Narcondam Hornbill (Rhyticeros narcondami): revise global status?

BirdLife species factsheet for Narcondam Hornbill

Restricted to the single, small island of Narcondam, which lies in the Andaman Sea 127 km east of North Andaman Island, this hornbill will always be at the risk of stochastic events. Currently it is assessed as Endangered as the population was believed to be under 250 mature individuals. However, the IUCN SSC Hornbill Specialist Group (https://iucnhornbills.org/) have made considerable efforts to establish the current and recent population size of the species through communication with researchers that have quantified the population on multiple occasions in the past decade.  

The most recent estimate of the population (December 2019 to February 2020) is of 1,026 individuals (95% confidence interval 751 – 1,402) (R. Naniwadekar in litt. to the Hornbill Specialist Group 2020). In addition, Manchi (2017) estimated a population of 1,295 birds from a density extrapolation across the whole island. While the latter may have been too high as the species is predominately found in the lowlands, the densities recorded in these two studies (150 individuals/km2 and 190 individuals/km2) were very similar to the 167 individuals/km2 from fieldwork in April 2010 (Raman et al. 2013), which was not extrapolated to produce a population estimate.

To estimate the number of mature individuals, two pieces of additional information are useful. A previous study investigating the species estimated that the breeding population was 46-53% of the total number of individuals (Vijayan and Sankaran 2000). Second, a male-biased sex-ratio (56/44) was recorded by Manchi (2017), which would slightly reduce the number of mature individuals to consider in the assessment. Using the most recent estimate, and a ratio of mature individuals to all individuals of 50% (a very conservative estimate), the population size is between 375 – 701 mature individuals. Typically we use a ratio of mature individuals to individuals of two-thirds, although the skewed sex ratio would reduce this to 60% in this case. If this ratio is accepted, the revised population estimate is 450 – 841 mature individuals.  

In the light of this newly estimated population size, the species is re-assessed against all Red List Criteria.

Criterion A – Previous population estimates were around 400 individuals (Hussain 1984, 1993), 330- 360 individuals in 1998 (Vijayan and Sankaran 2000), 432- 498 individuals in 2000 (Yahya and Zarri 2002) and 320-340 individuals in 2003 (Vivek and Vijayan 2003). The more recent estimates suggest that there has either been an increase in the total population, or the previous estimates were too low. There is no indication that there has been any decline in the population over the previous three generations (22 years, as the revised generation length for the species is estimated at 7.23 years [Bird et al. 2020]*) from any of the assessments of the population on the island. To the best of our knowledge, there are no threats to cause a rapid decline within the next three generations. Therefore, Narcondam Hornbill is assessed as Least Concern under Criterion A.

Criterion B – The Extent of Occurrence (EOO) from a Minimum Convex Polygon around the breeding/resident range is 7 km2. The estimate of the Area of Occupancy (AOO) actually exceeds this value due to the requirement to calculate the latter value on a 2 km by 2 km grid, but as the latter cannot exceed the former the value of the EOO is substituted for the AOO. The species thus meets the initial threshold for Critically Endangered under Criterion B; however, as the population is stable no other subcriteria are met, and the species is assessed as Least Concern under Criterion B. Threats noted in the past, including introduced goats, hunting and forest clearing have now ceased, including the eradication of the goats and removal of cats (R. Naniwadekar in litt. to the Hornbill Specialist Group 2020).

Criterion C – While the revised population size is below the threshold for listing as threatened under Criterion C, there is no evidence of a continuing decline. Therefore the species qualifies as Least Concern under Criterion C.

Criterion D – The number of mature individuals is now estimated at between 375 – 841, as described above, therefore the species qualifies as Vulnerable under Criterion D1. While the Area of Occupancy is highly restricted, there does not appear to be a plausible threat that could drive the species to Critically Endangered or Extinct within a very short time (typically one generation). Despite close proximity to the epicentre of the 2004 Tsunami the species was unaffected by this event. Consequently, it is not believed that the species qualifies for listing under Criterion D2, despite the highly restricted range.

Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.

It is proposed that Narcondam Hornbill (Rhyticeros narcondami)be listed as Vulnerable under Criterion D1. We welcome any comments on this proposed listing.

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic. By submitting a comment, you confirm that you agree to the Comment Policy.

*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).

An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.

References

Bird, J.P., Martin, R., Akçakaya, H.R., Gilroy, J., Burfield, I.J., Garnett, S., Symes, A., Taylor, J., Şekercioğlu, Ç.H. & Butchart, S.H. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology, online first view.

