Black and White Tassel-Ear Marmoset, Mico humeralifer
BLACK AND WHITE TASSEL-EAR MARMOSET
Mico humeralifer
Geographic Distribution and Habitat
Black-and-white tassel-eared marmosets occur in northern Brazil, in the dense forests of the Amazon in Para’ and Amazonas states, south of the Rio Amazonas, and along the western margin of the Rio Tapajo. They occupy the lower canopies of the forest, between 32 and 49 feet (10 and 15m) high.
Heavy rains cause waterlogged conditions in this region, resulting in plant and animal adaptions to cope with these conditions, such as living in trees. This terrain makes it difficult to conduct scientific studies involving equipment and electronics. So many species in this habitat, including the black-and-white tassel-eared marmoset, are understudied.
Black-and-white tassel-eared marmosets have adapted to the heavy logging activity in the Amazon forests. They are successful even in secondary-growth forests, which are dense with vines and fruiting plants, a preferred food choice for marmosets.
The black-and-white tassel-eared marmoset is also known as the Santarem or tassel-ear marmoset.
Formerly classified under the genus Callithrix, marmosets were separated in the early 2000s based on their distribution. Black-and-white tassel-eared marmosets are now grouped under Amazonian marmosets and classified in the “Mico” genus.
Their species name, “humeralifer,” comes from Latin, meaning “carrying a cape that covers the shoulders. ” This refers to their ear tufts, which meld into the bushy hair on their shoulders and back.
There have been reports of hybridization between the black-and-white tassel-eared marmoset and the Maués marmoset (Mico mauesi) in small overlapping pockets of their distribution, which may cause further taxonomic confusion in the future.
Size, Weight, and Lifespan
The black-and-white tassel-eared marmoset is one of the smallest primates in this region of Brazil, weighing between 10 and 11 ounces (280 and 310 g). The top of their head to the base of their tail measures 8 to 11 inches (20 to 17 cm). Their tails are much longer than their bodies, measuring 12 to 15 inches (31 to 37 cm).
They can live to be 15 years old in captivity. Wild lifespan is typically shorter.
Appearance
These small primates have long, thick, dark hairs all over their body, and their face is covered with skin. Their face is almost entirely pink except for around the eyes and nostrils. They have their namesake ear tufts in a long tassel-like shape that covers most of their ears. These tufts are black and white or grayish, and they blend into the gray cape-like fur on their shoulders (also called a mantle). This contrasts with the almost black fur around their face.
Their chest and back are lighter gray and almost white in places. Their fur darkens to black towards their hind legs and tail. The fur on their long tail is ringed and alternates between black and grey.
Males and females look similar (they are sexually monomorphic). Young black-and-white tassel-eared marmosets have a black stripe along the center of their head along their spine. Hair tufts on their ears become thicker and more noticeable as they become adults.
Like all marmosets, this species has curved modified claws instead of nails on their fingers and toes, except for their big toe, which has a nail, similar to other primates. The claws help them cling vertically to tree trunks and hold onto vines as they feed on sap.
Diet
They are omnivores, and like all marmoset species, black-and-white tassel-eared marmosets have claws and teeth built for gouging trees and feeding on gums (also called tree exudates). However, compared to other marmoset species, the black and white tassel-eared marmoset is less dependent on exudates as a primary food source and has adapted to have a varied diet of fruits and small prey, such as frogs and lizards.
They change their diet seasonally. During the drier months in the Amazon forest, only a few tree species bear fruit, and most of the moisture is trapped in the tree as gum or sap. Black-and-white tassel-eared marmosets stay close to these clumped food sources and feed on more exudates in the dry season. During the wetter months, they tend to travel further, looking for more food and feeding on more insects that they find opportunistically.
Late in the dry season and just before the rains, army ants swarm the forest floor in the thousands and hunt insects, spiders, and other arthropods. As these ants flush out insects, black-and-white tassel-eared marmosets follow the swarm and pick off arthropods that move up trees to escape.
Their diet of high-sugar exudates and high-protein insects supports their active lifestyle. They have to spend time looking for fruits that are clumped but spread about the forest or opportunistically hunting insects as they travel. Insects are less predictable and less clumped than fruit or gum sources. However, unlike plant food sources, insect numbers do not change seasonally.
