A reassessment of the Red List status of several Asian hornbill species

BirdLife is currently undertaking a review of the Red List status of forest dependent species following analyses of forest loss carried out by Tracewski et al. (2016) (see background forum topic here). A subset of Asian hornbill species come out of this analysis as potentially quite highly impacted by deforestation, and hunting may be adding to declines in these species; especially as deforestation makes more forest accessible for hunters (see Kinnaird and O’Brien 2007).

Hornbills are hunted for a range of reasons (see Kinnaird and O’Brien 2007); be it consumptive (as food or medicines), decorative (e.g. to make decorative items out of their ‘ivory’ casques or their feathers being used in traditional dress), the pet trade or persecution. Kinnaird and O’Brien (2007) estimate that at least 67% of hornbill species in Asia are hunted, and that any harvesting over 5% of the standing biomass will lead to local declines or disappearance (for a 2kg species occurring at 1 pair per km2). Therefore, not only is hunting widespread but it has the propensity to be having a severe impact on some Asian hornbill species, although clear figures about the impact of hunting on individual hornbill species are scarce.

One species where hunting is considered to be having a major impact is Helmeted Hornbill (Rhinoplax vigil) (see Beastall et al. 2016). In 2015 Helmeted Hornbill (Rhinoplax vigil) was uplisted from Near Threatened to Critically Endangered because of the potential threats from deforestation, and importantly from the high hunting pressure on this species due to the illegal trade of its  unique solid casque, which was suspected to be rapidly increasing and spreading across its range. It has also been suggested that the high demand for the Helmeted Hornbill’s casque may additionally be impacting other hornbill species, as poachers hunting for Helmeted Hornbills may shoot other large hornbill species either by accident or to make sure they don’t miss the opportunity to get hold of their target species (R. Wirth in litt. 2017). Therefore, it seemed appropriate to assess these species separately from the general deforestation topic.

When assessing the species contained within this topic, each species was re-assessed against all Red List criteria. All of these species have a range size that far exceeds the thresholds for Vulnerable under criterion B, and to the best of our knowledge no full quantitative analysis of the probability of extinction has been conducted for any species and so they cannot be assessed against criterion E. Of the species within this topic, only Great Hornbill (Buceros bicornis) has a population size estimate, which is thought to approach but not meet the threshold for Vulnerable under criterion C. All other species have not had their population size estimated, but are currently not thought to approach the threshold for Vulnerable under criterion C or D. Therefore, this topic will focus on criterion A (population reduction), although any comments regarding clearer estimates of population size for these species would be welcome.

As criterion A requires an assessments over a 3 generation period, we present for each species a) the % of forest habitat within the species range that was lost between 2000 and 2012 (per Tracewski et al. [2016]), b) the three-generation period based on generation lengths held in current Red List assessments for each species, and c) the extrapolated % decline as a result of forest loss over three generations assuming continued habitat destruction. The potential impact of hunting is then taken into account for each species, and a new Red List status is proposed.

 

Wrinkled Hornbill (Rhabdotorrhinus corrugatus) – Current listing NT A2c+3c+4c

  • % forest lost within range 2000-2012 = 18.3%
  • Three-generation period = 57 years
  • Extrapolated % decline over three generations = 61.7%

In addition to the generic threat of hunting, and the potential for other large hornbills to be taken as ‘bycatch’ by hunters targeting Helmeted Hornbills, this species is intolerant of degraded or secondary habitat. Therefore, the rate of decline is potentially even greater than that of forest loss. It is tentatively suspected that the overall rate of decline would still fall in the range 50-79% over three generations, and so it is proposed that the species be listed as Endangered under criteria A3cd+4cd.

 

White-crowned Hornbill (Berenicornis comatus) – Current listing NT A2c+3c+4c

  • % forest lost within range 2000-2012 = 13.4%
  • Three-generation period = 57 years
  • Extrapolated % decline over three generations = 49.6%

While this species may be tolerant of some habitat degradation, the rate of habitat loss is exceptionally close to the threshold for Endangered. Therefore, given the potentially additional generic threat of hunting to Asian hornbills, and the potential for other large hornbills to be taken as ‘bycatch’ by hunters targeting Helmeted Hornbills, it may be precautionarily suspected that declines over three generations may fall into the range 50-79%. Hence it is proposed that the species be listed as Endangered under criteria A3cd+4cd.

