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GENETIC MANAGEMENT GUIDELINES

Black Rhinoceros Diceros bicornis

The black rhinoceros Diceros bicornis (Linnaeus 1758), belonging to the family Rhinocerotidae, is one of two extant species of African rhinoceros. It is a large herbivorous mammal endemic to Sub-Saharan Africa, with a broad historical range now significantly reduced. It is found along the east of Africa, from South-Sudan to the tip of South Africa, and west into Angola and Namibia. For permitting purposes in southern Africa, D. b. bicornis (the south-western black rhino) is recognised in Namibia, Angola, Botswana, and South Africa, and D. b. minor (the south-central black rhino) is recognised in South Africa, Zimbabwe, Eswatini, and Mozambique. There are four presumed subspecies of black rhino, with three currently considered extant (Balfour et al. 2025). This assessment adopted morphological and genetic evidence of four subspecies, providing basis to recognise three Evolutionarily Significant Units (ESUs) across the continent, having several contact zones, and no Genetic Management Units (GMUs) seen within them. Figure 1 visualises estimated ESUs and the presumed natural contact zones between them, as well as point data where samples were collected.

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Figure 1:

Natural distribution of black rhinoceros in Africa. Base colours show the current and historical distribution of the species across Africa. Historical range based on the IUCN distribution for the species is shown as hashed white regions. Current distribution and its management units are indicated by coloured regions. Western ESU is extinct. Points represent a locality which has been sampled for genetic data and correspond through colour to the ESU they are within. ESU ranges are based on genetic data of populations. Distribution data sources: ESU ranges estimated by Balfour et al. (2026). Historical range – Emslie, R. 2020. Diceros bicornis. The IUCN Red List of Threatened Species 2020, e.T6557A152728945. https://dx.doi.org/10.2305/IUCN.UK.2020-1.RLTS.T6557A152728945.en (Accessed 24th July 2026).

Management Level

Subspecies

There are currently four proposed black rhino subspecies, one of which is considered extinct.

  •  D. b. longipes (Western black rhino; extinct by 2011)

There are three extant subspecies among contemporary populations (Balfour et al. 2025).

  • D. b. michaeli (Eastern black rhino)
  • D. b. bicornis (South-Western black rhino)
  •  D. b. minor (South-Central black rhino)

The guidelines provided in this document are based on genetic data translated into the Evolutionarily Significant Units (ESUs) and Genetic Management Units (GMUs) listed below:

Evolutionarily Significant Units (ESUs)
  • Eastern Africa (EA) (D. b. michaeli)
  • South-West (SW) (D. b. bicornis)
  • South-Central (SC) (D. b. minor)
Genetic Management Units (GMUs)

No GMUs are recognised at present.

Management Boundaries

See Figure 1 for visual representation. Text descriptions follow.
Evolutionarily Significant Units (ESUs, based on proposed subspecies from Balfour et al. 2025)
  • Western Africa (WA): West of the Shari-Logone rivers*, Cameroon* and Nigeria* (extinct).
  • Eastern Africa (EA): Eritrea*, Ethiopia*, Kenya, Western Sudan*, Western South Sudan, Somalia*, Northern Tanzania, Uganda.
  • South-West (SW): Southern Angola, Western Botswana, Namibia, Western South Africa.
  • South-Central (SC): Eastern Angola, Eastern Botswana, Southern Democratic Republic of Congo*, Eswatini, Mozambique*, Malawi, North-Eastern South Africa, Tanzania, Zambia, Zimbabwe.

* Extinct in these countries.

Genetic Risk

  • Global Nc: 3,142 (Emslie 2020; Ferreira et al. 2024b).
  • South African Nc: 818 (Ferreira et al. 2025).
  • Genetic indicators are calculated at ESU level. These calculations are based on a best case scenario where gene flow is maintained.
  • If values are reported as a range, the average is used for subsequent calculations.

