Understanding impacts of hornbill loss on plants
Final report submitted to Arunachal Pradesh Forest Department, Itanagar, Arunachal Pradesh towards completion of the research project titled “Understanding Impacts of Hornbill Loss on Plants”.

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While large avian frugivores are known to be key dispersers for large-seeded plants, their role in the wider plant-disperser networks is still poorly known. In this study, we evaluate the role of large avian frugivores in plant-disperser communities using network and seed dispersal effectiveness approaches in a tropical forest site in north-east India. We systematically-collected tree watch data from 46 plant species, representing 85 percent of typically bird-dispersed plant species, spanning over 2055 h. We found that the plant-disperser community was modular with a distinct community of large-sized seed plants and frugivores. While intermediate-sized birds such as barbets and bulbuls were the most connected, large-sized dispersers such as hornbills and Imperial-pigeons were moderately well-connected. Imperial-pigeons consistently fed on large-sized fruits, highlighting their importance for dispersal of large-seeded plants. In addition to frugivore-fruit size matching, frugivore dietary choices might play an important role in governing the organization of modules. There was a gradient in qualitative and quantitative roles played by different dispersers, with hornbills removing significantly larger number of fruits and consistently swallowing larger proportions of fruits as compared to other avian groups. Under simulated extinction scenarios, observed networks were far less resilient to disperser loss along a gradient of body size from large to small as compared to extinctions that were random or based on rarity. Given the paucity of information on plant-disperser networks from the South Asian region and reported local extinctions of large frugivores like hornbills, this study is important in highlighting that loss of large avian frugivores might have irreplaceable quantitative and qualitative damages to plant communities.

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