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.
Hornbill densities in Namdapha
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.
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.
Effects of hunting and logging on seed dispersal
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.
Looking beyond Protected Areas
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.
- Dataset2016Data from: Spatial and temporal variation in hornbill densities in Namdapha Tiger Reserve, Arunachal Pradesh, north-east IndiaDOI: doi:10.5061/dryad.qr068
- Journal Article2015Fruit resource tracking by hornbill species at multiple scales in a tropical forest in IndiaJournal of Tropical Ecology, 31:477-490Download
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The fruit-tracking hypothesis predicts a positive association between frugivores and fruit abundance over space and time.We documented hornbill diets and examined the relationship between fruit abundance and abundance of three hornbill species (Buceros bicornis, Rhyticeros undulatus and Aceros nipalensis) in the Eastern Himalaya from 2009– 2012. The study was carried out at three scales: at the largest scale of the study area (15km2), at the intermediate scale – eight 3-ha patches within the study area and at the smallest scale of individual fruiting trees.Ninety-one per cent of the 64 foraging sightings of the great hornbill were on figs while more than 50% of the foraging sightings of the wreathed (83) and rufous-necked hornbills (87) were on non-fig fruits. At the largest scale, wreathed hornbill abundance and ripe fruit abundance peaked in the non-breeding season. At the intermediate scale, wreathed hornbill abundance was positively associated with non-fig fruit availability while rufous-necked hornbill abundance was negatively associated with non-fig fruit availability. At the smallest scale, great and rufous-necked hornbill abundances were correlatedwith fig and non-fig fruit crop sizes, respectively. The three hornbill species track fruit availability at different scales based on diet, which has implications for their role in seed dispersal.
- Journal Article2015Reduced hornbill abundance associated with low seed arrival and altered recruitment in a hunted and logged tropical forestPLOSOne; DOI: 10.1371/journal.pone.0120062
Logging and hunting are two key direct threats to the survival of wildlife in the tropics, and also disrupt important ecosystem processes. We investigated the impacts of these two factors on the different stages of the seed dispersal cycle, including abundance of plants and their dispersers and dispersal of seeds and recruitment, in a tropical forest in north-east India. We focused on hornbills, which are important seed dispersers in these forests, and their food tree species. We compared abundances of hornbill food tree species in a site with high logging and hunting pressures (heavily disturbed) with a site that had no logging and relatively low levels of hunting (less disturbed) to understand logging impacts on hornbill food tree abundance. We compared hornbill abundances across these two sites. We, then, compared the scatter-dispersed seed arrival of five large-seeded tree species and the recruitment of four of those species. Abundances of hornbill food trees that are preferentially targeted by logging were two times higher in the less disturbed site as compared to the heavily disturbed site while that of hornbills was 22 times higher. The arrival of scatter-dispersed seeds was seven times higher in the less disturbed site. Abundances of recruits of two tree species were significantly higher in the less disturbed site. For another species, abundances of younger recruits were significantly lower while that of older recruits were higher in the heavily disturbed site. Our findings suggest that logging reduces food plant abundance for an important frugivore-seed disperser group, while hunting diminishes disperser abundances, with an associated reduction in seed arrival and altered recruitment of animal-dispersed tree species in the disturbed site. Based on our results, we present a conceptual model depicting the relationships and pathways between vertebrate-dispersed trees, their dispersers, and the impacts of hunting and logging on these pathways.