Table 1. Effective population size, Ne500 indicator, and confidence in the values calculated per ESU for black rhinoceros. Colour of the ESU label is linked to the colour used in Figure 1. Colour of Ne500 and confidence text corresponds to positive (green) or negative interpretation (orange/red). Overall Ne500 indicates the proportion of the total ESUs that have an Ne over 500. proportion of the total ESUs that have an Ne over 500.

Genetic Indicators
  • Ne500 indicator1
    • East Africa (EA) Individuals: 1044 (Emslie 2020). With assumed maturity percentage of 55.8 % (Emslie 2020), Nc: 583. Using an Nc:Ne ratio of 0.1 – 0.3, Ne = 58 – 175.
    • South-west (SW) Individuals: 2390 (Emslie 2020). With assumed maturity percentage of 55.8 % (Emslie 2020), Nc: 1,334. Using an Nc:Ne ratio of 0.1-0.3, Ne = 133 – 400.
    • South-central (SC) Individuals: 2,196 (Emslie 2020). With assumed maturity percentage of 55.8 % (Emslie 2020), Nc: 1,225. Using an Nc:Ne ratio of 0.1-0.3, Ne = 123 – 368.
  • Effective population sizes have been calculated with Bayesian skyline plot using mitochondria DNA (Moodley et al. 2017). This is for only a subset of countries so have been excluded from these guidelines. 

 

All three genetic management units have an Ne below 500 based on population census data. ESUs with Ne < 500 are highly susceptible to rapid loss of genetic diversity and are at high risk of extinction due to genetic threats. Although effective population size based on genetics was estimated in Moodley et al. 2017, here we calculated Ne using census data due to ambiguous population assignments; both methods result in an Ne500 value of 0.

 

  • Proportion of populations maintained (PM2):
    • The global populations of black rhinoceros comprise three ESUs relating to the three extant of the four proposed subspecies. Therefore, the proportion of populations maintained globally: 3/4 = 0.75.

 

Diversity Loss
  • Functional variation: There is risk of functional variation loss due to massive reduction in historical range causing fragmented/isolated populations. Due to this, there has likely been a loss of traits that were adapted to habitats the species formerly occupied. Ongoing poaching of the black rhinoceros especially in South Africa may further exacerbate this. Range expansion that is inconsistent with population and management boundaries (e.g. SE in Malawi and Zambia, and SC in northern and -western South Africa) may lead to the genetic erosion of locally evolved variation.
  • Divergent lineages: There is risk of losing divergent lineages due to small remaining population sizes in several areas of its range. The Western ESU is already extinct and the remaining ESUs have effective population sizes too small for long-term population maintenance.
Hybridisation/introgression
  • There is strong risk of hybridisation and introgression between black rhino subspecies due to past translocation (Moodley et al. 2017; Sánchez-Barreiro et al. 2023).
  • There is no risk of hybridisation with white rhinos as no inter-species crosses have been recorded in the wild or in captivity.
Lower turnover/constraints on adaptive opportunities
  • There has been a significant decrease in black rhino population densities since the 1970s (Mellya et al. 2025). Early colonisation and more recent land-use changes within the SC ESU has resulted in low levels of genetic diversity, and long term geographic isolation and possible ecological specialisation in an arid environment within the SW ESU may have resulted in a low effective population size and genetic diversity. These will have an impact on population turnover for the species, constraining adaptive opportunities.
In situ genetic threat level
  • In situ Risk (High)
    • Black rhinos exist in small, fragmented populations and are targets of poaching. Hybridisation between ESUs presents genetic risks in reduction of functional variation. Early colonisation and more recent land-use changes have resulted in low levels of genetic diversity for the SC ESU. Genetic diversity is low across the species and their ability to adapt quickly to environmental or population level changes is low. For more threats, see the IUCN Red List and South African Red List.
  • Confidence in in situ threat level
    • Confidence score (Moderate)

Confidence is moderate as the evaluation is based on scientific papers (Mellya et al. 2025; Moodley et al. 2017; Moodley and Robovsky 2025; Sánchez-Barreiro et al. 2023) and IUCN or regional assessment data from within the last decade (Emslie 2020; Ferreira et al. 2025). However, population numbers per ESU to calculate Ne500 were inconsistent and may not have captured the true presence of this species across the continent.

