Archived 2020 topic: Tickell’s Brown Hornbill (Anorrhinus tickelli): request for information

This discussion was first published as part of the 2018 Red List update. At the time a decision regarding its status was pended, but to enable potential reassessment of this species as part of the 2020 Red List update this post remains open and the date of posting has been updated.

Tickell’s Brown Hornbill (Anorrhinus tickelli) is predominantly found in dense forest of southern Myanmar and adjacent Thailand up to 1,500m (Kemp and Boesman 2017). As with many hornbill species in this region deforestation and hunting may be leading to population declines (see Kinnaird and O’Brien 2007; see also this additional topic), and the species is currently assessed as Near Threatened as a result of these threats (BirdLife International 2017).

The species’ population size has been suggested to be potentially small, yet there remains no current estimate. It had been considered to be more common on the Thai side of its range, but a recent paper by Trisurat et al. (2013) has suggested that the species may now be highly range-restricted in Thailand, and so the population size there may in fact be quite small. Therefore, given this information and using the new information regarding forest loss from Tracewski et al. (2016) (see here for further info), this species will be re-assessed against all criteria.

 

Criterion A – Tracewski et al. (2016) measured the forest loss within this species’ range between 2000 and 2012 as c.2,790km2. This roughly equates to a rate of forest loss of 8.4% over 3 generations (33.3 years) for this species, with the assumption that population changes may be proportional to forest change. Therefore, unless hunting may be considered to account for >15% declines over 3 generations, this species is unlikely to approach the threshold for Vulnerable under criterion A.

Criterion B – The Extent of Occurrence (EOO) of this species, calculated using a Minimum Convex Polygon (see IUCN 2001, 2012, Joppa et al. 2016) is 212,000km2. This far exceeds the threshold for Vulnerable under criterion B1.

Trisurat et al. (2013) estimated the extent of suitable habitat for this species in Thailand to be 1,864km2. While Trisurat et al. referred to this as an extent of occurrence, this actually would at best represent a maximum Area of Occupancy (AOO) value instead, because it does not meet the IUCN guidelines for classification as an EOO (see IUCN Standards and Petitions Subcommittee 2017). Tracewski et al. (2016) measured the amount of available forest (as a proxy for the Area of Occupancy) across the species’ whole range as c.86,450km2. It should be stressed that this is a maximum potential AOO, especially given the value of Trisurat et al. (2013), and so the species’ AOO is likely less than the value of Tracewski et al. (2016). However, given that the range value of Trisurat et al. for Thailand alone is so close the global threshold for Vulnerable under criterion B2 (2,000km2) it is very unlikely that the global AOO value would remain beneath this threshold. Therefore, the species likely does not warrant listing under this criterion.

Criterion C – Taking population density estimates for A. tickelli and closely related species, and assuming only a proportion of its range (using the max AOO value of Tracewski et al. [2016]) is occupied would give a population size of c. 23,000 mature individuals. However, this could still be far too large a population size estimate given the information from Trisurat et al. (2013). Using their max AOO value instead would give a population size of c.3,700 mature individuals in Thailand, and while the species’ AOO in Myanmar has not been measured, based on this figure the appropriate population size range is likely 2,500-9,999 mature individuals.

To qualify as Vulnerable, the species would still need to meet certain conditions. The species would not qualify as Vulnerable under criterion C1 because the rate of decline of this species is uncertain (a high level of confidence is required for this criterion). Also the population is likely fragmented, occurring in multiple sub-populations and is not known to undergo extreme fluctuations. Therefore, it would not qualify for Vulnerable under criteria C2a(ii) and C2b.

This leaves criterion C2a(i). To be listed as Vulnerable under this criterion would require the largest sub-population to contain ≤1,000 mature individuals, and given the already high level of uncertainty regarding population estimates it is uncertain whether any sub-population is this small. Therefore, information is urgently sought regarding both the overall population size, and sub-population sizes to see whether this species warrants listing as Vulnerable under this criterion.

Criterion D – Even though the population size is difficult to estimate clearly, it is still suspected to be >1,000 mature individuals, and the species is not limited to a very small number of ‘locations’ (see IUCN Standards and Petitions Subcommittee 2017 for IUCN definition of a ‘location’) or very small AOO. Therefore, it does not warrant listing under this criterion.

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

 

Therefore, it appears that the only criterion where the species may now approach or meet the threshold for Vulnerable is C2a(i). To better assess this species against this criterion, we therefore urgently request any information regarding the global population size, and sub-population sizes.

 

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 relevant to the information that is sought, or about the species’ Red List status.

 

References

BirdLife International. 2017. Species factsheet: Anorrhinus tickelli. Downloaded from http://www.birdlife.org on 14/11/2017.

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. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. Available at: www.iucnredlist.org/technical-documents/categories-and-criteria.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Joppa, L. N.; Butchart, S. H. M.; Hoffmann, M.; Bachman, S. P.; Akçakaya, H. R.; Moat, J. F.; Böhm, M.; Holland, R. A.; Newton, A.; Polidoro, B.; Hughes, A. 2016. Impact of alternative metrics on estimates of extent of occurrence for extinction risk assessment. Conservation Biology 30: 362-370.

