Black lion tamarin
The black lion tamarin (Leontopithecus chrysopygus) also known as the golden-rumped lion tamarin is a lion tamarin endemic to the Brazilian state of São Paulo, almost exclusively at the Morro do Diabo State Park. The lion tamarins are the most rare of the New World monkeys and for this reason, little is known about them. This black lion tamarin was thought to be extinct 65 years until rediscovery in 1970. This species is the most endangered of all the species within Leontopithecus. The IUCN has the black lion tamarin listed as endangered on their red list  because the total number of individuals is estimated to be around 1000. On the other hand there are experts who perceive this as a grave overestimate because recent studies have shown that the average range size for a black lion tamarin is closer to 106 ha rather than 66 ha that was previously estimated.. The average range size for a black lion tamarin has been estimated to be 64 to 127 ha. The black lion tamarin is usually found in groups ranging from 4-9 individuals. It lives in secondary and primary forests along the circumference of its home range. These forests are broken down into three distinct sections a scrub forest, a dry land forest, and a swamp. The average weight of the black lion tamarin is 590 - 640 g (ARKive).
The diet of the black lion tamarin is seasonal and varies with the different environments that the tamarin moves between. For example, when the tamarin is in the dryland forest, it usually eats a variety of fruits . while in a swampy environment they predominantly feed on the gum of different trees. In addition to seasonal variation the black lion tamarin seems to have daily and monthly cycles of food preferences as well. Independent of the environment they occupy, tamarins spend long periods each day in search for different types of insects and spiders to feed on. On average 80% of their time can be attributed to the search for insects, whether the black lion tamarin is physically digging or surveying for prey from above. Therefore their diet probably contains relatively high levels of protein. The search for insects and spiders can be broken down into two parts. The first part is physically looking for insects in areas that are on the forest ground that include leaf-litter, tree roots and decomposing trees. The places that the tamarins look for these insects are very intentional. They are consistently looking under dry palm leaves, loose bark, and tree cavities for extended periods. They use their hands that have specialized fingers for this type of prying. The second and main part of looking for insects is scanning from a tree. This is usually 4 meters above the forest floor. These black lion tamarins also eat the gum and fruit of trees. This has been recorded to be above the 10-meter mark. Because of the readily accessible fruits and gum, time spent looking for it was totaled to be 12.8% of their day compared to 41.2% of their day surveying high in the trees for insects and spiders.
Infant survival rate and care
During the spring, summer and fall months (August to March in Brasil), the black lion tamarins are mating and having their offspring.  Usually they have one litter per year, yet in 20% of the population of females, there can be two litters per year. While this is unusual, this has no baring on the mortality rate of the children of either litter. The mean litter size is roughly 2 infants for a female who has one litter that year. For a female that has two litters that year, she will usually have 3 or 4 offspring that year.In most mammals there is a usually 50:50 ratio of males to females. However, in the black lion tamarin species there is almost always a 60:40 male to female distribution within all the litters of a given population. Most of the deaths of infants within a population occur within the first two weeks after birth. The lowest survival rates of newborns were encountered in the care of a first time mother. Contrary to all conservation efforts, the number of animals that survive to adulthood in the wild is 10% higher than those that are in captivity. This means that the tamarins have a better chance surviving in the wild.
During the first few months after birth, the infant is unable to obtain food on its own. For this reason, the infant will latch onto the back of the parent and will ride them and will receive food from the parents. The first 4 to 5 weeks after birth they drink milk. After that the parents and other members of the group share food with the infants. Usually, until the age of approximately 15 weeks, the newly born infant will receive more food from others through sharing than through self-feeding. Because they feed on a large number of insects and spiders, the inexperienced tamarins rely on the older members of the group to share with them. Sharing is consists of both, offers from the parents and from successful begging attempts from the infant. Offers from the members of the group is highest around week 7 yet ceases at around 20 weeks after the infants' birth. After 15 weeks, there is a slow decline in sharing till about 26 weeks were food sharing was practically non-existent.
Calling structure and taxonomy
Within Leontopithecus, the black lion tamarin is the largest in size and has the lowest pitched calls. In addition to their lower pitch, the black lion tamarin also uses longer notes than the other species of the genus. The taxonomy of the black lion tamarin was debated because one group of taxonomists classify the lion tamarins by their geography into different species, while other taxonomists place them all into one species and then divide them into subspecies. Most recently they have agreed to focus classification predominantly on their geography. Sometimes characteristics such as long calls are analyzed to be used to classify different species, similar to birds that sing. These calls of the black lion tamarin can be used to defend a territory, maintain cohesion within the group, attracting a mate, and contacting individuals who might have lost physical proximity with the group. Most calls can be recorded in the morning, and can be attributed to the reuniting of mated pairs. These mated pairs are coupled up throughout the mating season. For the sake of differentiating within the genera, a black lion tamarin’s call is one whose syllables have the greatest range from start to finish yet start lowest.
Status and threats
As mentioned previously, the black lion tamarin is the most endangered of all the species within Leontopithecus. For this reason, there have been several attempts to bring the tamarins into captivity and to salvage what little home they have left within the Morro do Diabo State Park. The natural habitat of this animal has been exploited and destroyed through deforestation. This is the primary threat to the black lion tamarin. For this reason the IUCN have recorded that the number of individuals within the species is declining. Another threat is from people hunting them in some of the unprotected forests that the black lion tamarin inhabits. Some of these forests include the Fazenda Rio Claro and the Fazenda Tucano. In these parks there are roughly 3.66 and 1.0 individuals per square kilometer respectively. Hunting could cause the black lion tamarins to become entirely endemic to the Morro do Diabo State Park. Some black lion tamarins are being taken into captivity to breed to increase the number of individuals of black lion tamarins.
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