Geographic Distribution and Habitat
Black-handed tamarins (Sanguinus niger), also known as Western black-handed tamarins or black tamarins, are neotropical primates that live primarily in Pará, Brazil. Their home is bordered in three directions by rivers: the Amazon river in the north, the Tocantins river in the east, the Xingu river in the West. In the past, it was believed that the Gradaus river was the southern border of their territory, but more recent evidence has shown that they have expanded further south into the city of Confresa in the northeastern area of Mato Grosso, Brazil.
To have plenty of cover from predators and abundant trees for foraging, they prefer semi-deciduous primary forests. However, substantial deforestation has caused them to also have to make use of secondary forests that have been disturbed by human activity.
First thought to be a subspecies of red-handed tamarins (Sanguinus midas), black-handed tamarins were later recognized as their own species after primatologists studied differences between the teeth of the two species. The Tocantins river separates Western black-handed tamarins (Sanguinus niger) from Eastern black-handed tamarins (Sanguinus ursulus), which has prevented gene flow by keeping the two populations from reproducing.
Size, Weight, and Lifespan
Being very small primates, black-handed tamarins only weigh around 1 lb (500g). Their lifespan is not well documented yet, but members of the same genus generally have a lifespan between 10 and 18 years.
Black-handed tamarins are mostly covered in deep rich black fur with only a small area around their eyes and nose, as well as most of their ears, being hairless. Streaks of golden brown run all the way down their backs and stop at the top of their long tails. Their coat is fairly long and glossy. Their back legs are longer than their front legs, which allows them to leap between branches high up in the forest. Their fingers are long and slender which helps them quickly grab insects and fruit. They have claws on all of their fingers and toes with the exception of their big toes. Their thumbs are not opposable, unlike many other primates.
Around 80–90% of the blank-handed tamarin’s diet is fruit. Some of their favorite trees to forage from are Manilkara bidentata (also known as “cow-tree,” which produces a yellow berry), Pouteria lucuma (its fruit is called lucuma and some say it tastes like a sweet potato with a hint of maple), and Inga edulis (also known as “ice cream bean” and the smooth white filling in its pods tastes lightly of cinnamon). They also eat the gum from Parkia pendula trees. Occasionally, they eat insects as well (mostly orthopterans like grasshoppers and crickets).
Behavior and Lifestyle
Black-handed tamarins spend most of their day moving and foraging with smaller amounts of time in comparison spent eating, resting, and socializing. They follow regular routes between feeding patches and will frequently go back to the same areas during the day. When they eat insects, it occurs along their usual routes while foraging. They are arboreal and move through all levels of the forest spending most of their time in the canopy layers and very little time on the ground. Just like us, they are diurnal—they are awake during the day and sleep at night. They use all four legs to run along branches and jump from tree to tree.
To help protect themselves against predators, black-handed tamarins live and sleep in groups; this is crucial to their survival. They live in extended family groups of 4 to 16 individuals.
There is one dominant mating female whose chemical signals suppress ovulation in other females, if there is more than one in the group. Females have the choice to either stay in their natal family or join another family if they want to try to become the dominant female.
Young black-handed tamarins often spend time socializing through play that usually involves chasing. Sometimes, they hide behind branches and jump towards birds and butterflies attempting to capture or chase them. They also groom each other while resting in the middle of the day. Juveniles generally groom adults more than vice versa. While the adults are eating, infants are free to explore the tree crown on their own, but they are grabbed by one of the adults when the group is ready to keep moving.
As small animals with many predators, black-handed tamarins have to be vigilant and are always on the lookout. If a predator is spotted, they call to each other to alert the others in their group. They also use the areas around their sternum (breastbone) as well as above their pubic bones for scent marking. Two or three adults usually mark the same place one after the other. Infants beg for food from the adults by using loud and shrill vocalizations and they generally succeed in getting what they want.
In families of black-handed tamarins, only the dominant female breeds. However, when it comes to parenting, they have an all-hands-on-deck approach: every group member helps in raising the young. They also all help gather food and share with the infants. In their mating relationships, they can be monogamous, polygamous, polyandrous, or polygynandrous. Females begin ovulating between 12 and 17 months of age and males start producing sperm at 13 to 18 months. Infants are known to be born between January and mid-July, but it is not certain that these are the only times they can be born. Females are able to conceive again within 2 to 4 weeks of giving birth and infants are independent by 5 months old. They generally have fraternal twins like other Callitrichids, but can have 2 to 4 infants at a time. Triplets and quadruplets usually only occur in captivity.
Thanks to their high fruit diet, explored earlier, they defecate the seeds of those fruits all over the forest. This plays a key role in regenerating forests that are threatened by logging.
Black-handed tamarins are classified as Vulnerable by the International Union for Conservation of Nature (IUCN, 2020), appearing on the IUCN’s Red List of Threatened Species. There has been a 30% decrease in their population over the last 18 years. Deforestation in eastern Brazil has led to their forest habitats being disturbed and fragmented. As the forest cover that they rely on to protect themselves from predators continues to be decimated, they will likely become Endangered if preventative measures are not taken.
Predators of black-handed tamarins include humans, diurnal birds of prey, snakes, and some cat species such as margays and ocelots.
Some of the areas in which they live are protected like the Caxiuanã National Forest, Tapirapé-Aquiri National Forest and Carajás National Forest. However, the most southern area they live in are private properties where they aren’t guaranteed any protection. The species is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES).
Written by Elizabeth Joslin, July 2021