Landscape-scale grassland structural heterogeneity and disturbance regimes influence swamp deer habitat utilisation across the upper Gangetic plains, India

Large herbivores play a vital role in shaping grassland ecosystems, yet many species face increasing threats from habitat loss, fragmentation, and human disturbance. In northern India, riverine grasslands of the Gangetic floodplains serve as essential habitats for such species, including the swamp deer (Rucervus duvaucelii duvaucelii), a habitat specialist that has experienced severe population declines, especially outside protected areas. We evaluated the structural vegetation composition of grasslands and swamp deer habitat use along the Ganges river, covering both protected regions (Jhilmil Jheel Conservation Reserve and Hastinapur Wildlife Sanctuary) and surrounding non-protected grasslands. Combining field-based vegetation surveys with NDVI-based remote sensing enabled the classification of grasslands into four ecologically significant types structured by Saccharum, Phragmites, and Typha species. Disturbance was prevalent across the landscape, with approximately 77% of grassland plots exhibiting signs of human impact. Pure Saccharum grasslands exhibited the highest disturbance levels, followed by mixed patches, while Phragmites-Typha patches showed the lowest disturbance. Conversely, Phragmites-Typha patches experienced the lowest levels of disturbance. Data from surveys and two radio-collared swamp deer indicated a consistent preference for mixed vegetation types, particularly Saccharum-dominated and Phragmites-Typha mixes, while avoiding heavily disturbed pure Saccharum patches. Seasonal changes in habitat use reflected context-dependent selection influenced by vegetation structure, hydrology, and disturbance regimes. Our results underscore the importance of conserving diverse grassland mosaics and reducing human pressures, especially in unprotected areas to promote the long-term survival of swamp deer and other grassland herbivores within the Gangetic floodplains.