Archived 2020 topic: Wallace’s Hawk-eagle (Nisaetus nanus): revise global status?

BirdLife species factsheet for Wallace’s Hawk-eagle

Wallace’s Hawk-eagle (Nisaetus nanus) occurs from southern Myanmar through peninsular Thailand and Malaysia to the islands of Borneo and Sumatra. It is found in evergreen forests in the lowlands and occasionally on lower hill-slopes up to 1,000 m. Even though Wallace’s Hawk-eagle is widespread, it is uncommon to rare throughout its range.

The species is increasingly threatened by the loss, degradation and fragmentation of lowland rainforest. Even within protected areas, forests are cleared for conversion into palm oil and rubber plantations, as well as into agricultural land. Over 15 million ha of forest were logged on Sumatra and Borneo between 1985 and 1997, while forest fires are becoming increasingly frequent and severe (Clark and Kirwan 2018). In Thailand, Wallace’s Hawk-eagle is presumed close to extinction, as essentially all lowland forest has been cleared by now (Clark and Kirwan 2018). 

At least locally, the species was found to tolerate a low level of habitat degradation. In Kalimantan, Sumatra and Malaysia, it was recorded in logged forests and occasionally even within oil palm plantations (Yeap Chin Aik in litt. 2007, 2008). However, a study in Malaysia recorded it in primary forest prior to selective logging, but not subsequently. Overall, the species always keeps in close proximity to patches of continuous, mature forest (Wells 1999). Generally, it is found more readily in undisturbed forest remnants.

Wallace’s Hawk-eagle is currently listed as Vulnerable on the IUCN Red List. However, using new information regarding the rate of forest loss from Tracewski et al. (2016), this species appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

Criterion A – Tracewski et al. (2016) measured the forest loss within this species’s range between 2000 and 2012 as c. 81,400 km2. This roughly equates to a rate of forest loss of 27.8% over 3 generations (22.7 years; Bird et al. 2020*) for this species, with the assumption that habitat loss has continued at the same rate to the present day. While some populations have shown resilience to habitat modification, others have been found absent from disturbed forests. Thus, it may be precautionarily assumed that population changes are proportional to forest cover change. Consequently, Wallace’s Hawk-eagle does not appear to meet, but to approach the threshold for listing as threatened under Criterion A, and as such may be listed as Near Threatened under Criterion A2c.

Criterion B – This species has a very large range (Extent of Occurrence = 3,580,000km2) and  therefore does not approach the thresholds for listing as Vulnerable under Criterion B1. The species therefore qualifies as Least Concern under this criterion.

Criterion C – The population size of Wallace’s Hawk-eagle is preliminarily estimated to fall in the band 2,500-9,999 mature individuals. This may warrant the species listing as Vulnerable under Criterion C, given the species is considered to be declining, as long as other conditions are met. A listing under Criterion C1 would require Wallace’s Hawk-eagle to be undergoing an observed, estimated or projected decline of at least 10 % over three generations. As the suspected rate of decline for this species was inferred based on estimates for forest loss, it cannot be assessed against Criterion C1.

Given the large range of the species, Wallace’s Hawk-eagle can be considered in more than one subpopulation, with the largest of them likely yielding more than 1,000 mature individuals. The population size is not known to fluctuate. Therefore, Wallace’s Hawk-eagle does not fall below the threshold for a listing under Criterion C2. Overall therefore, the species may be considered Least Concern under Criterion C.

Criterion D – The population size of this species is estimated at 2,500-9,999 mature individuals and is therefore too large to fall below the threshold (<1,000 mature individuals) for listing this species as Vulnerable under Criterion D1. The species therefore qualifies as Least Concern.

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.

Therefore, it is proposed that Wallace’s Hawk-eagle (Nisaetus nanus)be listed as Near Threatened, approaching the threshold for listing as threatened under Criterion A2c. 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.; 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.

Clark, W.S.; Kirwan, G.M. 2018. Wallace’s Hawk-eagle (Nisaetus nanus). 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, Spain. (retrieved from https://www.hbw.com/node/53181 on 11 September 2018).

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.

Wells, D. 1999. The Birds of the Thai-Malay Peninsula, vol. 1: Non-passerines. Academic Press, London, UK.

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2 Responses to Archived 2020 topic: Wallace’s Hawk-eagle (Nisaetus nanus): revise global status?

  1. Red List Team (BirdLife International) says:

    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 (22.7 years) approximately 35.1% of tree cover with >30% canopy cover was lost from within the species’s range (Global Forest Watch 2020). This meets the threshold for listing as Vulnerable under Criterion A2c.

  2. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    New data on forest loss, which were recently released via Global Forest Watch, indicate that this species’s habitat is declining at a rate of <30% over three generations. This does not represent a change to the current Red List status. Wallace's Hawk-eagle thus continues to qualify for listing as Vulnerable under Criterion A2c+3c+4c.

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