OCCUPANCY AND DISTRIBUTION PATTERN OF OWLS IN ANDAMAN ISLANDS WITH SPECIAL REFERENCE TO COMMUNITY ASSEMBLY RULES

Abstract

There is a laxity of knowledge in taxonomically well recognized species, which did not gain adequate attention from conservation biologists and are prone to extinction. Owls are one of such avian nocturnal predators. Due to their nocturnal and conspicuous behaviour many of the avian community studies neglecting owls to incorporate in them. Considering these facts, studies on owl species ecology is prerequisite for the conservation. So, this thesis is an attempt to develop such base line information on owls with two broad objectives: (1) to assess the relative abundance and occupancy of owls in the Andaman Islands and (2) to evaluate various species assembly rules in offshore islands using owls as model organism. To achieve these objectives, I did a survey with an aim to elucidate the environmental gradients (such as land-cover types, logging intensity) that influence the distribution and abundance of owls in the Andaman Islands. In addition, I also assessed the perception of local people about owls and effect of human activities on roosting owls using experimental and evidence-based study. I also employed Hierarchical multi-scale sampling strategy to estimate large-scale (sampling unit level - Ψ) and small-scale (survey station level - θ) occupancy using multi-detection methods (p). I modelled the occurrence of each species of owls as a function of island characteristics using the presence-absence of owls and a set of abiotic and biotic variables of 73 offshore islands. Finally, dispersal-driven assembly rules of the five owl species were tested with the same offshore islands surveyed. EcoSim v. 7.0 was used to test the Diamond’s assembly rules (1st, 2nd and 5th rules) using two statistical indices viz., C-score and number of unique species combinations. NeD and Nestedness Temperature Calculator were used to test nestedness. Overall, this study provided first-hand information about the owls’ distribution, their threat, ecological requirements, and the dispersal patterns in Andaman archipelago. It also helped to identify the critical island characteristics to ensure the avian population. The continued alteration of evergreen forests, extraction of minor products (for example: cane) and logging associated understory clearings might bring these endemic species’ survival to an end.