Kemp, A. C.; Boesman, P. 2017. Tickell’s Brown Hornbill (Anorrhinus tickelli). 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 https://www.hbw.com/node/55883 on 14 November 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.

Trisurat, Y.; Chimchome, V.; Pattanavibool, A.; Jinamoy, S.; Thongaree, S.; Kanchanasakha, B.; Simcharoen, S.; Sribuarod, K.; Mahannop, N.; Poonswad, P. 2013. An assessment of the distribution and conservation status of hornbill species in Thailand. Oryx 47(3): 441-450.

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9 Responses to Archived 2020 topic: Tickell’s Brown Hornbill (Anorrhinus tickelli): request for information

  1. Rob Martin (BirdLife International) says:

    Preliminary proposals

    Based on available information, our proposal for the 2018 Red List would be to pend the decision on this species and keep this discussion open until 2019, while leaving the current Red List category unchanged in the 2018 update.

    Final 2018 Red List categories will be published on the BirdLife and IUCN websites in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  2. Ricardo Cavalieri says:

    It’s been categorized as Vulnerable (with the A. austeni) by Siam. Besides, the A. austeni is also threatened in Indochina.

  3. Rob Martin (BirdLife International) says:

    Based on available information, our proposal for the 2019 Red List would be to pend the decision on this species and keep the discussion open until 2020, while leaving the current Red List category unchanged in the 2019 update.

    Final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  4. Red List Team (BirdLife International) says:

    The rate of decline under Criterion A is measured over the longer of 10 years or three generation lengths of the species. The generation length for Tickell’s Brown Hornbill has recently been recalculated to 5.8 years (Bird et al. 2020), meaning that trends should be assessed over 17.4 years (three generations) under Criterion A.

    Global Forest Change data on tree cover loss up to 2019 have now been released and made available via Global Forest Watch. Based on these data, over three generations (17.4 years) approximately 8.8% of tree cover with >30% canopy cover was lost from within the species’s range (Global Forest Watch 2020). This does not change the above assessment under Criterion A.

    References:
    Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.
    Global Forest Watch. 2020. Interactive Forest Change Mapping Tool. http://www.globalforestwatch.org

  5. Lay Win says:

    We just have some records for this species (Tickell’s BH) as we didn’t do the survey on this species in detail. So, it is a little bit difficult to estimate the population size (anyway, I would say the population is less than 500 individuals in Myanmar). But we can say that the population is decreasing by looking at the forest destruction.
    Here is the information of this species we recorded;
    19 individuals in 2014 in Ngawun Reserve Forest,
    8 individuals in 2016 in Ngawun Reserve Forest and
    33 individuals in 2019 (5 in Lenya Reserve Forest, 26 in Ngawun Reserve Forest, 2 in Htaungpru Reserve Forest). We were focused only on Hornbill species in five different sites, 82 km in total of line transects (18 km in Lenya RF, 48 km in Ngawun RF, 5 km in Parkchan RF and 11 km in Htaungpru RF) and we walked twice a day at a speed of 1 km/h morning and evening.
    Illegal logging, hunting, agriculture encroachment and road construction through the reserve forest are increasing. But Hornbills are not targeted species for hunters. I noticed that the agriculture encroachment is keep going at the same time when the road construction is increasing. Along with the roads and encroachment of settlements into the forest comes the hunting pressure.

  6. 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

  7. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information and suspecting ongoing declines due to habitat loss, our preliminary proposal for the 2020 Red List would be to list the Tickell’s Brown Hornbill as Near Threatened, nearly meeting Criterion C2a(i).

    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.

  8. Red List Team (BirdLife International) says:

    We are grateful to the Hornbill Specialist Group for the following extra information and their efforts in trying to improve the understanding of this species’s status.

    Nesting data has been provided by Dr. Vijak Chimchome of the Thailand Hornbill Project, Hornbill Research Foundation, Kasetsart University.
    In 29 years of nest monitoring in Huai Kha Khaeng NP from 1991 to 2020, the Thailand hornbill project monitored 44 nests of the species and estimated that 165 chicks were produced with around 5.6 chicks produced per year. The total number of nesting attempts (nests sealed) in these years was only 120. Out of the 120 nesting attempts, 73 were successful (60.8% nesting success).

    As there is no current data on abundance/density estimates available and the most reliable one from Thailand is from the 2013 paper, we can only speculate that there may have been a decline in its suitable habitat (based on other forest cover change data) and with existing threats continuing, there may be a decline in the population. The nesting data from one park which is probably the best single location for the species suggests low nesting attempts and success and recruitment with the long-term nest monitoring data. If we assume a density of 2 to 5 birds per sqkm across its range (assuming Kinnaird & O’Brien’s suitable habitat estimate of 1710 km2 which is likely to have actually declined since that estimate) – the population estimate falls within a range of 3400-8500 birds. However, these numbers are highly speculative and guesswork in the absence of reliable current data.

  9. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Tickell’s Brown Hornbill is recommended to be listed as Near Threatened, approaching the threshold for listing as threatened under Criterion C2a(i).

    Many thanks for everyone who contributed to the 2020 GTB Forum process. The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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