Patterns in avian assemblages on two islands of the Central Nicobar with emphasis on interactions between the endemic Nicobar Bulbul and Red-whiskered bulbul

Abstract

Bird Communities were studied on two islands of the central Nicobar, namely Teressa (Large) and Bompuka (Small) between 16th December 2016 and 15thApril 2017. • This study aimed to understand the patterns in avian assemblages on these islandsand further understand the nature of interaction between Red-whiskered Bulbul and the Nicobar Bulbul • 4 major habitats were identified viz Primary forest, Secondary forest, Plantations, and Grassland based on an exhaustive reconnaissance survey • In total 110 point counts were conducted within these habitats on both the islands • 56 bird species belonging to 30 families were recorded during the study. Teressa had higher species richness than Bompuka • Bird assemblage on Bompuka was a complete subset of Teressa and nested ness was found to be significant (p<O.O 1) • There was distinct segregation within the bird communities of Grassland habitat and the woodland (Primary forest, Secondary forest and Plantation). Within woodland, Plantation was found to be a subset of Secondary forest community • Two endemics, Nicobar Megapode and Andaman Cuckoo-dove were found to be exclusive to Primary forest. Four endemics, Andaman Green Pigeon, Nicobar Bulbul, Nicobar Imperial Pigeon and Long-tailed Parakeet occurred in woodland habitats. White-rumped Munia. Zitting Cisticola. Rosy Starling and Yellowlegged Buttonquail were exclusive to the Grassland habitat • Canopy height and Evenness along vertical strata explained most variation in bird community belonging to Teressa. Nicobar Imperial Pigeon and Nicobar bulbul showed a preference for tall trees that occurred in Primary forest. Birds like Zitting Cisticola and White-rumped Munia showed preference towards Grass cover • In Bompuka, Foliage height diversity (Shannon in CCA plot) and Grass cover explained the maximum variance in the bird community. Although the associations were not found to be strong, species like Zitting Cisticola and Bluetailed Bee-eater were found to associate with Grass cover • This study showed that there was no negative interaction between the Nicobar bulbul and the introduced Red-whiskered Bulbul. Both species showed a differential space-use horizontally, but had overlap in vertical space-use in places where they co-occurred. Further, playback experiments revealed that these species did not respond to each other and no aggression was noted • The importance of Primary forest to the endemics present on these islands was apparent. However, the increasing anthropogenic pressure is of a major concern for these islands, as habitat is being lost to unmonitored logging for wood and construction