Composition and Structure of Mixed Species Bird Flocks and Their Seasonal Changes in Montane Forest Habitats of Horton Plains National Park, Sri Lanka

Abstract

Mixed-species flocks are the frequent phenomenon in many habitats worldwide. The composition, structure and seasonal changes of mixed species bird flocks were observed in the tropical montane cloud forest habitats of Horton Plains National Park from December 2017 to October 2018. Line transects of 1000m length and 20m width were surveyed in three selected study sites of this park. A total of 2,140 individual birds belonging to 16 species were recorded in MSBFs during the study. Annual average flock size and species richness values were 25.8 ± 8.3 and 6.9 ± 1.6 respectively. The canopy height utilization significantly differed among these 16 species observed. There were nine species who acted as leading species in the MSBFs. Sri Lanka Orange-billed Babbler Turdoides rufescens was the most specific leading species. The average number of flocks was relatively higher in the Southwest monsoon season and lower in 1st inter monsoon season when compared to other seasons. A significantly higher flock size and a species richness were recorded in 2nd inter monsoon season and significantly lower values were recorded in the 1st inter monsoon season. There were no significant differences on average flock number in each study site and between the seasons. The findings indicate an even distribution of MSBFs in the HPNP without any seasonal barrier. The 2nd Inter monsoon season (October–November) can be identified as the most suitable period for observations of MSBFs. Conservation measures should be integrated in ecotourism activities especially during the holidays.