The blond capuchin (Sapajus flavius) is an Endangered species of capuchin monkey largely confined to Atlantic Forest fragments in northeastern Brazil, where dispersal is restricted, and resources are limited. In this thesis, I investigated how the spatial cohesion and group movements of blond capuchins were affected by the conditions of the forest fragment they inhabited. My first manuscript (Chapter 2) focused on forest strata use (for age/sex classes), and group cohesion according to the strata used. My second manuscript (Chapter 3) looked at group movement and leadership in age/sex classes. My study site was a 90 hectare forest fragment located on the border of the states of Paraíba and Pernambuco in Brazil (7°52'85,2"S; 34°96'29,4"O), with a group of ~120 blond capuchins. My collaborators and I collected 633 group scans samples, with 15119 individual observations (October 2021 to July 2022), recording age, sex, location and behaviour of each individual. I found that capuchin use of forest strata varied among age/sex classes, a finding that suggests behavioural adjustments to avoid direct competition in this small fragment. I found that capuchin group movement could be characterized as two waves, with adults in the front wave and juveniles in the back wave, a finding that suggests adults reach preferred foods before juveniles. My work contributes to our understanding of how capuchins use forest fragments and underscores the need for further research in forest fragments to better inform conservation practices for this and other threatened primate species, and the biodiversity of the Atlantic Forests.