The composition of mixed-species flocks of birds in and around Chitwan National Park, Nepal

Eben Goodale,Kamal Raj Gosai

doi:10.1186/s40657-021-00292-3

Abstract

BackgroundMixed-species flocks (MSFs) have been well sampled in the South Asia, but there has been as yet surprisingly little work on MSFs of Nepal, despite a diverse and well-studied avifauna. We surveyed MSFs in two forest types in and around the Important Bird Area of Chitwan National Park in Nepal, between 150 and 800 m a.s.l., to provide a first description of the composition of MSFs in this area. We also aimed to understand which species should be considered ‘nuclear species’, important to forming MSFs or leading them forward.ResultsIn total, we collected records on 222 MSFs that included 100 species, and 6097 individuals. The MSFs were similar to worldwide patterns in being dominated by leaf-gleaning, non-terrestrial insectivores. However, the MSFs were more dominated by canopy species than usual, and did not have a clear gregarious, understory leading species. Rather drongos (Family Dicruridae) and minivets (Family Campephagidae, Genus Pericrocotus) acted as leaders, and a cluster analysis of composition showed one group of large body size MSFs particularly characterized by the presence of the Greater Racket-tailed Drongo (Dicrurus paradiseus).ConclusionsDrongos are known to provide both costs and benefits to other flock participants: they are aggressive birds that can steal food, and manipulate other species with their vocalizations, but at the same time they are ‘sentinel species’ that produce information about predation risk other species can use. This study demonstrates that drongos can be considered nuclear species for some types of MSFs, despite the potential costs of their presence. MSFs led by sentinel species thus may form in Asia, as well as in the Neotropics.

Highlights

Mixed-species flocks (MSFs) have been well sampled in the South Asia, but there has been as yet surprisingly little work on MSFs of Nepal, despite a diverse and well-studied avifauna
We initially aimed to describe MSFs inside and around Chitwan National Park, Nepal’s oldest national park and an Important Bird Area for the country (Inksipp et al 2016), surveying the two most important forest types of the areas (CNP 2015)
MSF size and composition During the study period, we encountered a total of 222 MSFs (162 in Sal Forest (SF) and 60 in riverine forest (RF)), including 100 species (93 species in SF, 75 in RF) and 6097 individuals (4509 in SF, 1588 in RF)

Summary

Introduction

Mixed-species flocks (MSFs) have been well sampled in the South Asia, but there has been as yet surprisingly little work on MSFs of Nepal, despite a diverse and well-studied avifauna. Mixed-species flocks of birds (MSFs) reach their peak of diversity in forested habitat, where they are found, year-round in the tropics, and in migration and winter in temperate regions (Greenberg 2000; Goodale et al 2017). Nuclear species tend to be gregarious and to engage in conspicuous calling and otherwise active behavior (Hutto 1994; Goodale and Beauchamp 2010; Pagani-Nunez et al 2018). Because they have an important conspecific audience in MSFs, which may include kin or mates, it is thought these species are likely to produce costly information such as alarm calls (Goodale et al 2020)

Objectives

Methods

Results

Discussion

Conclusion