Identifying the source population of naturally recolonised rhinoceros (Rhinoceros unicornis) in Laokhowa-Burhachapori Wildlife Sanctuary, Assam, through multidisciplinary methods

Abstract

Megaherbivore population recovery largely depends on restoring connectivity between fragmented protected areas to facilitate natural dispersal, gene flow, and range expansion. The Indian rhinoceros (Rhinoceros unicornis) has recovered from severe population decline in the past, but several populations remain spatially restricted. Recent conservation efforts and the expansion of protected areas in Assam have coincided with natural rhino recolonization in Laokhowa-Burhachapori Wildlife Sanctuary (WLS). This has occurred from nearby regions of Orang NP and Kaziranga NP after the species was locally extinct in the 1980s. Identifying the source population of these recolonised rhinos is crucial for managing this emerging metapopulation. We used non-invasive genetic sampling, genetic assignment and a landscape connectivity model to investigate the origin and potential movement routes of the recolonising rhinos. We identified eight unique individuals from Laokhowa-Burhachapori WLS and assigned them to the potential source population using Bayesian and frequency-based approaches against a reference dataset of 365 individual rhinos across the rhino-bearing areas of Assam. Habitat suitability was modelled using 161 spatially thinned presence points and eight environmental variables. We applied least-cost path (LCP) analysis to assess landscape resistance between protected area nodes. All eight recolonising rhinos were assigned to Orang NP with high Bayesian assignment probabilities (q = 0.97-0.99). The connectivity model identified two least-cost pathways, with the Orang NP-Laokhowa-Burhachapori WLS linkage showing lower landscape friction than the Kaziranga NP linkage. These findings provide genetic evidence that the recolonisation occurred through natural dispersal, most likely from Orang NP, and indicate that recent landscape restoration has re-established the structural connectivity across this floodplain. Maintaining these linkages will be essential to promote natural range expansion and the long-term persistence of Indian rhinoceros in Assam.