Differential habitat use in sympatric species can provide insight into how behavior relates to morphological differences and as a general model for the study of biological adaptations to different functional demands. In Amazonia, closely related sympatric tamarins of the genera Saguinus and Leontocebus regularly form stable mixed-species groups, but exhibit differences in foraging height and locomotor activity. To test the hypothesis that two closely related species in a mixed-species group prefer different modes of leaping regardless of the substrates available, we quantified leaping behavior in a mixed-species group of Saguinus mystax and Leontocebus nigrifrons. We studied leaping behavior in relation to support substrate type and foraging height in the field for 5 months in the Amazonian forest of north-eastern Peru. Saguinus mystax spent significantly more time above 15 m (79%) and used predominantly horizontal and narrow supports for leaping. Leontocebus nigrifrons was predominantly active below 10 m (87%) and exhibited relatively more trunk-to-trunk leaping. Both species preferred their predominant leaping modes regardless of support type availability in the different forest layers. This indicates that the supports most commonly available in each forest layer do not determine the tamarins' leaping behavior. This apparent behavioral adaptation provides a baseline for further investigation into how behavioral differences are reflected in the morphology and species-specific biomechanics of leaping behavior and establishes callitrichid primates as a model well-suited to the general study of biological adaptation.