BirdLife International factsheet for the Secretarybird.
The Secretarybird is a large raptor that occurs across a large range in Africa. The range stretches from sub-saharan Mauritania in the west to Ethiopia in the east, and down to South Africa in the south. It inhabits open landscapes, including open plains and grasslands (Baker et al., 2011), and the population size is estimated to range between 6,700-67,000 mature individuals (BirdLife International, 2020).
This species is threatened by widespread habitat loss from agricultural development, encroachment of woody vegetation, and impacts of urbanisation (Baker et al., 2011; Whitecross et al., 2019; Colyn et al., in review 2020). As such, the Secretarybird is suspected to have undergone rapid declines, and is currently considered Vulnerable under Criterion A4acd (BirdLife International, 2020).
However, new information regarding the rate of declines suggest that the species may warrant a change in Red List status. Therefore, we have fully reviewed the species here against all criteria.
Criterion A: The Secretarybird is believed to be experiencing rapid declines, but fully quantifying this is difficult. The rate of decline is measured over the longer of 10 years or three generation lengths. The generation length for the Secretarybird has been recalculated to 9.3 years (Bird et al., 2020)*. Rates of decline for this species should therefore be assessed over a length of 27.9 years.
A 73.5% reduction in observations was reported in South Africa between 1991 and 2010 (Hofmeyr et al. 2014), equating to an inferred decline of 86% over three generations. Additionally, a 78% decline in Secretarybirds has been recorded in protected and unprotected areas in Botswana between 1993 and 2015 (Garbett et al., 2018), equating to a decline of 86% in three generations. There are further reports of large declines in Eswatini (Monadiem et al., 2003). Repeated surveys in 1973 and 2004 have failed to find Secretarybirds in northern Cameroon (Thiollay, 2001; Buij et al., 2013; R. Buij, unpublished data). A comparison of roadside counts that took place in 1969-1973 and in 2003-2004 across West Africa (Mali, Burkina Faso and Niger) detected a 100% reduction in the observation rate in unprotected areas (from 1.5 to 0 birds/100 km) and a 100% reduction in the observation rate in National Parks (from 2.3 to 0 birds/100 km; Thiollay, 2006; R. Buij unpublished data in Ogada et al., in prep. a). Scaled across three generations, these rates of reduction equate to a 99% reduction in unprotected areas and a 99% reduction in National Parks in the Sahel region. In Kenya, encounter rates in protected areas declined by 15% between 1972 and 2012 (from 1.32 to 1.12 birds/100 km) and by 96% in unprotected areas over the same period (from 5.91 to 0.24 birds/km). These reductions equate to a decline of 11% in protected areas and 89% in unprotected areas over three generations (Ogada et al., in prep. b).
New research being conducted by Ogada et al., (in prep. a) into the rates of decline for Secretarybird based on the above mentioned declines in protected and unprotected areas in Kenya and Botswana takes into account the size of the range within each country. For Kenya, they report a total reduction of 86% over three generation in protected and unprotected areas combined (Ogada et al., in prep. a). Overall declines in Botswana are based on data from Garbett et al., (2018), who report declines of 86% over three generations in protected and unprotected areas combined (Ogada et al., in prep. a). The change in encounter rates was then weighted by the species’s range within each country. The size of the species’s range in Botswana and Kenya is roughly equal, with the range in Botswana being 1.3 times the size of the range in Kenya; hence the rate of reduction observed in Botswana was weighted by a factor of 1.3 (Ogada et al., in prep. a). This resulted in a weighted mean rate of population change of 86% over three generations in Kenya and Botswana combined (Ogada et al., in prep. a).
The Secretarybird appears to be observed more frequently in South Africa, Botswana and Kenya than other parts of its range (Kemp et al., 2020). Assuming that frequency of observations is directly proportional to population size, this suggests that the populations here represent key numbers of the Secretarybird’s remaining global population. Observational data suggests declines of 86% of the population in South Africa (see Hofmeyr et al., 2014). Equally, the populations in Botswana and Kenya are declining by 86% over three generations (Ogada et al., in prep. a). Similar high rates of decline have been reported from other parts of its large range, suggesting that the rate of decline is extensive. Data for the known populations suggests an overall decline rate of 80-90% in three generations, which would qualify the species as Critically Endangered. While we do not currently have data from all countries in this species’s range, the data we do have seems to represent a large proportion of the population. Assuming that habitat loss and the impacts of urbanisation exist to the same degree throughout its range, the rest of the population may also be experiencing similar levels of decline. The drivers of decline, particularly those relating to urban expansion, are likely to continue into the near future. Whether they are likely to continue at the same rate over the next three generations (28 years) however, is not clear, as Secretarybird is receiving some conservation attention in some parts of its range. In spite of this, if the above assumptions are true, then the Secretarybird may be considered Critically Endangered under Criterion A2abc.
