Diversity, abundance and community composition of birds in Chitwan Annapurna Landscape, central Nepal

Understanding bird diversity and composition is important for assessing survival, adaptability and extinction risks. This study investigated bird species abundance, richness, seasonal diversity and composition across habitats, seasons and physiographic zones of Chitwan Annapurna Landscape (CHAL) from 2020 to 2021 using point count method. We recorded 458 bird species with higher richness and diversity in winter (n = 365) than summer (n= 299).  This study indicates high diversity of birds (Shannon= 5.54, Simpson= 0.99) and even distribution of species Pielou's Evenness Index (0.90). Species richness and abundance showed seasonal and habitat-specific variations, with wetlands highest in winter (richness: 6.94 ± 0.38, abundance: 23.10 ± 5.65) and croplands in summer (richness: 7.00 ± 0.35, abundance: 13.61 ± 1.10), while forests exhibited stability. Evenness was high across all habitats (0.90 ± 0.01 to 0.95 ± 0.00), with minimal seasonal variation. Diversity indices were highest in cropland during summer (Margalef: 2.33 ± 0.10, Shannon: 1.77 ± 0.06, Simpson: 0.80 ± 0.02) and wetlands during winter (Margalef: 2.19 ± 0.08, Shannon: 1.75 ± 0.05, Simpson: 0.79 ± 0.01), forests had moderate and stable diversity, while grasslands showed low values. We observed 2 globally vulnerable, 5 near-threatened, 2 endangered and 3 critically endangered species. ANOSIM revealed significant community differentiation (p < 0.01) across parameters, with the strongest segregation in physiographic (R = 0.09), followed by seasons (R = 0.06) and habitat types (R = 0.01). CCA showed distinct habitat clusters and strong influence of physiographic zones, with winter and wetland habitats driving species variance. This study revealed substantial differences in bird species across seasons and each habitat offers a distinct ecological niche for bird species. This finding highlights CHAL as hotspots for bird community. This research contributes to the conservation and management of this landscape, aiding in the protection of bird species in Nepal.

Methods
Grids: The entire study area was divided into 9440 grids of size 1×1 km2. Altogether, 514 grids were selected by using sample size determination at a 98% confidence level and 5% margin of error. Among 514 grids, 472 were selected for the study due to inaccessibility to visit the rest of the grids. In each grid, bird species, along with environmental variables, were recorded within 50 m radius.

Point count near the centroid of each grid: During data collection, 1–5 minutes were allocated for adjustment to the location, followed by 20 minutes dedicated to counting birds, observing their habitats, and noting other environmental factors.

Collected birds’ data along with the number of individuals reported, time, and weather conditions by developing a standard data sheet. The calls of the birds were recorded using a recording device for further analysis. The birds were identified by using a field guide book, "Birds of Nepal (Grimmett et al. 2016)." We also consulted with bird experts for the confirmation of birds by using photographs. We also used the Merlin Bird ID app to identify birds by comparing their photographs and sounds.