BirdLife International factsheet for Henst’s Goshawk
Henst’s Goshawk is endemic to Madagascar, and inhabits primary rainforest to the east, and dry rainforest to the west of the island (Kemp et al., 2020). The most optimistic, recent population estimate stands at 1,000-2,250 individuals (R. Thorstrom in litt., 2016), and the population is suspected to be in decline due to ongoing deforestation.
The species has been considered Near Threatened, approaching a globally threatened status under Criterion C1+2a(i); D1 (BirdLife International, 2020). However, this is no longer tenable due to the reconsideration of its population size, which may warrant a change in Red List Category. We have therefore reviewed this species here against all the criteria.
Criterion A: The population trend for this species has never been properly quantified, but it is suspected to be declining through ongoing habitat loss due to deforestation. IUCN guidelines stipulate that rates of decline should be measured over the longer of 10 years or 3 generations (IUCN Standards and Petitions Committee, 2019). The generation length for Henst’s Goshawk has been recalculated to 7.9 years (Bird et al., 2020)*. Therefore, the rates of reduction for this species are calculated over 23.7 years.
An analysis of deforestation between 2000 and 2012 (Tracewski et al. 2016) estimated a rate of forest loss of 10% over 3 generations for this species. Assuming that the population declines at the same rate as forest loss, this does not meet the threshold for classification as Vulnerable (population size reduction ≥ 30% over 3 generations). Henst’s Goshawk can therefore be classed as Least Concern under this criterion.
Criterion B: The Extent of Occurrence (EOO) for Henst’s Goshawk is believed to be 673,000 km² (BirdLife International, 2020), which is far above the threshold for Vulnerable (EOO < 20,000 km²). Thus, Henst’s Goshawk is classed as Least Concern under criterion B1. The Area of Occupancy (AOO) has not been quantified for this species, so it cannot be assessed under criterion B2.
Criterion C: The most recent population estimate for Henst’s Goshawk is 1,000-2,250 individuals, although the upper limit may actually be 2,000 individuals (R. Thorstrom in litt., 2016), equating to roughly 670-1,500 mature individuals. This meets the requirements for classification under criterion C, subject to the conditions of other sub-criteria being met. The rate of decline here is only suspected, which precludes listing as threatened under criterion C1. However, the suspected rate of decline is approaching a rate of 10% over three generations, and as such this species may be considered Near Threatened under criterion C1.This species has an inferred continuing decline, as required for classification under C2. Classification under C2 also requires the fulfilment of other sub-criteria. The number of mature individuals is not believed to fluctuate. The subpopulation structure is not fully understood. However, with an estimated population of 670-1,500 mature individuals, it is conceivable that there may be <1,000 mature individuals in the largest subpopulation. Additionally, if this species was found to exist in only one subpopulation, this would meet the threshold for classification as Vulnerable here. We therefore seek information regarding the subpopulation size and structure for Henst’s Goshawk. Under current information, Henst’s Goshawk may be considered Near Threatened, approaching a listing as threatened under criterion C2a(i).
Criterion D: There is an estimated 670-1,500 mature individuals for this species (R. Thorstrom in litt. 2016). Assuming that the true population size is towards the lower end of this estimate, it meets the threshold for Vulnerable (number of mature individuals <1,000). Henst’s Goshawk may therefore be classified as Vulnerable under criterion D1.
Criterion E: To the best of our knowledge, no quantitative analysis has been performed for this species, so it cannot be assessed against this criterion.
Therefore, it is proposed that Henst’s Goshawk (Accipiter henstii) be listed as Vulnerable under criterion D1. We welcome any comments to the 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 the species’ Red List status. Therefore, please make sure your comments are relevant to the species’ Red List status and the information requested. 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.
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.
BirdLife International (2020) Species factsheet: Accipiter henstii. Downloaded from http://www.BirdLife.org on 25/03/2020.
IUCN Standards and Petitions Committee, 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.
Kemp, A.C., Christie, D.A. & Kirwan, G.M. (2020). Henst’s Goshawk (Accipiter henstii). 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/53088 on 25 March 2020).
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.