Behavior and Lifestyle
They are social and arboreal (tree-dwelling) primates that spend most of their time traveling, feeding, and sleeping in trees. They come to the ground to cross roads that fragment the forest. Their locomotion combines quadrupedal walking, running, and trunk-to-trunk leaping, making them adaptable to different environments, even if deforestation has disturbed them.
Black-and-white tassel-eared marmosets can travel between 0.5 and 1.3 miles (0.8 to 2.1 km) daily, which may not seem a lot to us, but it is pretty far for these tiny primates. Marmosets eat more insects when they travel long distances and usually stay in one area when they find a good source of fruits or exudates. Their home range (where they do most activities) varies between 25 and 100 acres (10 to 40 ha). A marmoset family’s home range can overlap with other families, and groups tend to trespass into each other’s areas. Black-and-white tassel-eared marmosets are protective over their food resources, especially during fruiting season. Aggressive chirping and calls usually deter the trespassers when groups confront each other. These encounters rarely become violent, but they sometimes last up to 90 minutes!
At night, a family group huddles in dense vegetation or vines to protect themselves from predators and the elements. They have multiple sleeping sites and almost never use the same site on consecutive nights. Some biologists have recorded black-and-white tassel-eared marmosets sleeping in unusual sites, such as a tree hole, and clumped together on an exposed vine.
As small primates, marmosets carefully avoid predators like eagles and snakes. But if they spot a potential predator from a safe distance, they engage in mobbing behavior where multiple marmosets make alarm calls and look directly at the predator. Mobbing draws the attention of other animals who may join the mob and adds to the rising noise and attention towards the threat. This mobbing behavior deters predators from going into hunting mode because they have lost the element of surprise. In some mobbing episodes, birds can actively fly towards and peck or chase away the threat, making the area safe for the other animals as well.
Black and white tassel-eared marmosets have a heavy mantle of hair on their shoulders that looks like a cape.
They are omnivorous and feed less on tree gums than other marmoset species.
They live in a family with only one dominant male and female mating pair. Other members do not mate but help take care of the young.
They make a unique cricket-like chirp to communicate with each other.
They live in groups of 5-10 individuals, with the typical number being around six marmosets per family. The group comprises one mating pair and subordinate males and females that may be the offspring of the dominant male and female.
There is insufficient research on the activity patterns of the Mico genus, so we do not know how these species spend most of their time in the dense canopies of the Amazon forest. From other marmoset species, we can assume that black-and-white tassel-eared marmosets also spend most of their day searching for food. When a marmoset family finds a clump of food sources (such as a fruiting tree or a vine rich with gum), they will stay there and feed for most of the day. They spend their rest time grooming each other (allogrooming), napping, or playing with young ones. Before nightfall, family members will convene to find a suitably protected sleeping site among the vines or leaves.
Vocal communication is essential for marmosets, especially in dense forests where they cannot see each other. The most common marmoset vocalizations are trills, phee, twitters, and trillphee calls.
Trill calls do not carry far and are used to contact family members nearby. Phee calls are used for longer-range communication and are often associated with some form of identity, such as an individual, dominance hierarchy, or the caller’s sex. Phee calls are made between different marmoset families, especially during a confrontation. As the name suggests, “trillphee” combines a trill call that ends in a “phee” sound.
Research on the vocalizations of the common marmoset (Callithrix jacchus) shows that members develop and use unique sounds associated with individual identity, similar to how humans use names. This is a remarkable discovery because many researchers think it indicates a precursor to how humans developed language.
Black-and-white tassel-eared marmosets, in particular, make a specific “cricket-like” chirping noise used to contact other group members.
Marmosets also use olfactory senses (sense of smell) to communicate. They have glands on their chest, anus, and genitalia that they rub onto vines and trees. These scent marks can have information on identity, sex, and reproductive status. When a marmoset encounters one of these markings, it usually triggers more investigation and increased activity in the area. Marmosets also use their glands to mark areas with rich food sources, almost like putting a pin on a map. This way, the next time they come across the scent mark, they will know that a high-value food source is nearby and will search intensively to find and eat it.
