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

  • Great Hornbill diet is chiefly comprised of figs. A rapid survey indicated that locals had not seen these species in forests around there villages for more than five years likely indicating local extirpation

  • Wreathed Hornbills visited the Hornbill Plateau of Namdapha TR in large numbers during the non-breeding season (October - April). Their densities in November - December were as high as 65 hornbills per sq. km on the Hornbill Plate

  • The dispersed seed arrival rate of just five of large-seeded hornbill food plants was as high as 3000 seeds per day per sq. km justifying hornbills being called as "Farmers of the forest"

  • Rufous-necked Hornbill density in Namdapha was 6 birds per sq. km. With more than 1200 sq.km of suitable habitat, Namdapha harbors a large population of this species

  • Hornbills are hunted for their meat and body parts across different sites in Arunachal Pradesh.

  • Our large-scale and intensive survey indicated that Rufous-necked Hornbill abundance was higher inside Protected Areas as compared to outside


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 20river dihing 20river 20valley 20at 20firmbase

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. 

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.

Flock 20of 20wreathed 20hornbills 20in 20pakke kalyan 20verma

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.


Hunting of important seed dispersers like the Rufous-necked hornbill, can alter key ecosystem processes

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.

Rohit nokreknp garohills

Vast tracts of forest lie outside Protected Areas in Arunachal



  • Critical Ecosystems Partnership Foundation (CEPF) & ATREE
  • International Foundation for Science (IFS), Sweden
  • Rufford Small Grants Foundation, UK


  • Dataset
    Data from: Spatial and temporal variation in hornbill densities in Namdapha Tiger Reserve, Arunachal Pradesh, north-east India
    DOI: doi:10.5061/dryad.qr068
  • Journal Article
    Fruit resource tracking by hornbill species at multiple scales in a tropical forest in India
    Journal of Tropical Ecology, 31:477-490

    PDF, 793 KB

    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 Article
    Reduced hornbill abundance associated with low seed arrival and altered recruitment in a hunted and logged tropical forest
    PLOSOne; 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 Article
    Looking beyond parks: the conservation value of unprotected areas for hornbills in Arunachal Pradesh, Eastern Himalaya
    Oryx, 49:303-311

    PDF, 383 KB

    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 Chapter
    Hope for hornbills
    In: Allison Hegan (Ed.), Endangered Tales.
  • Popular Article
    Gardeners of the rainforest
    Rohit Naniwadekar, Sartaj Ghuman
    Saevus, November 2014, pp. 19-23.
  • Thesis
    Seed dispersal by hornbills, conservation status and the consequences of their decline in tropical forests of Arunachal Pradesh
    Manipal University, Manipal, Karnataka

    PDF, 9.62 MB

  • Journal Article
    Spatial and temporal variation in hornbill densities in Namdapha Tiger Reserve, Arunachal Pradesh, north-east India
    Tropical Conservation Science 6:734-748

    PDF, 642 KB

    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 Article
    Observations on Rufous-necked Aceros nipalensis and Brown Anorrhinus austeni Hornbills in Arunachal Pradesh: natural history, conservation status and threats. 
    Indian Birds 5: 108-117.

    PDF, 789 KB

    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 Article
    Foraging patterns of sympatric hornbills in the non-breeding season in Arunachal Pradesh, north-east India. 
    Aparajita Datta, G.S. Rawat
    Biotropica 35 (2): 208-218.

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