 

Rhinoceros Hornbill (Buceros rhinoceros) – Current listing NT A2c+3c+4c

  • % forest lost within range 2000-2012 = 11.8%
  • Three-generation period = 55.2 years
  • Extrapolated % decline over three generations = 43.8%

In addition to the impact of forest loss, this species is known to be impacted by hunting, with the species being caught for food, trade and the use of body parts in ceremonial dress (Kemp and Boesman 2017a). The potential that other large hornbills are being taken as ‘bycatch’ by hunters targeting Helmeted Hornbills has also been suggested. The rate of decline due to hunting alone is uncertain, but given the high rate of habitat loss, the species may at least warrant uplisting to Vulnerable under criteria A3cd+4cd (30-49% decline over three generations), and potentially could warrant listing as Endangered under the same criteria.

 

Black Hornbill (Anthracoceros malayanus) – Current listing NT A2c+3c+4c

  • % forest lost within range 2000-2012 = 18.1%
  • Three-generation period = 27.6 years
  • Extrapolated % decline over three generations = 36.7%

In addition to the generic threat to Asian hornbills of hunting, this species’ preference of flat lowland forest means that it may be particularly impacted by habitat loss (Kemp et al. 2017a). Given the extrapolated % decline over three generations due to forest loss, it is therefore suspected that the overall rate of decline for this species would fall in the range 30-49% over three generations. Thus it is proposed that this species be uplisted to Vulnerable under criteria A3cd+4cd.

 

Wreathed Hornbill (Rhyticeros undulatus) – Current listing LC

  • % forest lost within range 2000-2012 = 8.0%
  • Three-generation period = 57 years
  • Extrapolated % decline over three generations = 32.8%

This species is considered intolerant of habitat loss, requiring large areas of undisturbed forest (Kemp and Boesman 2017b), and is at least hunted locally (del Hoyo et al. 2001). Therefore, the rate of decline in this species is likely greater than the rate of forest loss, and is provisionally suspected to fall in the range 30-49% over three generations. Thus it is proposed that this species be listed as Vulnerable under criteria A3cd+4cd.

 

Great Hornbill (Buceros bicornis) – Current listing NT A2cd+3cd+4cd; C1

  • % forest lost within range 2000-2012 = 6.4%
  • Three-generation period = 55.2 years
  • Extrapolated % decline over three generations = 26.1%

It has been suggested that the main cause of decline in this species is habitat loss (Kemp and Boesman 2017c), although it is also targeted by hunters in several areas throughout its range. Its predictable behaviour in returning to certain feeding sites makes is susceptible to hunting (R. Naniwadekar and A. Datta in litt. 2016), with it being consumed as food and traditional medicine, its casque and feathers used as decorative items in local communities, and it may also be impacted by the pet trade (Eames 2008, Kemp and Boesman 2017b, R. Naniwadekar and A. Datta in litt. 2016). Therefore, the species is suspected to at least warrant being retained under its current listing as Near Threatened, but given the potentially high impact of hunting it is precautionarily proposed that Great Hornbill be uplisted to Vulnerable under criteria A3cd+4cd (30-49% decline over three generations).

 

Bushy-crested Hornbill (Anorrhinus galeritus) – Current listing LC

  • % forest lost within range 2000-2012 = 12.0%
  • Three-generation period = 29.4 years
  • Extrapolated % decline over three generations = 26.9%

This species does appear able to cope with a degree of habitat degradation, though avoids heavily impacted areas (Kemp et al. 2017b). Given the rate of forest loss it appears that the species at least warrants uplisting to Near Threatened, although it is uncertain whether the impact of hunting may mean that its overall rate of decline reaches the threshold for Vulnerable. Therefore, it is suggested that the species be at least uplisted to Near Threatened under criteria A3cd+4cd (declines approaching 30% in three generations), though we request further information as to whether the level of hunting pressure across the range may be sufficient to warrant the species’ listing as Vulnerable under the same criteria (30-49% decline over three generations).

 

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are about these proposed listings. Further information about the species can be found on their BirdLife Datazone pages.