- Journal Article2015Looking beyond parks: the conservation value of unprotected areas for hornbills in Arunachal Pradesh, Eastern HimalayaOryx, 49:303-311Download
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The loss of tropical forests and associated biodiversity is a global concern. Conservation efforts in tropical countries such as India have mostly focused on state-administered protected areas despite the existence of vast tracts of forest outside these areas. We studied hornbills (Bucerotidae), an ecologically important vertebrate group and a flagship for tropical forest conservation, to assess the importance of forests outside protected areas in Arunachal Pradesh, north-east India. We conducted a state-wide survey to record encounters with hornbills in seven protected areas, six state-managed reserved forests and six community-managed unclassed forests. We estimated the density of hornbills in one protected area, four reserved forests and two unclassed forests in eastern Arunachal Pradesh. The state-wide survey showed that the mean rate of encounter of rufous-necked hornbills Aceros nipalensis was four times higher in protected areas than in reserved forests and 22 times higher in protected areas than in unclassed forests. The mean rate of encounter of wreathed hornbills Rhyticeros undulatus was twice as high in protected areas as in reserved forests and eight times higher in protected areas than in unclassed forests. The densities of rufous-necked hornbill were higher inside protected areas, whereas the densities of great hornbill Buceros bicornis and wreathed hornbill were similar inside and outside protected areas. Key informant surveys revealed possible extirpation of some hornbill species at sites in two protected areas and three unclassed forests. These results highlight a paradoxical situation where individual populations of hornbills are being lost even in some legally protected habitat, whereas they continue to persist over most of the landscape. Better protection within protected areas and creative community- based conservation efforts elsewhere are necessary to maintain hornbill populations in this biodiversity-rich region.
- Book Chapter2015Hope for hornbillsIn: Allison Hegan (Ed.), Endangered Tales.
- Popular Article2014Gardeners of the rainforestSaevus, November 2014, pp. 19-23.
- Thesis2014Seed dispersal by hornbills, conservation status and the consequences of their decline in tropical forests of Arunachal PradeshManipal University, Manipal, Karnataka
- Journal Article2013Spatial and temporal variation in hornbill densities in Namdapha Tiger Reserve, Arunachal Pradesh, north-east IndiaTropical Conservation Science 6:734-748Download
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Asian hornbill populations are declining across their ranges because of hunting and deforestation. Five of the 32 Asian hornbill species occur in north-east India. However, vital information on their abundance from the region remains scanty. Understanding spatiotemporal variation in densities provides crucial information for formulating effective conservation strategies based on species-specific abundance patterns and population trends. We examined spatiotemporal variation in densities of four hornbill species in the Namdapha Tiger Reserve, a site identified as an important site for hornbill conservation in Asia. We collected data through variable-width line transect sampling (effort=842.1 km) in the non-breeding season from 2009-12 to estimate hornbill densities. We had 458 detections of four hornbill species. We have estimated White-throated Brown Hornbill densities (7.9 birds/km2) for the first time throughout its entire range. The mean Rufous-necked Hornbill densities (6.9 birds/km2) were higher than those reported elsewhere. Great (3.9 birds/km2) and Wreathed Hornbill (16.1 birds/km2) densities were comparable with other sites. The peak densities of all hornbill species in November-December are among the highest reported from Asia. Wreathed Hornbill densities showed temporal variation peaking in November-December (68 birds/km2) and drastically declining by March-April (1.3 birds/km2), indicating seasonal altitudinal movement to low elevation areas outside the reserve during the breeding season. Our results underscored the spatial variation in hornbill distribution, with low densities of Great and the White-throated Brown hornbills in higher elevations. Our study demonstrates the global importance of Namdapha for hornbills, given its large area and high densities of four hornbill species.
- Journal Article2009Observations on Rufous-necked Aceros nipalensis and Brown Anorrhinus austeni Hornbills in Arunachal Pradesh: natural history, conservation status and threats.Indian Birds 5: 108-117.Download
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Among the five species of hornbills that occur in north-eastern India, the least studied are the endangered Rufous-necked Hornbill Aceros nipalensis, and the Brown Hornbill Anorrhinus austeni, which has a restricted distribution in India. Based on field surveys conducted in Namdapha National Park, and several forest divisions in eastern Arunachal Pradesh, during 1996–1999 and 2002–2004, I present information on their distribution and relative abundance. I also present some information on diet, flock sizes, canopy levels used, breeding biology, and nesting records for both these species.
- Journal Article2003Foraging patterns of sympatric hornbills in the non-breeding season in Arunachal Pradesh, north-east India.Biotropica 35 (2): 208-218.