Population Size and Structure of the Common Eland in Omo National Park, Southern Ethiopia

Omo National Park in southern Ethiopia harbors a critical yet increasingly threatened population of the common eland (Tragelaphus oryx), one of Africa’s largest antelopes. Facing pressures from habitat fragmentation, poaching, and agro-pastoral encroachment, this population’s ecology remains poorly understood. We conducted the first seasonally explicit assessment of eland abundance, spatial distribution, and demographics in the park using systematic line-transect distance sampling across 67 transects (totaling 402 km) during the 2024/2025 wet and dry seasons. Our results reveal a highly dynamic population driven by seasonal resource availability. Eland abundance increased significantly by 150% from the dry season (1,024 individuals; 95% CI: 674–1,555) to the wet season (2,568 individuals; 95% CI: 1,839–3,585), non-overlapping confidence intervals confirming a substantial seasonal influx. Spatially, the Sai Plain functioned as a critical dry-season refugium (61% of sightings), while Tenigne and Elilbaye experienced 4-to-6-fold increases in density during the wet season. This seasonal pulse was mirrored in demographic and social structure: the population exhibited a female-biased (adult male: female ratio ≈ 1:1.4 – 1.5) and significantly higher proportion of calves in the late dry season (21.5% vs. 2.4%; χ² = 41.3, p < 0.001), while social groups shifted from small, fragmented units in the dry season to large aggregations in the wet season (W = 24, p = 0.012). These findings confirm that Omo National Park functions as a dual-role ecosystem: a dry-season stronghold and a regional wet-season resource. This underscores the park’s importance for eland conservation but also highlights its vulnerability to threats that disrupt seasonal movements and habitat connectivity. Our study provides a crucial baseline for long-term monitoring and emphasizes the urgent need for landscape-level management strategies that protect both the park’s core dry-season habitats and the broader corridors essential for the species’ long-term persistence.