<p>Two ecologically similar semi-aquatic herbivores can coexist if they segregate along at least one niche dimension, such as space or time. Urban habitats may constrain this segregation by homogenizing habitats, reducing resource diversity, and altering animal behavior, potentially intensifying interspecific interactions. Coypus (<i>Myocastor coypus</i>) and capybaras (<i>Hydrochoerus hydrochaeris</i>) frequently co-occur in urban wetlands of Argentina and share similar habitat requirements, making them an ideal model to evaluate mechanisms of coexistence under urban constraints. This study examines spatial, temporal, and fine-scale spatio-temporal interactions between coypus and capybaras within a single large gated urban complex composed of multiple residential developments in the Metropolitan Area of Buenos Aires, Argentina. Specifically, we aimed to: (1) assess spatial overlap and patterns of co-occurrence across the complex; (2) quantify overlap in daily activity patterns and its seasonal variation; and (3) evaluate simultaneous spatio-temporal co-occurrence at shared sites and its seasonal dynamics. We found a relatively high degree of spatial and temporal overlap between both species, particularly during warmer seasons when food availability is higher. In contrast, segregation emerged at the fine-scale simultaneous spatio-temporal level, driven by differences in peak activity periods and suggesting avoidance of direct encounters. This pattern is consistent with the competitive exclusion principle and indicates that interference competition may become more pronounced during colder seasons, when resources are limited. Our results highlight how urbanization constrains niche segregation at broad scales while promoting coexistence through subtle temporal and behavioral adjustments within a single, highly modified urban habitat.</p>