Secretarybird (Sagittarius serpentarius): Revise global status?

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in 1973 and 2004 have failed to find Secretarybirds in northern Cameroon (Thiollay, 2001; Buij et al., 2013; R. Buij, unpublished data).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km) and a 100% reduction in the observation rate in National Parks (from 2.3 to 0 birds/100 km; Thiollay, 2006; R. Buij unpublished data in Ogada et al., in prep.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.

References

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

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8 Responses to Secretarybird (Sagittarius serpentarius): Revise global status?

  1. Secretarybirds are certainly facing rapid declines due to numerous threats over and above the impacts of habitat loss. BirdLife South Africa has fitted trackers to 14 juvenile Secretarybirds since 2012 and we currently sit with a fatality rate of 46% for birds under the age of three years (Whitecross et al. unpublished). This eliminates approximately half of the recruiting population prior to them entering the breeding population. While a conservation status of Critically Endangered would certainly go a long way to assisting the conservation of these embattled raptors I think at the very least they deserve to be uplisted to Endangered in the immediate review.
    We are working on fine-scale habitat selectivity to attempt to quantify just how much available habitat remains for these birds in South Africa, but this analysis is still in its infancy and will likely only be available next year. We hope to collaborate with colleagues across the continent to upscale this analysis and quantify the available habitat for the entire distribution.

  2. Our research team conducted >10,800km of raptor roadcounts throughout the extent of Ethiopia from 2010 – 2017 and, of 22,909 individual raptors recorded, we recorded only 1 Secretarybird (0.004% of raptors observed; 0.000092 individuals/km). While these surveys were not specifically designed to sample Secretarybird, and survey routes occurred across a range of suitable and unsuitable habitat for the species, I believe this evidence, coupled with the large and growing human population size, loss of habitat, and limited protection even within flagship national parks in the country, to be indicative of a small and highly endangered population of the species in Ethiopia.

    Evan R. Buechley, PhD
    International Programs Director
    HawkWatch International

  3. Our research team conducted >10,800km of raptor roadcounts throughout the extent of Ethiopia from 2010 – 2017 and, of 22,909 individual raptors recorded, we recorded only 1 Secretarybird (0.004% of raptors observed; 0.000092 individuals/km; NOTE: we have a few additional incidental observations In Awash, Ali Deghe, and Yangudi Rassa National Parks). While these surveys were not specifically designed to sample Secretarybird, and survey routes occurred across a range of suitable and unsuitable habitat for the species, I believe this evidence, coupled with the large and growing human population size, loss of habitat, and limited protection even within flagship national parks in the country, to be indicative of a small and highly endangered population of the species in Ethiopia.

    Evan R. Buechley, PhD
    International Program Director
    HawkWatch International

  4. Phil Shaw says:

    A provisional analysis of Southern African Bird Atlas Project data for Secretarybird shows that reporting rates for this species in South Africa declined between SABAP1 (1987–1992) and SABAP2 (2007–2020). Over this 24 year period, reporting rates dropped by 70%; equivalent to an annual decline rate of 4.9%. This equates to a 75% decline when projected over three generation lengths (27.9 years); slightly lower than the decline reported by Hofmeyr et al. (2014) for South Africa, and the composite figure obtained from road transect surveys in Kenya and Botswana.

    Phil Shaw, Arjun Amar, Darcy Ogada

  5. 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

  6. Red List Team (BirdLife International) says:

    Preliminary proposal

    While it is clear that some national declines appear to reach or exceed 80% over three generations, there remain many countries for which we have no data, and more information on the drivers of such a widespread decline is required. The road surveys compared in Garbett et al., (2018) are not identical in length; total kilometres driven were less in the more recent surveys, potentially influencing the observation rates. Additionally, revision of the South Africa SABAP data has shown that the decline in reporting rates there over a length of three generations has not been as bad as initially reported by Hofmeyr et al., (2014). Furthermore, reported sightings on eBird do not show this species disappearing from large areas, as would be expected from a species experiencing large continent-wide declines. The suspected rates of decline for this species is therefore placed in the 70-80% band.

    As such, our preliminary proposal for the 2020 Red List would be to list Secretarybird as Endangered under Criterion A2acde+3cde+4acde.

    We urge more research and monitoring in less reported parts of its range, and if further evidence arises supporting high rates of decline, Secretarybird may be uplisted in future to a higher threat category.

    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, following further checking of information relevant to the assessments by both BirdLife and IUCN. The final publication date will be publicised by IUCN here: https://www.iucnredlist.org/assessment/updates

  7. Bernard Amakobe says:

    Over a 9-year period (2011 – 2020, within the Tsavo Conservancy Area Conservancies and Ranches, very few successful breeding attempts have succeeded, and the bird density has remained the same. In fact, some roosting sites have not been visited for extended periods indicating either being abandoned or no new recruits. The unprotected areas are almost virtually avoided by Secretarybird as evidenced through transects, foot patrols and Ad Lib observations.
    On a two-year Zoological Society of London (ZSL-Funded) project I noted the Secretarybird migrates locally depending on the season. During the breeding season which is mainly when we have either short or long rains here in South-East Kenya, they are mostly in pairs and do not move away from their preferred roosting site which also acts as the breeding site. Most of these habitats are being converted to other land use type especially for commercial purposes like the SGR and the proposed Super Expressway meaning the species is being pushed slowly to extinction.
    Breeding pairs are very keen on choosing when to attempt breeding as I noted there were many “false attempts” at breeding due to the long drought and unfavorable weather conditions. This means even with an optimal habitat like what we have in the protected areas, adverse weather changes which we are seeing affect breeding success intensely. As such, I support the listing of Secretarybird as Endangered under Criterion A2acde+3cde+4acde.

  8. In Tanzania we are still finding birds outside PAs but not many. They appear to still be doing OK within the larger savanna PAs which continue to provide a source population.
    No surveys / transects that I am aware of.

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