Folia Primatol 1991;57:102-105 © 1991 S. Karger AG. Basel 0015-5713/91 /0572-0102S2.75/0 Field Observations of Goeldi’s Monkey, Callimico goeldii, in Northern Bolivia Hannah Buchanan-Smith Department of Psychology, University of Reading, UK Key Words. Goeldi’s monkey • Callimico goeldii • Social organisation • Field study ■ Group size • Monogamy Introduction Goeldi’s monkey, Callimico goeldii, is a small diurnal South American primate whose geographical range extends from south-eastern Peru and northern Bolivia to southern Colombia [1,2]. There is some con troversy about social organisation of Callim ico in the wild. It has been stated that the basic group size is usually a family of 2-4, i.e. an adult male, an adult female, possibly with a juvenile and/or an infant [3], This interpretation arose from brief observations [4] and from data collected from interviews in Colombia, Peru and Bolivia [5], However, the only two detailed field studies on the behaviour of Callimico in Bolivia [2, 6-8] indicate that groups may contain as many as 9 individuals, including infants. This paper reports further field observations of Callim ico in northern Bolivia. Methods Observations were made between November 8 and 14, 1987, in the Pando Department of north-west Bo livia. The study site, called Planchón, was south-west of the Department’s capital, Cobija (11° 11 ’ S, 68 ° 42’ W; fig. 1) Cobija has a marked dry season from June to September. The annual rainfall in 1987 was 1,983 mm, with 359 mm falling in November. The study area con sisted mainly of primary forest, with small patches of scrub forest with bamboo which occurred naturally. Eight other primate species lived sympatrically at the study area: Pithecia irroraw [9], Callicebus cupreus, Aloualta seniculus, Cebus albifrons, Cebus apella, Aotus trivirgatus, Saguinus fuscicollis weddelli and Saguinus labiatus labiatus. Further details of a study site nearby are provided elsewhere [10]. Initially, my guide (Edilio Nasciemento) and I made a general prospecting survey of the forest. Once Callimico had been located, we returned specifically to that area in an attempt to locate the group again. Checksheet data were collected on the time and dura tion of sightings, forest location, on-going activity, the number of animals seen, the height in the forest and the distance to the nearest other primate species.