Hornbill seed dispersal and conservation

This project aimed to understand how different hornbills track fruits over space and time, what role do they play as seed dispersers and the impacts of logging and hunting on hornbills and seed dispersal. 

The study was mainly carried out in Namdapha Tiger Reserve  and the adjoining forests from 2008 - 12

Seed dispersal by frugivores is an important mutualistic interaction in tropical forests. As the largest avian frugivores in Asian forests, hornbills are a functionally important group. This study aimed to understand how different hornbill species track fruits over space and time, what role they play as seed dispersers and the impacts of logging and hunting on hornbills and seed dispersal. The study was conducted between 2008 and 2012 and was part of doctoral work of research scholar Rohit Naniwadekar. Research was conducted in the Namdapha Tiger Reserve and the Miao Reserved Forests, Changlang district, Arunachal Pradesh. The study area is part of the Eastern Himalaya Biodiversity Hotspot.

Namdapha comprises five species of hornbills, the Great hornbill, Wreathed hornbill, Oriental Pied hornbill, Rufous-necked hornbill and the White-throated Brown hornbill. Information on their abundance from the region remains scanty. We measured the densities of four of the hornbill species in Namdapha and examined how these species vary in space and time. We collected data for four years (2009-12) in the non-breeding season to estimate hornbill densities. 

Great and Brown Hornbill densities were higher in lower elevations while Rufous-necked Hornbill densities were similar in space and time. Wreathed Hornbill densities showed high temporal variation peaking in winter and declining prior to the breeding season.Our work established a baseline for hornbill densities from the region and demonstrates the global importance of Namdapha for hornbills, given its large area and high densities of four hornbill species.

Logging and hunting are two major threats to the survival of wildlife in the tropics. The study  examined how sympatric hornbill species track resources, the relationship between hornbills and their food plants, its consequences for seed dispersal and how this relationship gets altered due to threats like logging and hunting. The three large hornbill species (Great, Wreathed and Rufous-necked Hornbill) consistently tracked either ripe fig or non-fig fruit availability in accordance with the representation of the two fruit types in their diets. However, while Wreathed Hornbills tracked fruits at the largest (study area) and intermediate scale (sites within study area), the Great and Rufous-necked tracked fruits at the scale of the fruiting tree. Hornbills were the most important visitors on large-seeded tree species.

We found that hornbill abundance was positively related to the abundance of food plants they depended on. We also found that areas with higher hornbill abundance showed higher seed arrival. This cycle has important implications for recruitment of hornbill food plants. However, this relationship was negatively affected by logging and hunting. Sites with logging and hunting showed reduced abundance of hornbill food plants, hornbills, dispersed seeds and altered recruitment of food plants compared to the unlogged and less hunted sites.

Conservation efforts in India have historically focused on state-administered national parks and wildlife reserves. However, vast tracts of forest lie outside these areas. We assessed the value of forests outside Protected Areas in Arunachal, as key habitats for hornbills. Surveys across Arunachal Pradesh showed that while some hornbill species had higher abundances inside Protected Areas than outside, most species continued to be present at lower abundances outside. This finding underscores the importance of conserving larger forest landscapes, which encompass a larger area in the state than Protected Areas.