Geographic Distribution and Habitat
The saddleback tamarin (Leontocebus fuscicollis), also known as the Andean saddle-back tamarin (and previously referred to as the brown-mantled tamarin), is a species of New World monkey whose geographic distribution includes the South American countries of Bolivia, Brazil, Colombia, Ecuador, and Peru. These small primates make their homes east of the Andes Mountains (a nod to the primate’s alias) throughout the Amazon River Basin, dwelling in lowland and lower montane rainforests, seasonally flooded forests, remnant forests, and secondary forests. Riverbank primary forests with thick understory provide alternative habitat. The monkeys reside at widely ranging altitudes, from 328 to 3,937 ft (100–1,200 m) above sea level, but they are more commonly found in the middle and lower levels.
The International Union for Conservation of Nature (IUCN) revealed in its July 2020 updates of the IUCN’s Red List of Threatened Species that evolutionary analyses of the Saguinus genus, conducted in 2016, resulted in moving the saddleback and black-mantled tamarins into their own genus, Leontocebus. Biogeography, morphology, behavior, ecology, and phylogeny were considered. In 2015, the IUCN had already updated the saddleback tamarin’s species name from leucogenys to fuscicollis. Today the full taxonomic name for this primate is Leontocebus fuscicollis. It is ranked as Least Concern on the IUCN’s Red List of Threatened Species. (The updated taxonomic name for the black-mantled tamarin is Leontocebus nigricollis; it is also ranked Least Concern.)
With an updated name comes parenthood. The saddleback tamarin is the “parent” species to four “children” (subspecies), two who take a hyphenated name and two who do not:
- Ávila Pires’s saddle-back tamarin (Leontocebus. fuscicollis avilapiresi); like its parent species, the IUCN has ranked this subspecies as Least Concern.
- Spix’s saddle-back tamarin (Leontocebus f. fuscicollis), ranked Least Concern.
- Lako’s saddleback tamarin (Leontocebus. f. primitivus), ranked Data Deficient.
- Mura’s saddleback tamarin (aka, gray-fronted tamarin) (Leontocebus. f. mura), discovered in 2009 in a remote region of the Amazon in the country of Brazil and not yet fully assessed by the IUCN; therefore, this species has no ranking.
Ávila Pires’s, Lako’s, and Mura’s saddle-back/saddleback tamarins are all found in the central western region of the Brazilian state of Amazonas, south of the Rio Solimões, west of the Rio Madeira.
Spix’s saddle-back tamarins are found in several locations: east of the Jutaí River within the Brazilian state of Amazonas; in the upper Juruá River Basin within the Brazilian state of Acre; and between the Tapiche, Blanco, and Yavari rivers in the country of Peru.
Size, Weight, and Lifespan
About the size of a squirrel, the saddleback tamarin has a head-to-body length of 8.1–9.1 in (21–23 cm). Its tail adds another 17 in (43 cm). Body weight is from 12.3 oz to barely over 1 lb (350–456.5 g). Sexual dimorphism is not pronounced in the species; females and males look very much alike.
Lifespan for wild saddleback tamarins is between 8 and 13 years. Those held in captivity have a maximum lifespan reported at 24.9 years.
What Does It Mean?
The history of the evolution of a species or group, especially in reference to lines of descent and relationships among broad groups of organisms.
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Thick, dark fur drapes the shoulders, arms, and upper torso of this small New World monkey. On its back, Mother Nature (or perhaps Her hairdresser) has painted a patch of fur, intermingling orange-yellow strands with black blotches of hair, creating a speckled pattern known as “agouti” (giving the primate its “saddle”). Orange-yellow fur covers the monkey’s hindquarters, and black fur clings to its long tail, fanning out toward the tip. Long, narrow hands, thought to be an adaptation, help the saddleback tamarin reach into small crevices and capture insects.
