Movement and space-use strategies of a vulnerable wetland deer under environmental and human pressures

Context Understanding large herbivore space use is central to landscape ecology, particularly in human-modified landscapes where movement is increasingly constrained. Neotropical cervids are underrepresented in movement studies, limiting our ability to integrate their spatial behavior into landscape planning and conservation. Objectives We provide the first evaluation of how marsh deer ( Blastocerus dichotomus ) organize space use and movement across a fragmented wetland landscape. Specifically, we examined whether distinct movement phases differ in their spatial and temporal patterns and how sex and post-release conditions influence these patterns. Methods We analyzed GPS tracking data from 18 adult marsh deer monitored between 2015 and 2024 in the Paraná River Delta, Argentina. Individual trajectories were segmented into distinct movement phases, and space use and activity patterns were evaluated across spatial and temporal scales. Results Marsh deer consistently structured their movements into four phases: home ranges, excursions, stepping stones, and dispersals. Home ranges accounted for most space use, indicating strong site fidelity within the landscape. Excursions were common and generally short, contrasting with dispersals that were infrequent and covered longer distances. All rehabilitated individuals performed non-resident post-release movements but eventually established home ranges similarly to free-ranging deer. Stepping stones, although transiently occupied, enabled longer-distance excursions and dispersals across fragmented areas in the landscape and connected otherwise isolated residence zones. Activity patterns were predominantly crepuscular, varied seasonally, and differed between sexes. Conclusions Our findings reveal that marsh deer navigate fragmented wetland landscapes through a diversity of movement tactics shaped by sex and individual history, and highlight that characterizing the full spectrum of movement is key for identifying spatiotemporal ecological patterns and requirements, and for informing wildlife conservation in human-modified landscapes.