Leontopithecus chrysopygus

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. Its limited geographical range makes it the rarest of the New World monkeys, with little known about it. It was thought to be extinct for 65 years until its rediscovery in 1970.In 2016 an adult couple was found to the east, in the Caetetus Ecological Station, after six years with no sightings. The total number of individuals is estimated to be around 1000. Some experts believe this to be an overestimate, as recent studies have shown that the average area inhabited by the black lion tamarin is closer to 106 hectares (260 acres) than the previously estimated 66 hectares (160 acres). They are usually found in groups of 4 to 9, living in the secondary and primary forests along the circumference of its home range. On average, the black lion tamarin weighs 590–640 grams (21–23 oz). The diet of the black lion tamarin is seasonal and varies with the habitats it moves through. When the tamarin is in the dryland forest, it usually eats a variety of fruits, whereas in a swampy environment it predominantly feeds on the gum of various trees. In addition to seasonal variation, the black lion tamarin exhibits daily and monthly cycles of food preferences. Independent of the environment it occupies, a tamarin spends long periods each day searching for different types of insects and spiders to feed on. On average, 80% of its time foraging is spent searching for insects, such as by foraging the forest floor. The tamarin's foraging locations are very intentional: it spends extended periods of time looking under dry palm leaves, in loose bark, and in tree cavities, with hands that have specialized fingers for prying. The tamarin also positions itself in trees and scans for insects from above, usually four meters above the forest floor. The black lion tamarin eats the gum and fruit of trees, climbing up to ten meters to reach them and as these are easily found, the tamarin spends 12.8% of its day obtaining them, rather than the 41.2% of the day spent foraging for insects in the high trees. Black lion tamarins mate and have offspring during the spring, summer, and fall months (August to March in Brazil). Females usually have one litter per year, though 20% females produce two litters per year. The mean litter size is two infants. Most mammals produce a 50:50 ratio of males to females. The black lion tamarin population almost always produce a 60:40 male to female ratio.