Scalloped ears jut out from a small, round head capped with black fur. The muzzle is flat and, in some individuals, powdered with white hairs, or whiskers. These white accents might also decorate the monkey’s brow. Copper-colored eyes survey the world and suggest a pensive (or maybe judgmental?) mien.
Among the four subspecies, coat coloring varies from bright orange, black, or white. Some individuals are cloaked in fur coats that appear to be a solid dark color. Furry faces also vary in color and the skin may be light or dark, with some individuals having conspicuous whiskers and others without.
Saddleback tamarins are in the same family, Callitrichidae, as marmosets. So it’s not surprising that these two species share certain physical traits. Both have long, non-prehensile tails; they have two, rather than three, molar teeth on either side of their jaw; and—unlike most monkeys of the neotropics region—both are fitted with claws, rather than nails, on all their phalanges, except for their big toe, which has a nail. Their thumb is non-opposable. Both species are petite, with marmosets the tinier of the two. But the main physiological difference is that marmosets are fitted with jaws and teeth adapted to biting into the barks of trees, thereby creating small holes where sap or other plant exudates collect. Not to worry. What saddleback tamarins lack in dentition, they make up with an adapted cunning.
These diminutive omnivores eat a smorgasbord of foods, including fruits, flowers, nectar, eggs, snails, lizards, frogs, spiders, and insects. When readily available, they enjoy plant exudates (gums, saps, and latex) as well and will exploit an opportunity to dine on this sticky sustenance. Because their teeth are inferior when it comes to gouging holes in trees—necessary to stimulate the flow of plant exudates—these cunning tamarins wait for another primate to do the work. Opportunist or thief? The pygmy marmoset, a sympatric species, is a gum-eating specialist—hence, his title “gummivore.” Once this smaller monkey has gauged a hole in a tree and sap is flowing, the saddleback tamarin muscles in and claims the sweet dining spot as his own.
Saddleback tamarins are diurnal and arboreal, meaning that they are most active during daylight hours and spend most of their time in the trees, respectively. They wake at sunrise and spend almost the entire day foraging, as a group, swinging or leaping acrobatically from branch to branch in search of food. Daily travel is about 1.12 mi (1.8 km). They move through the lower layers and forest understory, up to 32 ft (10 m) above the ground. Should they descend to the ground, they walk or run quadrupedally (on all four limbs). Their strong claws help them to clamber back up into the relative safety of the trees. Because of their small size, they are vulnerable to predators, particularly birds of prey (such as the harpy eagle), snakes, and ocelots.
Unlike their close cousin, the larger moustached tamarin (Saguinus mystax), who travels in the middle canopy of the forest, above 32 ft (10 m), and selects sleeping sites higher up in the trees—and never uses the same site for more than two consecutive nights—saddleback tamarins choose sleeping sites at lower levels and reuse the same site for up to four consecutive nights. Ideally, they select an area where they have exclusive foraging rights, typically amidst multiple fruiting trees, so they can maximize their daily foraging expeditions. To mitigate predator risk, safety is an important and overarching factor when choosing sleeping sites. Retiring before dusk, the monkeys find security in the profusion of tangled vines and trees. Saddleback tamarins are also known to sleep overnight inside tree hollows or at the fork of large tree trunks.
Saddleback tamarins are considered to be “phyletic dwarfs,” meaning that their small size is related to their evolutionary development.
Like all members of the Callitrichidae family—with the exception of Goeldi’s marmoset—saddleback tamarins give birth to dizygotic twins (two eggs are fertilized by two separate sperm), more commonly known as “fraternal” or “non-identical” twins.
They may not be identical twins, but tamarins have been called “cellular mosaics,” thanks to a genetic phenomenon known as “hematopoietic chimerism.” During gestation, stem cells are exchanged between the respective placentas of dizygotic twins. Hematopoietic tissues, commonly found in bone marrow, display stem cells of both self and sibling DNA of tamarin twins.
Social animals, saddleback tamarins live in family groups ranging from 4 to 15 individuals. Groups of just two have been observed, with eight individuals being the average group size. Typically, a group (or “troop”) comprises a dominant breeding female, one or several adult males, and young offspring.
