Bolivian Gray Titi Monkey

About the Bolivian gray titi monkey

The Bolivian gray titi monkey is also known as the white-eared titi, and both names describe the same New World monkey, Plecturocebus donacophilus. It was first described in 1836 as Callicebus donacophilus, but molecular evidence later moved it into the genus Plecturocebus along with several close relatives, including the Rio Beni titi, the Rio Mayo titi, and the white-coated titi, which was once treated as one of its subspecies. It belongs to the family Pitheciidae, the group that also contains saki monkeys, bearded sakis, and uakaris, and sits within the subfamily Callicebinae alongside the other titis.

Physically, it is a medium-sized primate with grey to orange fur. The back and limbs run from grey agouti to orange agouti, the underside is orange, and white tufts mark the ears. Its tail, thickly furred, is longer than its head and body combined. There is no real size difference between the sexes: males average 311 millimeters (12.2 in) in head-and-body length and females average 340 millimeters (13 in), with females running slightly lighter in weight. Adults weigh between 800 and 1,200 grams (1.8 to 2.6 lb). Its jaw carries 36 teeth in total, with canines that are notably short compared to other New World monkeys.

In the wild, the species occupies a defined stretch of South America. Its range runs east from the Manique River in Bolivia's Beni Department into southern Rondônia in Brazil, and its southern edge includes the forests around the city of Santa Cruz de la Sierra. Within Bolivia it is found across the upper Mamoré, Grande, and San Miguel river basins.

Behavior and diet

The Bolivian gray titi monkey is monogamous and appears to mate for life, living in small family groups of two to seven that pair an adult male and female with their offspring, though multi-male groups have been recorded too. The bond between the mated pair is close: the two stay near each other, groom, huddle with their tails twined together, and take turns leading the group through the day. When separated, both animals show visible distress. Offspring are carried by the male except while feeding, and they disperse from the family group between two and four years old, with females typically leaving first.

Titis communicate through an elaborate set of calls split into two kinds: quiet, high-pitched sounds used when disturbed or while foraging, and loud, low-pitched calls used for long-distance contact between groups. The loud calls are often sung as duets between the male and female, and they serve to keep neighboring family groups spaced apart; a nearby group that hears one will typically call back.

Diet is omnivorous, dominated by leaves, especially young, protein-rich leaf buds, which the animal spends long stretches resting to digest. Titis of this kind eat more than 100 species of plants and fruit, and also take small insects such as ants, moths, and butterflies, along with spiders and any flying prey that comes within reach. Leaf-eating rises during the dry season, while insect consumption is thought to increase during lactation to boost dietary protein.

The species is diurnal and arboreal, active for around 11.5 hours a day with about 2.7 hours of that spent feeding, mostly in two main bouts, morning and afternoon. It rests through the middle of the day and sleeps on branches at least 15 meters (49 ft) up, again huddled with tails twined. Moving through the forest, it walks and clambers on all fours in the lower and middle levels, entering the main canopy only for longer trips and rarely crossing open ground; when it does travel on the ground, it moves in bounding leaps of more than a meter (3.3 ft).

Range and habitat

The Bolivian gray titi monkey is native to eastern Bolivia and an adjoining slice of western Brazil. Its range extends from the Manique River in Bolivia's Beni Department east into southern Rondônia, and the southern limit of that range takes in the forests surrounding Santa Cruz de la Sierra. Within Bolivia, it occupies the upper Mamoré, Grande, and San Miguel river basins.

It favors tropical humid forest, though it leans toward drier stretches of that habitat rather than the wettest ones, and it is closely tied to riparian zones and gallery forest along waterways. It also turns up at the edges of open habitats such as grasslands and swampy grasslands, generally choosing the densest, thickest sections of vegetation available. The species has shown real tolerance for habitat disturbance, a trait that has helped it persist even near expanding cities.

Conservation status

The Bolivian gray titi monkey is classified as Least Concern (LC) by the IUCN, a status set in 2008. Its population is declining, driven mainly by human-caused habitat loss and degradation, but the decline has not been fast enough, and the animal's range wide enough, to place it in a threatened category. It is also listed on CITES Appendix II.

The main pressure on the species is deforestation for agriculture, concentrated most heavily around Santa Cruz de la Sierra, though the monkey still survives inside the city limits and along the margins of rural land. It has few natural predators and has proven adaptable to disturbed habitat; farmland that isolates pockets of forest can even work in its favor, since farmers sometimes keep hunters off their land. The species is also able to cross open ground between forest fragments. Even so, that fragmentation can limit its ability to establish new territories and reduce breeding opportunities, and forest corridors linking fragmented patches have been proposed as a way to support the population. Some protection already exists within the Beni Biological Station Biosphere Reserve and Amboró National Park in Bolivia. Recorded predators include crested eagles, ornate hawk eagles, jaguars, arboreal snakes, and, for infants, tufted capuchins.