Criterion B: The Secretarybird has an EOO of 23,200,000 km² (BirdLife International, 2020), which is far too big for the species to be considered threatened under Criterion B1. This species may therefore be considered Least Concern under this criterion.
Criterion C: The population size of the Secretarybird was estimated in 2001 to range between 6,700-67,000 mature individuals (BirdLife International, 2020). Since then, the species has been undergoing a decline at the estimated rate of 80-90% in three generations. This would mean that the population size has roughly declined by at least 67% since 2001, placing the population size estimate now between 2,200-22,200 mature individuals. Given the size of its range, it is more likely that the true population size falls in the mid to upper end of that estimate, which may mean it triggers the initial threshold of <10,000 mature individuals for classification as threatened under Criterion C.
However, in order to fully classify as such here, other sub-criteria must be met. The rate of decline for Secretarybird is estimated to be greater than 25% in one generation, which meets the requirements of sub-criterion 1. The estimated continuing decline also meets the requirements for part of sub-criterion 2; however the species is not believed to experience extreme fluctuations in the number of mature individuals, so condition b is not met. Given its large range, it is unlikely that 100% of mature individuals occur in one subpopulation, so condition a(ii) is not met. The rest of the subpopulation structure is unclear. Depending on the true population size, it is possible that there are <1,000 mature individuals in each subpopulation. Given the uncertainty around this and the true population size, Secretarybird does not fully qualify for listing as threatened under this criterion. However, it may tentatively be considered Near Threatened, approaching a listing as threatened under Criterion C1.
Criterion D: The revised population size estimate is 2,200-22,200 mature individuals. Even if the true population size is at the lower end of the estimate, it currently remains too high to be considered threatened under Criterion D. The Secretarybird may therefore be listed as Least Concern under this criterion.
Criterion E: To the best of our knowledge, no quantitative analysis of the probability of extinction has been conducted on this species so the Secretarybird cannot be assessed under this criterion.
We therefore suggest that Secretarybird (Sagittarius serpentarius) be listed as Critically Endangered underCriterion A2abc. 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.
Baker, N., Brouwer, J., Baker, L., Sinclair, T., Harebottle, D., Buij, R. 2011. The status of the Secretarybird Sagittarius serpentarius with special reference to Tanzania and declines across the continent. A preliminary report to the UK CITES Scientific Authority (Fauna).
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: Sagittarius serpentarius. Downloaded from http://www.BirdLife.org on 09/04/2020.
Buij, R., Croes, B.M., Gort, G., and Komdeur, J., 2013, The role of breeding range, diet, mobility and body size in associations of raptor communities and land-use in a West African savannah, Biological Conservation, 166, pp: 231-246
Colyn, R.B., Lee, A., Smit-Robinson, H., Ryan, P. 2020. The use of remote sensing and in-situ data collection to assess habitat state and rate of change within the mesic highland grasslands of South Africa, Lesotho and Eswatini.In review.
Garbett R; Herremans M; Maude G; Reading RP; Amar A. 2018. Raptor population trends in northern Botswana: a re-survey of road transects after 20 years. Biological Conservation 224: 87–99.
Hofmeyr, S. D.; Symes, C. T.; Underhill, L. G. 2014. Secretarybird Sagittarius serpentarius population trends and ecology: insights from South African citizen science data. PLoS ONE 9: e96772.
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., G. M. Kirwan, D. A. Christie, and J. S. Marks (2020). Secretarybird (Sagittarius serpentarius), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.secret2.01
Monadijem, A., Boycott, RC., Parker, V., and Culverwell, J., 2003, Threatened vertebrates of Swaziland, Swaziland Red Data Book: Fishes, amphibians, reptiles, birds and mammals, pp. 66-72
Ogada, D., Shaw, P., Buij, R., Thiollay, J.M., Garbett, R., Herremans, M., Virani, M.Z., Amar, A., Maude, G., Dunn, A., and Thomsett, S., in prep. a Continental declines of Africa’s raptors.
Ogada, D., Shaw, P., Virani, M.Z., Thiollay, J.M., Kendall, C.J., Odino, M., Patel, T., Wairasho, P., Dunn, L., Thomsett, S., in prep. b. Raptor declines in Kenya over the past 45 years.
The Cornell Lab for Ornithology, 2020, Range Map for Secretarybird Sagittarius serpentarius, available at https://ebird.org/species/secret2, accessed 30/04/20.
Thiollay, J.M. (2001). Long-term changes of raptor populations in northern Cameroon. J. Raptor Res. 35: 173-186
Thiollay, J.M., 2006, The decline of raptors in West Africa: long-term assessment and the role of protected areas, Ibis, 148, pp. 240-254
Whitecross MA; Retief EF; Smit-Robinson HA. 2019. Dispersal dynamics of juvenile Secretarybirds Sagittarius serpentarius in southern Africa, Ostrich 90(2): 97-110