Avain Diversity along Urbanization Gradient of Butwal Sub- Metropolitan City, Nepal

Abstract

Global population shift from rural to urban areas intensifies the urbanization which causes changes in the species composition. Butwal Sub-Metropolitan City in the central lowland Nepal is also facing the rapid changes in land use and land cover, due to urbanization. In this regards, this study was undertaken in the Butwal Sub-Metropolitan City aiming to know the effects of urbanization on avian diversity. The area was categorized as urban and suburban on the basis of NDVI (Normalized Difference Vegetation Index) value, the median value taken as the threshold for the demarcation. Altogether, 8 transects (4 in urban and 4 in suburban

areas) each of 2 km length were deployed. Point count stations were positioned at every 200 m interval along transects. Avian surveys were conducted during the winter and post monsoon seasons of 2020. The avian community structure in the study area was characterized. The associations of avian richness and abundance with NDVI as the proxy of productivity and human footprint data as the proxy of human disturbance were established. Overall, 69 bird species were recorded from 33 families under 14 orders, where Passeriformes was the most dominant order, while insectivores was the most dominant feeding guild. Species richness was higher in winter than in post monsoon. The suburban sites had higher bird diversity and richness than urban sites. This study also illustrated rural– urban gradient effect, supporting the intermediate disturbance hypothesis. Vegetative cover showed positive effects on species richness; on the contrary, human pressure showed negative effects on bird species richness. Temperature and precipitation influenced the avian species richness and abundance. This study clearly demonstrates the importance of vegetative cover and urban greenery for checking the species decline in urban areas, thus, urban policy makers should focus on increasing green spaces in and around the city.