RESUMO
It is common that neighboring groups of the same species use some of the same areas, resulting in home-range overlap. Areas between the home ranges of neighboring groups not used by either group (no-use zone or NUZ) are rarely reported. Here, we report the existence of a NUZ between the home ranges of two Geoffroy's spider monkey groups, and examine its spatial changes over time and the ecological and behavioral underpinnings of such phenomenon. Although its size and location changed between 2017 and 2022, the NUZ was always present. We did not find any differences in the vegetation structure and composition between the NUZ and the ranging areas and in the monkeys' activity patterns between areas adjacent to the NUZ and the other parts of the ranging areas. The number of monkey vocalizations was lower and subgroup size was smaller (although the number of males did not differ) in areas adjacent to the NUZ than in the other parts of the ranging areas. Both changes possibly reflect the tendency to conceal their presence to the neighboring group. Our findings contribute to the understanding of primate space use and highlight the need to focus on the areas delimiting home ranges.