Wied's Marmoset is a New World monkey that lives in lowland and sub-montane humid forest, seasonal rain forest, and white sand piaçava forest of eastern Brazil. They are also known to use cacao plantations which are shaded with some native trees remaining from the original forest, and secondary growth forest in abandoned rubber plantations. They eat fruits, flowers, nectar, plant exudates (gums, saps, latex) and animal prey (including frogs, snails, lizards, spiders and insects). They gouge trees trunks, branches and vines of certain species to stimulate the flow of gum, which they eat, and in some species form a notable component of the diet. Since these are harvested from the middle and lower part of the forest, they often travel and forage in the company of the golden-headed lion tamarin, which is also foraging in the canopy. The coloring of Wied's marmoset is mostly black, with white markings on cheeks and forehead. It has rings on its tail and black tufts of fur coming out of its ears. They are distinguished from the other monkeys of the New World by their small size, modified claws rather than nails on all digits except the big toe, the presence of two as opposed to three molar teeth in either side of each jaw, and by the occurrence of twin births. Unlike other marmosets, they lives in groups consisting of 4 or 5 females and 2 or 3 males (plus children). They are matriarchal, and only the dominant female is allowed to mate. They are highly social, spending much of their time grooming. They have individually distinctive calls, and also communicate through gestures and olfactory markings. The groups defend home ranges 10-40 hectares, the size depending on availability and distribution of foods and second-growth patches. They are currently listed as Near Threatened as they are believed to have experienced a decline in the order of 20-25% over the past 18 years primarily as a result of habitat loss. They are also eaten by birds of prey (the harpy eagle, the gray hawk, the roadside hawk and the white-tailed hawk), felines (the jaguar, jaguarundi and ocelot) and snakes. Since it is rather adaptable to anthropogenic disturbance, declines are unlikely to be such that the species would require listing in a threatened category.