 

References

Beastall, C.; Shepherd, C. R.; Hadiprakarsa, Y.; Martyr, D. 2016. Trade in the Helmeted Hornbill Rhinoplax vigil: the ‘ivory hornbill’. Bird Conservation International 26: 137-146.

del Hoyo, J.; Elliott, A.; Sargatal, J. 2001. Handbook of the birds of the world, Vol 6: Mousebirds to Hornbills. Barcelona, Spain: Lynx Edicions.

Eames, J. C. 2008. Rufous-necked and Great Hornbills confiscated in Myanmar. The Babbler: BirdLife in Indochina: 15.

Kemp, A. C.; Boesman, P. 2017a. Rhinoceros Hornbill (Buceros rhinoceros). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/55909 on 16 October 2017).

Kemp, A. C.; Boesman, P. 2017b. Wreathed Hornbill (Rhyticeros undulatus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/55926 on 16 October 2017).

Kemp, A. C.; Boesman, P. 2017c. Great Hornbill (Buceros bicornis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/55908 on 16 October 2017).

Kemp, A. C.; Boesman, P.; Sharpe, C. J. 2017a. Black Hornbill (Anthracoceros malayanus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/55906 on 16 October 2017).

Kemp, A. C.; Kirwan, G. M.; Sharpe, C. J. 2017. Bushy-crested Hornbill (Anorrhinus galeritus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/55884 on 16 October 2017).

Kinnaird, M. F.; O’Brien, T. G. 2007. The Ecology & Conservation of Asian Hornbills. Farmers of the Forest. The University of Chicago Press, Chicago.

Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; Buchanan, G. M. 2016. Toward quantification of the impact of 21st-century deforestation on the extinction risk of terrestrial vertebrates. Conservation Biology 30: 1070-1079.

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6 Responses to A reassessment of the Red List status of several Asian hornbill species

  1. Praveen J says:

    Great Hornbill:
    I agree with the suggested uplisting of Great Hornbill based on its status in southern India. Though there are still large populations in Periyar & Anamalai subclusters of southern Western Ghats, all of them are undergoing severe pressure in non-protected areas (roughly 50% of its habitat is outside PA network in these clusters) though they are relatively safer inside protected areas.

  2. Ding Li Yong says:

    Wrinkled Hornbill – Not only the bycatch issue is pertinent, this species is also dependent on lowland forest, especially swamp forest, riparian forest and coastal dipterocarp forest, the most threatened of the Sundaic forest assemblages. The species occurs in low densities in logged forests – and have become quite rare in forest remnants in the southern Thai-Malay peninsula – e.g. Panti, Mersing, Arong, Lenggor among others; there are few recent records from Peninsular Thailand. The species merits at least EN – in recognition of these threats.

    • Simon Mahood says:

      Agreed. Wrinkled is a special case. It is very much dependent on low lying level forest, in which it of course needs large trees with holes in which to nest. For habitat reasons it is very rarely seen at regularly visited protected Sundaic lowland forest sites such as Danum and Taman Negara – they are not the right habitat for the species.

      The rate of loss or degradation (logging of large trees) of level lowland forests in the Sundaic region must significantly exceed the loss of general lowland forest formations overall, which given its specific habitat requirements surely makes this species a candidate for EN or CR status.

  3. We are of the view for uplisting for Great Hornbill (Buceros bicornis) from Near Threatened to Vulnerable, not only in view of pressures from hunting, but also due to severe impacts and demands being placed on their habitats. Apart from the issue of hunting in the north-eastern states of India, the serious concern of diversions/approved diversions of many river valleys and forested regions in these parts for developmental projects is a very grave issue today. Large protected habitats in India, does certainly offer a better protection for this species but this is not true in cases where they inhabit areas covered under commercial plantations. We are aware that certain plantation firms in India, have taken a more proactive role in safeguarding the interests of this bird but these are few, and with days to come irregular climatic patterns surely to impact their habitats in the hills, this species is facing threats which are going up.

  4. Anwaruddin Choudhury says:

    I agree upgradation of both Wreathed and Great Pied to Vulnerable. They are losing habitat and also being poached besides losing nesting trees regularly. Their absence in areas where they were plenty even in 1990s in northeastern India is too conspicuous.

  5. Le Manh Hung says:

    Thanks for the good news! I was thinking how and when those species (Great and Wreath Hornbills) will be uplisted. We were also listed those species in the Vietnam Government Degree on the rare and threatened species and is also going to uplisting their status in Vietnam Red Data Book.

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