More research is needed on the reproductive behaviors of wild black-and-white tassel-eared marmosets, but we can make some assumptions based on some observed behaviors and studies on other Mico species. Marmosets tend to have only one dominant male and female that mate and reproduce. Dominant females can be polyandrous (females who mate with multiple males), and males can be polygynous (mate with multiple females). The other (subordinate) males’ and females’ hormones are suppressed so they do not engage in mating behaviors. This prevents closely related members (for example, subordinate sons and dominant mothers) from mating.
Female and male black-and-white tassel-eared marmosets become sexually mature around 9 and 11 months. Estrus is when a dominant female’s reproductive hormones peak, particularly the estrogen hormone. When in estrus, the female’s reproductive organ (genitalia) swells, and she exhibits behaviors that indicate readiness for mating.
Their gestation period (when a female is pregnant) is between 4 and 5 months. They typically give birth to fraternal (non-identical) twins and have two sets of babies or litters yearly.
Baby black-and-white tassel-eared marmosets weigh 1.2-1.3 ounces (33-37 g), about 12% of their mother’s body weight. She has two of them that she needs to carry and feed. So it does take a village to raise the young, as other members help carry, groom, and care for the twin infants. The non-reproductive members of the family usually consist of older siblings of the newborns. So, the social cooperative rearing in marmosets benefits the overall survival of the family’s genetic line, and the young are not competing with their siblings.
Young marmosets instinctively cling onto the backs of their carers, and their fingers are so tight that they must be removed to be fed or carried by another family member. This is an excellent adaptation when you are a baby primate traveling several feet above the ground.
As young marmosets become more independent of their mother’s milk (around three months), they learn from their surrounding community of older marmosets. They pick up hunting techniques and learn to understand essential calls, especially those specific to the family, including sounds equivalent to names. Young marmosets reach adulthood in 9 to 10 months.
Black-and-white tassel-eared marmosets are a part of the complex, diverse ecology of the Amazon forest. They help control the abundant arthropod population in their range. Marmosets could be potential pollinators and seed dispersers as they travel and feed on fruits, but this role is largely unconfirmed. They are a food source for many species, including the black hawk-eagle (Spizaetus tyrannus).
Marmosets have a unique relationship with trees as exudate feeders. They gouge and technically create injury points on trees to create streams of gum they can feed on. Often, they will re-visit these injury points to feed on the same tree over many years. They prefer vines and older trees, which can withstand the injury and make more exudates. This ecological strategy allows marmosets to feed on gums without compromising or reducing food availability in the future. With age, trees lose their ability to regenerate, and the continued feeding injuries caused by marmosets can eventually kill them. Unless older trees die out and create light gaps in dense tropical jungles, new plant species cannot grow. Some researchers think that by targeting older trees, marmosets help forest tree species turn over and promote plant diversity.
Sometimes, marmoset feeding activity benefits other species of the Amazon. Other exudate-feeding species also use the gouged injuries that marmosets make to feed.
The International Union for Conservation of Nature lists the black-and-white tassel-eared marmoset as Near Threatened (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
The Amazon forest has been deforested for decades, resulting in irreversible changes to its ecology and structure. Deforestation removes trees and creates more roads, fragmenting forests into smaller patches of trees and causing related environmental pollution.
Logging activities in the forest have drastically affected all wildlife, especially tree-dwelling species like the black-and-white tassel-eared marmoset, which depends on trees for food and shelter. In patchy forest environments, marmosets are often forced to the ground to cross roads to reach food sources, which has resulted in them being victims of road accidents.
Black-and-white tassel-eared marmosets have been kept as pets locally, even if illegal.
The black-and-white tassel-eared marmoset 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.
National laws protect black-and-white tassel-eared marmosets in the Amazon National Park because development and human activity are restricted within their distribution.
Active conservation through the Tapajós-Abacaxis Corridor (by Conservation International Brazil and the Alcoa Foundation) includes local initiatives like the Urban Marmoset Project, which helps identify and map marmoset species found near human habitations. They help define on-the-ground conservation actions that can help reduce marmoset mortality through improved human-marmoset interactions.
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Written by Acima Cherian, September 2024