Factors affecting the breeding ecology of the globally threatened Lesser Adjutant (Leptoptilos javanicus) in agricultural landscapes of Nepal

Abstract

Many threatened birds use the mosaic of agricultural landscapes for foraging and breeding. Despite the reliance of many species on these habitats, few studies have investigated factors influencing the breeding ecology of storks in agricultural landscapes. We assessed site-level variables (tree height and location of nest tree; human habitation or non-human habitation), colony-level variables (colony size and chicks per nest), and landscape-level variables (area of human habitation, wetland area, and distance to the nearest wetland) to understand the factors influencing the breeding ecology of the globally threatened Lesser Adjutant (<em>Leptoptilos javanicus</em>) across multiple locations in the agricultural landscape of lowland Nepal during 2019–2020. We monitored 65 active colonies that had 206 active nests in five study sites. Two hundred eighty chicks fledged from these colonies, with 13% (n = 41) chick mortality. Most colonies were in agricultural land (51%) and human habitation (28%). Lesser Adjutant colonies located on tall trees such as <em>Bombax ceiba</em> (57%), <em>Haldina cordifolia</em> (11%), and <em>Ficus religiosa</em> (11%); however, these tree species were used much more than their availability on the landscape. Tree height had a significant positive influence on colony site selection and colony size, whereas colony size positively influenced fledgling success. Measured landscape variables did not have significant relationships with breeding success metrics. The agricultural landscapes of lowland Nepal provided important breeding habitat for Lesser Adjutants, and the suitability of sites with colonies related more to site-level and colony-level than landscape-level variables. Increasing urban development of agricultural landscapes is likely the greatest threat to breeding Lesser Adjutants, with the decline of suitable nesting trees being a potential additional threat. Lowland Nepal's agricultural landscapes support significant breeding populations of Lesser Adjutants that had considerable breeding success, underscoring the urgent need to support traditional agriculture that favors large waterbirds.