Contiguous forest supports higher bird diversity compared to isolated forest: Evidence from forest landscape of Eastern Nepal

Avifaunal diversity can act as a proxy to prioritize areas for conservation, such as Important Bird and Biodiversity Areas (IBAs). Within such priority areas, different forest structures can have contrasting effects on avifauna, and could potentially lead to an overlapping but somewhat different species assemblage. Therefore, we aimed to quantify the relative importance of horizontal forest structures and fragmented habitats i.e., contiguous forest and isolated forest, in harboring avifauna and also understanding the patterns of diversity in different seasons in the Mai Valley IBA of Eastern Nepal. We used a double-observer method to collect bird species lists during repeated visits in winter and spring to an isolated and a contiguous forest area. We used Hill numbers and Hutcheson’s t-test to account for differences in the number of survey points sampled in each forest. The study recorded higher diversity in the contiguous forest compared to the isolated forest. However, the bird assemblage based on foraging and habitat guild were found to be similar between these two forests. Despite the importance of both forests for avifauna, restricted-range species were recorded only in contiguous forest. The ecological integrity of contiguous forests provides a natural habitat with a variety of niches influencing the presence of forest specialists, which might lead to the higher species diversity observed in contiguous forest. Also, the difference in area, and forest management regime could have influenced the diversity difference between the two forest types. We recommend more research on avifaunal assemblage and their habitat to prioritize these critical areas for conservation. Furthermore, considering the role played by contiguous forest in maintaining bird communities, we emphasize the maintenance of forest birds corridors by preserving natural forests and planting native trees in private orchards in the Mai Valley Area.