Size of home range depends on availability of food sources and varies with the seasons, fluctuating from 39.5 to 297 acres (16–120 ha). Home ranges often overlap with that of other tamarin troops, so interactions are common. Saddleback tamarins are known to defend their turf from outsiders; chasing and fighting may occur. But not all intergroup encounters are aggressive—some are peaceful. Monkeys from different troops often feed, unbothered, by their neighbors’ presence. Some of these interactions with neighboring tamarins include grooming and playing, and, sometimes, copulation occurs with the outsiders. Amiable intergroup encounters serve specific functions, according to wildlife biologists. Foremost, larger numbers provide a resource defense; they also provide the opportunity for non-sexually mature individuals and non-breeding adults to get to know potential mates from neighboring troops. For individuals who engage in sex with members from outside troops, migration from one troop to another is known to occur.
Sympatric primate species include pygmy marmosets (genus Cebuella), Goeldi’s marmosets (Callimico goeldii), and moustached tamarins—with occasional interactions with red-chested mustached tamarins (Saguinus labiatus). Wildlife biologists believe that mixed-species associations may be a strategy of predator protection (with “safety in numbers”).
Saddleback tamarins are not the most loquacious primates, but they rely on their small pocket of vocalizations to send specific messages. To convey predator danger, they sound alarm calls; to determine one another’s whereabouts when foraging, they sound contact calls. Bird-like trills, chirps, and whistles are the most common vocalizations associated with saddleback tamarins.
Olfactory communication is an important part of daily life for saddleback tamarins. Mother Nature has given these monkeys a well-developed olfactory system and fitted their small bodies with specialized scent glands in the sternal, anogenital, suprapubic regions. The monkeys regularly scent mark to convey specific information, leaving their secretions on substrates, and sometimes, on each other: a behavior known as “allomarking.” Allomarking may be associated with environmental changes or aggressive encounters. During aggressive encounters, saddleback tamarins are known to scratch their chest and suprapubic area, stimulating secretions from the sternal and suprapubic gland and soaking the animal’s fur.
Scent marking serves three key functions: demarcates territorial boundaries, denotes social status and reproductive dominance, and signals mate attraction. Individuals may include drops of urine in these secretions.
To demarcate territorial boundaries, the monkeys scent mark feeding trees found in overlapping ranges of neighboring troops.
- Reproductive status/dominance
Females scent mark to convey their reproductive status, often combining vaginal fluids in their secretion. A male may “overmark” a female’s scent; that is, he may deposit his own scent mark over her secretions in a strategy to claim, or guard, the female as his copulation partner.
- Mate attraction
Scent marking may be used as an advertisement for a mating partner, either within an individual’s troop or from a neighboring saddleback tamarin troop. Wildlife biologists hypothesize that because most members of a troop are closely related, some members may look to neighboring troops for reproductive vacancies and copulation partners.
Like most tamarin species (and marmosets), saddleback tamarins usually abide by a polyandrous society: the most dominant female of a troop mates with several male members. Subdominant females are reproductively suppressed, thereby ensuring the dominant female’s reproductive success.
Female saddleback tamarins reach sexual maturity at about 18 months of age. Males lag behind a bit, reaching sexual maturity at about 2 years of age.
The gestation period for the species is about 150 days, and twin births are the norm—greater than 80 percent of all births (same with marmosets). Saddleback tamarins weigh a mere 1.4 oz (39.9 mg) when they are born. Most births occur during the wet season, from September to March, when food sources are plentiful. Although babies begin eating solid foods at about one month old, they are not considered fully weaned from their mothers until 3 or 4 months of age. By age two, they are considered to be independent.
