Diversity and factors shaping bird species abundance in a hilly region of Makawanpur district, Nepal

Birds play a major role in seed dispersal through pollination, nutrient cycle, and pest control. Understanding contributing factors (both ecological and anthropogenic), and their influence on the diversity of birds is crucial to sustain ecosystem balance and prosperity. We investigated the diversity and associated factors of bird species in a hilly region of Makawanpur district, Nepal. The field survey was conducted throughout the winter season (December-February 2021) using the point count method (radius=30 m). Within the study area, we established 22 sampling plots between the elevations of 431 m above sea level to 2503 m asl. We used generalized linear model to investigate the role of different factors in shaping the species richness pattern. A total of 1860 independent observations of 172 bird species were made during the study where the majority of the species were common and belonged to order Passeriformes. We observed a decrease in bird diversity with increase in elevation. The quantity of invasive plant species (IAPS) cover, disturbance and the slope of the area substantially impacted the diversity of bird species. Research on diversified bird species and their associations with many factors require a more detailed and long-term survey to investigate more species as well as other patterns and processes throughout the elevational gradient.

Methods
We implemented point count survey using direct observation method in the morning (7:00am – 11:30am) and in the evening (3:00pm – 5:00pm) at every 100 meters of elevation (Bibby et al., 2000; Dieni & Jones, 2002; Sarkar et al., 2009). The lowest elevational limit for the survey was Rapti riverbank near Hetauda city (431 m asl (above sea level)) while the highest elevational limit Simbhanjyang at 2503 m asl. Bird observations and sounds within a 30-meter radius were recorded from a fixed position in the center (Bötsch et al., 2018).