The effects of climate and land use change on the potential distribution and nesting habitat of the Lesser Adjutant in Nepal

Abstract

Climate change and land use change pose a threat to the world's biodiversity and have significant impacts on the geographic distribution and composition of many bird species, but little is known about how they affect threatened large-sized waterbird species that rely on agricultural landscapes. To address this gap, we investigated how climate and land use changes influence the distribution and nesting habitats of the globally vulnerable Lesser Adjutant (Leptoptilos javanicus) in Nepal. Between 2012 and 2023, we collected distribution data from 24 districts and nesting site information from 18 districts. In a nation-wide breeding survey conducted in 2020, we documented a total of 581 fledglings from 346 nests in 109 colonies. The ensemble model predicted a current potential distribution of 15% (21,637 ​km2) and a potential nesting habitat of 13% (19,651 ​km2) for the species in Nepal. The highest predicted current suitable distribution and nesting habitat was in Madhesh Province, while none was predicted in Karnali Province. The majority of this predicted distributional and nesting habitat falls on agricultural landscapes (>70%). Our model showed a likely range expansion of up to 15% (21,573 ​km2) for the distribution and up to 12% (17,482 ​km2) for the nesting habitat under SSP5–8.5 scenarios for the 2070s. The range expansion is expected to occur mainly within the current distribution and breeding range (Tarai and some regions of Siwalk), particularly in Lumbini and Sudurpashchim provinces, and extend to the northern portions (Siwalik and Mid-hill regions) in other provinces. However, the current Protected Areas and Important Bird and Biodiversity Areas are inadequate for providing optimal habitats for the species. Although the model suggests range expansion, the use of such novel habitats is primarily contingent on the availability and protection of large-sized trees (particularly Bombax ceiba, observed in 65% of colonies) in agricultural regions where nesting occurs. Therefore, our research suggests that agricultural landscapes should be prioritized in management plans for the conservation of the Lesser Adjutant in Nepal.