Hussain, S. A. 1984. Some aspects of the biology and ecology of Narcondam Hornbill (Rhyticeros narcondami). Journal of the Bombay Natural History Society 81: 1–18.

Hussain, S. A. 1993. The biology and ecology of the Narcondam Hornbill. Hornbill 4: 27–29.

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. Gland, Switzerland and Cambridge, UK: IUCN. Available at www.iucnredlist.org/technical-documents/categories-and-criteria

Manchi S. S. 2017. Status, Ecology and Conservation of Narcondam hornbill Aceros narcondami on Narcondam island, India (Report No. 189). Salim Ali Centre for Ornithology and Natural History project/Technical consultancy reports. Retrieved from the Salim Ali Centre for Ornithology and Natural History website: http://www.sacon.in/publications/reports/

Raman, T. R. S., Mudappa, D., Khan, T., Mistry, U., Saxena, A., Varma, K., Ekka, N., Lenin, J., and Whitaker, R. 2013. An expedition to Narcondam: observations of marine and terrestrial fauna including the island-endemic hornbill. Current Science 105(3): 346-350.

Vijayan, L. and Sankaran, R. 2000. A study on the ecology, status and conservation perspectives of certain rare endemic avifauna of the Andaman and Nicobar Islands. Final Report, Sálim Ali Centre for Ornithology and Natural History, Coimbatore.

Vivek, R. and Vijayan, V. S. 2003. Ecology and conservation of the Narcondam Hornbill (Aceros narcondami) at Narcondam Island Sanctuary, India. Interim Report, Sálim Ali Centre for Ornithology and Natural History, Coimbatore.

Yahya, H. S. A.; Zarri, A. A. 2002. Status, ecology and behaviour of Narcondam hornbill (Aceros narcondami) in Narcondam Island, Andaman and Nicobar Islands, India. Journal of the Bombay Natural History Society 99: 434-445.

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5 Responses to Narcondam Hornbill (Rhyticeros narcondami): revise global status?

  1. James Eaton says:

    This hornbill has already had one campaign to protect its habitat (see https://www.conservationindia.org/campaigns/narcondam).

    Downlisting the threat status of the species could potentially have a negative effect further down the line, especially given the recent onslaught on protected areas by the current administration. (https://www.conservationindia.org/campaigns/save-the-destruction-of-dibang-valley and https://www.thehindu.com/news/national/other-states/nbwl-nod-for-coal-mining-in-assam-elephant-reserve/article31427115.ece)

    James

  2. Dr Anwaruddin Choudhury says:

    I do not see any valid reason for its down listing. It is a species which is confined to a single site in its entire range, that too a very small island. There could be various issues – disease, loss of nesting trees due to natural calamity like tsunami and so on. Even inbreeding could be an issue in future. Hence, it must continue to be in Endangered category.

  3. Criterion D has been used to downlist the status of the Narcondam Hornbill from Endangered to Vulnerable. One of the arguments is that there are not any plausible threats that could drive the species to higher risk categories. However, there may be reason(s) (particularly point 2) that can cause drastic declines in this single population and that may need to be considered as a cautionary principle.
    1) Cats have not been removed from the island. I have been wrongly cited on the forum in this regard. There are at least two cats on the island. We have noticed hornbills foraging on the ground on multiple occasions. The possibility of cats potentially preying on hornbills cannot be ruled out. We have documented the cat preying on a pond heron on the island. The cats have been photographed moving far into the interior of the island and we have camera trapped it at 400 m asl halfway up the mountain and several km away from the barracks. Cats probably may not cause drastic declines in species abundances as long as their numbers do not go up.
    2) There are reports of chickens being occasionally taken on the island. There is a potential threat to the hornbills of disease transmission. Given that it is a small island and a single population, disease transmission can have drastic impacts on the population. This may need to be considered. Susceptibility to diseases in the hornbills needs to be studied in the future.

  4. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you once again,
    BirdLife Red List Team

  5. Red List Team (BirdLife International) says:

    Preliminary proposal

    In the absence of a known continued decline, based on our current knowledge of a population size estimated to be 375-841 mature individuals, and a low Area of Occupancy (AOO) of c. 7 sqkm, our preliminary proposal for the 2020 Red List would be to retain the Narcondam Hornbill as Vulnerable under Criterion D1+2.

    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021 (information on the IUCN Red List update process can be found here), following further checking of information relevant to the assessments by both BirdLife and IUCN.

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