New mothers need all the help they can get in caring for two infants simultaneously. Luckily, alloparenting is also the norm with this species, with all members of a troop, especially the males, stepping in to help with childcare. Males, more often than the infants’ mother, carry the babies on their back as they travel through the trees for the first three months of the infants’ lives. Energetically spent from nursing two infants and unable to safely carry both her babies at once, a mother relies on this assistance. Older half-siblings also help out with infant care. From a scientific/biologic viewpoint, alloparenting helps ensure the species’ survival.
Monogamous societies, in which mating is for life, have been reported in the species, as have the rare polygynous society, in which one male mates with multiple females. Overall, however, saddleback tamaris are cooperatively polyandrous, with females mating with multiple males.
The species’ taste for, and consumption of, an overwhelming quantity of insects helps to regulate the forest’s insect population. And their dietary penchant for fruits makes these small monkeys natural seed dispersers. Seeds that pass through their digestive tracts are excreted in their poop and thereby help to regenerate the tamarins’ forest habitat.
Due to the species’ widespread geographic distribution and no immediate threats to its survival, the saddleback tamarin is classified as Least Concern by the International Union for Conservation of Nature (IUCN, April 2020), appearing on the IUCN Red List of Threatened Species.
These monkeys are routinely killed, however. Locals hunt them for their flesh, known as “bushmeat.” (Although, being such small monkeys, they are less of a meal than more heavily hunted larger monkeys.) Babies are kidnapped (after killing the mothers) and sold into the illicit wildlife pet trade. But because these activities have not (yet) resulted in a significant population decline, the species’s overall population is considered stable. And while habitat loss may not be a paramount, immediate threat against this species—only because of the monkeys’ large population numbers—deforestation throughout their Amazon Basin home is a dire reality.
Furthermore, the deliberate destruction of pristine forest habitat for agricultural, logging, and mining purposes has been linked to devastating fires throughout the Amazon rainforest. Besides the negative impact on biodiversity in the region, these fires exacerbate the climate crisis by increasing the release of greenhouse gases.
According to the conservation group Monitoring of the Andean Amazon Project, the countries with the highest primary forest loss in 2020 were: 1) Brazil, 2) Bolivia, 3) Peru, 4) Colombia, 5) Venezuela, and 6) Ecuador—home countries of saddleback tamarins.
It gets worse. Local socio-environmental/climate crisis activists—those individuals protesting, rallying, and raising their voices to save their countries’ rainforests—face grave danger. According to the human rights watchdog group Global Witness, in 2019 (the most recent year reported), more than 212 people were killed worldwide while defending the environment. This somber number includes 64 environmental activists in Colombia and 24 in Brazil. The dead were environmental activists, members of indigenous tribes, and farmers trying to defend their livelihood from exploitation.
And it gets even worse. A cultural of impunity pervades the Amazon rainforest region, particularly in Brazil, where intimidation and murder of activists remains a dire threat. Nearly 90 percent of these murderers have never been brought to justice. Rather, it’s the activists who have been portrayed as criminals or “environmental terrorists.” Collusion between an indifferent government and a corrupt police force allow these environmentalist killings to continue.
The saddleback tamarin 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.
Those saddleback tamarins living within the boundaries of wildlife reserves, such as the Tambopata National Reserve in Peru, are afforded a level of protection.
Conservationists call for further studies of this species, particularly its life history, ecology, and population trends. But conservation efforts must also consider human preservation. Pointedly, locals who hunt these small monkeys do so for reasons of subsistence. Likewise, locals who capture the monkeys for the wildlife trade do so to put a bit of much-needed cash in their pockets. Alternative resources that improve quality of life for indigenous people along with the creation of educational programs are critical in protecting this (and all) species. Successful conservation is about survival . . . for both human and nonhuman primates.
And most certainly, protections for those who advocate on behalf of the environment must be created, strengthened, and enforced.
In addition to Monitoring of the Andean Amazon Project and Global Witness, other conservation groups working to raise awareness, and thereby saving tamarin habitat, include The Nature Conservancy, Saving Nature, and Rainforest Trust.
Written by Kathleen Downey, April 2021