a maximum of five individuals in a typical group. Their home range size varies from 0.2 to 12 square miles (1.5 to 30 square km). There have been no recorded instances of male or female dominance. Rather, brown titis tend to be egalitarian in how their family groups are led. There is rarely any aggression within family groups, but there may be confrontations when two separate family groups encounter each other. Overall, titis are not known to be particularly aggressive.
Olfactory communication is highly important for titis, and brown titis are no exception. Titis have scent glands located on their chests, which they rub on branches and tree trunks to communicate information through smell. Males smell their partner’s genitals before copulation, possibly to learn information about her estrus cycle. Visual communication includes body posturing and facial expressions, such as body swaying, avoiding eye contact, shaking the head, or raising the tail to indicate anger. Brown titi vocalizations are varied and include whistles, grunts, screams, moans, and panting. Mated pairs are known for their sunrise duets, in which the male and female loudly vocalize at the outer edge of their range. Other pairs in the vicinity join in the cacophony. Touch is another important method of communication for titis. Grooming is an important form of bonding, and a study of the closely related coppery titi found that grooming makes up nearly a third of all social contact. They make physical contact with a groupmate nearly half the time.
Among the few monogamous primates, titis are generally loyal to a single partner for many years, if not for life. After mating, females tend to give birth between November and March, birthing one baby at a time. Their estrus cycle lasts between 17 to 21 days. Fathers play the main parenting role, performing nearly all childcare duties, and handing the baby to its mother only for nursing. At all other times, until the baby is more independent at about four months old, it is latched onto its father’s back. Young stay with their family group until they are about two or three years old. When they reach this age, they may be encouraged to leave the group, especially after the birth of a new sibling.
The most significant predators of brown titis are birds of prey, such as eagles and hawks. Arboreal snakes may also serve as a predator to brown titis. Brown titis primarily avoid predators by hiding and using their dull coloration to blend into tree branches and trunks. Brown titis are sympatric with other primate species—that is, they live in the same environments as other species. They are mostly avoidant of other primate species, but in one documented case, a female brown titi was attacked and killed by tufted capuchins (Sapajus apella) when feeding from the same tree. It has been reported, but not confirmed, that brown titis may overlap slightly in territory with the red-bellied titi (P. moloch). It has been speculated that there may be some hybridization between the two species, but more research is needed to confirm this.
The International Union for Conservation of Nature lists the brown titi as Vulnerable (IUCN, 2015) appearing on the IUCN’s Red List of Threatened Species. This assessment is based on the ongoing population loss experienced by the species, believed to be more than 30% over the past three generations or about 27 years. Because of ongoing deforestation, this population loss is not expected to stop or slow without significant and immediate conservation action.
The Brazilian state of Rondônia has been subject to an alarming rate of deforestation—22% of its forests have been lost between 2000 and 2018. This deforestation is a result of increased human settlement in Rondônia, as forests are removed to make room for human settlements, agriculture, energy infrastructure, and roads. About half of the historic habitat of brown titis has been impacted by human settlement. One study found that the high rate of deforestation in Rondônia will actually have impacts on the regional climate. Models show that extensive deforestation may actually increase rainfall in agricultural and urban areas while leading to warmer and drier conditions in protected forests. These conditions will have an untold number of ecological consequences, putting stress on a species that is already in decline.
Global climate change is another looming threat to brown titis. The state of Rondônia continues to see ever-increasing mean annual temperatures. Between 1979 and 2023, the average mean annual temperature in the state increased by 2.3 degrees Fahrenheit (1.3 degrees Celcius). Climate change is more than just warmer temperatures, however. It also results in changing precipitation rates, more frequent and intense storms, flooding, droughts, changes to vegetation cycles, and much more. Climate change will impact not only the humans living in Rondônia but also the vast array of animal and plant species that make the region home, including brown titis.
Brown titis are 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. Parts of their habitat are projected, such as in the Jamari National Forest, Rio Ouro Preto Extractive Reserve, Jaru Biological Reserve, and the Samuel Ecological Station.
- Carneiro, J., et al. 2018. Phylogeny, molecular dating and zoogeographic history of the titi monkeys (Callicebus, Pitheciidae) of eastern Brazil. Molecular Phylogenetics and Evolution 124:10-15.
- De Sales, F., Santiago, T., Biggs, T. W., Mullan, K., Sills, E. O., & Monteverde, C. 2020. Impacts of protected area deforestation on dry-season regional climate in the Brazilian Amazon. Journal of Geophysical Research: Atmospheres 125.
- Oliveira, B., Souza-Alves, J., Oliveira, M. 2020. Potential self-medication by brown titi monkeys, Plecturocebus brunneus, in an urban fragment forest in the Brazilian Amazon. Primate Biology 7:35-39.
- Witczak, L., Blozis, S., Bales, K. 2022. Assessing variability in affiliative maintenance behaviours in captive coppery titi monkeys, Plecturocebus cupreus. Animal Behavior 191:117-124.
- https://www.iucnredlist.org/species/41558/17974148
- https://animaldiversity.org/accounts/Callicebus_cupreus/
- https://nationalzoo.si.edu/animals/titi-monkey
- https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-dusty-titi-monkey/
- https://www.meteoblue.com/en/climate-change/rond%C3%B4nia_brazil_3924826
Written by K. Clare Quinlan, April 2024