Breeding ecology of the Asian openbill in eastern Nepal: Larger trees support higher fledgling success.

Colonial nesting waterbirds in agricultural landscapes have historically received limited research attention, especially in South Asia. For example, the Asian openbill (Anastomus oscitans) is a colonial species that extensively utilizes agricultural landscapes, yet there is a notable lack of substantial studies despite increasing urbanization across these landscapes. We investigated the factors affecting the breeding ecology of Asian openbills in eastern Nepal. We used a grid-based approach to locate stork colonies and monitored them throughout the breeding season from May to November for three consecutive years (2020-2022). Altogether, we observed a total of 67 active colonies, comprising 4020 active nests, which successfully fledged a total of 7566 chicks. Additionally, most of the colonies were located within areas of human settlements (40%), followed by community forests (33%) and agricultural land (27%). The Asian openbills primarily preferred large trees, such as Bombax ceiba (72%), for nesting. The mean height of nesting trees was approximately 4 m taller, the diameter at breast height was twice as large, and the canopy cover area was three times greater than that of non-nesting trees. The canopy cover area of trees positively influenced the colony size, while colony size positively influenced the fledgling's success. Our study underscores the significance of large trees in providing sufficient space for accommodating a substantial number of openbill nests and fledglings. These findings have significant implications for conservation efforts to protect large trees along with wetlands and agricultural lands, as crucial measures to ensure the sustainable breeding of this nationally vulnerable species.

Niche segregation, competition, and urbanization.

Urbanization of species is an ongoing process where successful urban colonizers usually obtain large fitness benefits. Mechanisms proposed to explain associations between urbanization and life-history traits are based on behavioral flexibility in food and habitat use and reduced fear responses. We test the novel hypothesis that interspecific competition for proximity to humans is driving urbanization. We recorded the distance during the breeding season to human habitation for 50 pairs of closely related bird species, where one was closely associated with humans while the other species was not. The degree of urbanization was larger as was range size and abundance in the species more closely associated to humans. Flight initiation distance was shorter, and species closely associated with humans were more abundant in ancestral rural habitats. Likewise, species more closely associated with humans reproduced earlier and during longer periods. These results are consistent with the hypothesis that urbanization is promoted by interspecific competition. Resulting isolation by urban habitat may further facilitate contemporary adaptation to urban environments.