The purpose of this study was to investigate if there was any species-specific type and structure of sleeping sites of common marmosets Callithrix jacchus and their key determinant. The study was conducted in an urban fragment of the Atlantic forest of north-eastern Brazil, where a group of common marmosets was followed for 488 h. For this purpose we used ad lib observations, performed twice a week, when the animals were entering and leaving the sleeping sites, identified potential predators of the common marmosets through interviews with local people, and identified the trees that provided them with fruit and/or exudate during the study. Five sleeping sites were identified, all invariably in the border of the native forest and the orchard. No predators of common marmosets were seen by local people or recorded during this study, and the sleeping trees were located invariably in the place where there was the highest concentration of feeding trees, regardless of its structure. There was no species-specific type and structure of sleeping places of common marmosets. The key variable defining the choice of a sleeping place was the availability and location of immediate sources of food.

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The purpose of this study was to investigate the population status of the common marmosets, Callithrix jacchus, in one of their main habitats, the northeastern Atlantic forest of Brazil, where only 2% of its original area remains as small and isolated forest fragments, to determine long-term viable populations. The study was carried out in 15 forest fragments, measuring from 3,478.3 ha (the largest) to 6 ha, which were invariably subjected to high human impact. Line transect surveys were carried out between January 2002 and December 2004, along transects measuring from 350 to 4,000 m, between 0500 h and 0900 h. Common marmosets were registered in 73% (n = 11) of the forest fragments, were not recorded in the largest one, the Coimbra Forest, and group sizes varied from 1 to 4 individuals. A negative significant relationship was detected between the size of the fragment and the number of sightings of common marmosets. It is shown that the number of groups of common marmosets dwelling in this highly impacted landscape is nowadays lower than necessary for long-term survival. Additionally, smaller fragments having more groups suggests that they live in total association with humans, which assure their subsistence through the supply of introduced and exotic foods.