Ex situ representation
  • Black rhinos exist in captive populations within South Africa, North America, Europe, and Asia with 168 individuals across 63 institutions in 16 countries. The highest quantity is in North America with 56 individuals (Emslie et al. 2020).
  • Captive individuals in Europe predominantly from the SC ESU (Elsner-Gearing 2023).
  • South African captive SC ESU individuals show increased genetic load due to admixture between the southern ESUs (SC/SN); this admixture is extensive within the population (Elsner-Gearing 2023).

Figure 2. Effective population size compared to confidence in the value. Colour of points and labelling corresponds to the ESU in Figure 1 and Table 1. Dashed lines divide the x axis into above and below Ne500, and the y axis into low and high confidence. ESUs in the low confidence quadrant should be further surveyed to increase confidence in the evaluation. Those with high confidence below Ne500 should have increased genetic management. 

1 Proportion of populations within species with an effective population size (Ne) greater than 500
(https://www.gbf-indicators.org/metadata/headline/A-4)

2 Proportion of populations maintained within species
(https://ccgenetics.github.io/guidelines-genetic-diversity-indicators/docs/2_Theoretical_background/PM-indicator.html)

Management Guidelines

  • No translocation between ESUs across Africa, however, natural migration should not be hindered.
  • Southern ESUs (SW, SC) should be managed separately. The SW MU inhabits a water scarce region and it is still unknown whether this population contains local environmental adaptations. This is another reason to manage SW separately for now, despite its historical connection with the SC MU, to the east.
  • If populations are at imminent risk of extinction, due to reduced effective population size or inbreeding, Translocation should be permitted.
  • To make up a viable founding group 16 to 20 individuals should be used.
  • Efforts must be made to increase the effective population size of all ESUs to over 50 in for short term survival, and over 500 for long term genetic diversity.
  • To maintain within population heterozygosity, one breeding male should be introduced every seven years (Pers. comm. P. Goodman, 2021) or one male and one female should be introduced every 14 years.
  • Where genetic composition changes rapidly over relatively short geographic distances, maintaining close geographic proximity between source and recipient populations should be a high priority. Conversely, where genetic change is gradual over large distances, habitat similarity and ecological suitability may become relatively more important considerations than strict geographic proximity.

IUCN Status:

  • Global: Critically endangered (indicated below).
  • South Africa: Endangered.

Limitations & Assumptions:

  • Guidelines reflect the currently recognised black rhinoceros subspecies based on modern data. Studies including historical (museum samples) to investigate historical verses modern genetic diversity illustrate a greater number of ESUs that may have since been lost.

Priority Research:

  • Genetic sampling from smaller populations to properly assess current risk of inbreeding and rate of loss of genetic diversity.
  • The SW MU contains two monophyletic lineages which could possibly be classified as two separate MUs. Samples have been stored at the University of Pretoria (Onderstepoort) to conduct this work.
  • Samples from southern Namibia are still required to determine the natural southern limit of the SW population in that country. 
  • Future whole genome data are required for further genetic resolution and to determine the adaptive value of population genetic variation.
  • It is recommended that genetic monitoring studies be undertaken every 3-5 generations, if possible, to evaluate whether any changes in the genetic structure and diversity of this species have taken place, possibly warranting an update to these guidelines. Such studies would also contribute to the assessment of genetic indicators  under the Kunming-Montreal Global Biodiversity Framework. Note: such studies would not be to assess local pedigree, but rather broad population structure and diversity, and hence the overall genetic health of the species.

Cited references:

Consultation:

IUCN SSC Conservation Genetics Specialist Group
IUCN SSC African Rhino Specialist Group

Acknowledgements:

We are grateful to Drs Peter Goodman, Richard Emslie and Prof Oliver Ryder for their valuable comments and for taking the necessary time and effort to critically review the initial guidelines.

Queries:

If you have any additional questions related to these guidelines, please contact ConGen Africa at info@congenafrica.com.

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