The white-eared titi monkey (Plecturocebus donacophilus) also known as the Bolivian titi or Bolivian gray titi, is a species of titi monkey, a type of New World monkey, from eastern Bolivia and an area of western Brazil. The species has a range that extends east from the Manique River in Beni Department, Bolivia to southern Rondônia in Brazil. The southern end of its range includes forests around the city of Santa Cruz de la Sierra. It is a medium-sized monkey with a grey back, orange underside and distinctive white ear tufts. It has an omnivorous diet, eating fruits, other plant materials and invertebrates. It is a monogamous species and lives in small groups of two to seven members consisting of the pair and their offspring. The family group has a home range of 0.5 to 14 hectares (1.2 to 34.6 acres) and the adults have a complex vocal repertoire to maintain their territory. It is also known for its characteristic twining of tails when groups are sitting together. White-eared titis can live for more than 25 years in captivity. The white-eared titi population has a declining trend. The decline is believed to be mainly caused by human-induced habitat loss and degradation. Despite this, the International Union for Conservation of Nature (IUCN) classified the species as being of least concern in 2008 as it has shown adaptability to habitat disturbance and is found over a wide range.
Taxonomy The white-eared titi belongs to the New World monkey family Pitheciidae, which contains the titis, saki monkeys (Pithecia), bearded sakis (Chiropotes), and uakaris (Cacajao). It is a member of the subfamily Callicebinae. It was first described as Callicebus donacophilus in 1836, but was reassessed based on molecular evidence and recombined as a species within the genus Plecturocebus. Within the new genus Plecturocebus, the white-eared titi is part of the P. donacophilus group with the Rio Beni titi (P. modestus), Rio Mayo titi (P. oenanthe), Olalla brothers' titi (P. olallae), white-coated titi (P. pallescens), and Urubamba brown titi, (P. urubambensis). The white-coated titi has sometimes been considered a subspecies of the white-eared titi, but they are treated as separate species in the latest edition of Mammal Species of the World.
Physical description The white-eared titi is a medium-sized primate with grey to orange pelage. The species does not exhibit sexual dimorphism; the male's head and body length averages 311 millimetres (12.2 in) while females average 340 millimetres (13 in). The white-eared titi's fluffy tail is longer than the length of its head and body together. It typically has thick fur, with a dorsal side and limbs that vary in colour from grey agouti to orange agouti, with an orange underside and white ear tufts. Body weight ranges from around 800 to 1,200 grams (1.8 to 2.6 lb), with the female generally a little lighter. It has the dental formula 2.1.3.32.1.3.3 × 2 = 36, meaning that on each side of the jaw it has two incisors, one canine tooth, three premolars, and three molar teeth. The canine teeth are relatively short when compared with other New World monkeys. In captivity, the white-eared titi has been known to live for over 25 years.
Behaviour The white-eared titi is cryptic, diurnal and known to live in small family groups. It is a monogamous species that is thought to mate for life and lives in groups that usually consist of two to seven members; an adult pair and up to five young. Multi-male groups have also been recorded. Offspring are carried by the male, and are always with them, except when feeding. Between the ages of two and four years, offspring will disperse from the natal group, with females leaving earlier than the males.
There is a strong bond between the adult mating pair, they stay close and carry out activities together. Either member of the pair may follow the other and leadership changes through the day. Evidence of the strength of the pair bond is shown by grooming, huddling together with their tails twined, nuzzling, and gentle grasping. Titi monkeys are highly territorial and when confronted with another family group, both will respond with threatening behaviour, males showing increased agitation towards intruding males. When not close together, the pair show a significant amount of distress and agitation. Titi monkeys are well known for their vocal communication, and have a complex repertoire of calls. The calls can be divided into two categories: high-pitched quiet calls and low-pitched loud calls. Vocalisations are often combined and repeated to form sequences that are used to indicate distress, conflict, play, bonding, disturbance, and to strengthen territory. The high-pitched quiet calls are mostly used when the monkeys are disturbed, but may also be used before or after group calling, while foraging, or to find other members of the group. The loud low-pitched calls are mostly used in long distance group calling. Their function is to ensure adequate spacing between the home ranges of different family groups. These vocalisations are known as duets, and generally involve the male and female. If a neighbouring group is within earshot of these calls they will respond with their own duetting.
The white-eared titi is arboreal, spending most of its time in the lower strata of the forest. It may enter the main canopy when travelling longer distances and may also cross small areas of open ground, though the latter is rare. During normal movement through its environment it is quadrupedal and mostly walks, clambers and leaps, but it can also bound and climb. It leaps small distances, no more than a few body lengths, between trees where vegetation is not thick enough to support its primary forms of locomotion. When travelling on the ground it is said to use a "bounding movement" whereby it leaps more than 1 metre (3.3 ft) off the ground. The titi monkey prefers branches which are less than 5 centimetres (2.0 in) in diameter and its tail never touches the support it is on.
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