Gola Malimbe (Malimbus ballmanni): Revise global status?

BirdLife International factsheet for Gola Malimbe.

This discussion was first published as part of the 2020 Red List update. At the time a decision regarding its status was pended, but to enable potential reassessment of this species as part of the 2021 Red List update this post remains open and the date of posting has been updated.

The Gola Malimbe (Malimbus ballmanni) is found in Africa, with a range that encompasses Sierra Leone, Guinea, Côte d’Ivoire, and Liberia. It inhabits lowland primary forest, lightly logged high forest, and very old secondary forest (BirdLife International, 2020).

The population size is estimated to 10,000-19,999 individuals, equating to 6,667-13,333 mature individuals. The population in Liberia’s Sapo National Park has recently been estimated at roughly 22,000 individuals (Freeman et al. 2018). Extrapolated data for the total population must be treated with caution as the species appears to be very rare and localised in the western part of its range (J. Lindsell in litt., 2007). Therefore, the overall population estimate remains at 10,000-19,999 individuals, but further surveys of other populations may alter this estimate in the future.

The only known threat to this species appears to be habitat loss and degradation resulting from commercial and illegal logging (Anon. 2000, via BirdLife International, 2020), and deforestation for agricultural and mining activities (Freeman et al., 2018).

Gola Malimbe has previously been considered Endangered under criterion A2c+3c+4c. However, recent data regarding the rate of forest loss may mean that this is no longer tenable and the species may warrant a change in Red List status. Gola Malimbe has therefore been reassessed here against all the criteria.

Criterion A: The population trend for this species has not been directly estimated. However, the only known threat for this species is habitat loss and degradation. Between 2000-2018, there was an estimated 7.4% reduction in tree cover across this species’s range (Global Forest Watch, 2020). 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 Gola Malimbe has been recalculated to 3.3 years (Bird et al., 2020)*. Therefore, the rates of reduction for this species are calculated over 10 years.

Assuming that the population size declines at the same rate as habitat loss, this equates to a 4.2% reduction over the last 10 years. Additionally, Tracewski et al. (2016) found negligible levels of deforestation in their analysis. A 10-year reduction rate of 4.2% is too low to trigger the threatened category (≥30% population size reduction) under this criterion. Gola Malimbe may therefore be considered Least Concern under criterion A.

Criterion B: The Extent of Occurrence (EOO) for this species is calculated to be 75,300 km². This is too high to trigger the threatened threshold (EOO <20,000 km²). Gola Malimbe may therefore be considered Least Concern under criterion B1. The Area of Occupancy (AOO) has not been quantified following IUCN Guidelines (IUCN Standards and Petitions Committee 2019), and therefore the species cannot be assessed against criterion B2.

Criterion C: The population size is estimated to be 6,667-13,333 mature individuals. Assuming that the true population is closer to the lower end of the estimate, this meets the threshold for Vulnerable (<10,000 mature individuals). However, in order to fully qualify as threatened under this criterion, other sub-criteria must be met. A continuing decline can be inferred from the continuing habitat loss. The number of subpopulations for this species is estimated to be 2-100, which precludes the criterion that all individuals are in one subpopulation. The rest of the subpopulation structure is unknown, and this species is not believed to experience any extreme fluctuations. As such, Gola Malimbe does not fully meet the requirements for classification as threatened here, and may therefore be considered Least Concern under criterion C.

Criterion D: The population size is estimated to be 6,667-13,333 mature individuals. This is too high to trigger the threatened threshold under this criterion (<1000 mature individuals). Gola Malimbe may therefore be considered Least Concern under criterion D.

Criterion E: To the best of our knowledge, no quantitative analysis has been carried out for this species. We therefore cannot assess Gola Malimbe against criterion E.

We therefore suggest that Gola Malimbe (Malimbus ballmanni) be listed as Least Concern. 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

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: Malimbus ballmani. Downloaded from http://www.BirdLife.org on 12/05/2020

Benedictus Freeman, Filibus Danjuma Dami & Mary Molokwu-Odozi (2018): Status of globally threatened birds of Sapo National Park, Liberia, Ostrich, DOI: 10.2989/00306525.2018.1502694

Global Forest Watch. 2020. World Resources Institute. http://www.globalforestwatch.org (Accessed 13 May 2020).

IUCN Standards and Petitions Committee. 2019. Guidelines for using the IUCN Red List Categories and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf

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.

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9 Responses to Gola Malimbe (Malimbus ballmanni): Revise global status?

  1. Hugo Rainey says:

    1. The population estimate for this species from the BirdLife datazone webpage is a preliminary estimate. Without further data this estimate should therefore be discarded as it is at least 13 years old and does not appear to have a sound basis.
    2. This species has a very localised distribution. For example: it was found by Demey & Rainey. (2006) in one patch in Diecke but not in another; Phalan did not find it in Zwedru; Demey & Rainey (2005) did not found it in Cavally although Gatter & Gardner (1993) (data from this paper may not be wholely reliable) had found it common at the site; and Lindsell said it was localised in the west of its range.
    3. Freeman et al. 2018 have some excellent data and analysis but they allude to the patchiness of the malimbe’s population: ‘The species was mostly recorded in
    the northern part of the park’ in Sapo. So, although their analysis looks high quality, given that they had to pool data from several species, we may want to consider whether the species is patchy at this site.

    I would therefore like to see this analysis reviewed with a more sound basis for an estimate for the global population.

  2. 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 ten years approximately 2.8% of tree cover with 75% canopy cover was lost from within the species’s range (Global Forest Watch 2020). This does not affect the above assessment under Criterion A.

  3. Ben Phalan says:

    Responding in relation to each criterion:

    Criterion A – the Global Forest Watch data do not provide a complete picture of forest degradation. Logging (legal and illegal) is widespread through this species’ range and tree cover loss does not reflect its full impact. An area can regrow to have 100% tree cover but have lost the large trees which create the habitat structure used by this species. Effects of logging on Gola Malimbe have not been quantified but could be severe. As anecdotal evidence for a (perhaps substantial) decline, Gatter described the species as “locally common” in the area near Zwedru in the 1980s. The species was not found at all during one month in the field there in 2013 (Collinson et al. 2018). Thus, we can expect that the decline has been greater than that calculated from Global Forest Watch data.

    Criterion B – It seems an analysis of AOO is needed for this species. Perhaps RSPB, who work with the species in Gola, might provide this? Also, the distribution map should be updated to include a new site for this species, discovered in 2011 in the West Nimba (Gba) Community Forest, Nimba County, Liberia (Dowsett-Lemaire & Phalan 2013).

    Criterion C – I suspect this species should qualify as Vulnerable with <10,000 mature individuals and continuing decline of at least 10% over ten years from forest loss compounded by logging impact. I agree with Hugo that more work is needed to incorporate patchiness into the estimate from Sapo, which is based on sightings of just 34 individual Gola Malimbes. It's a great start, but more work is needed to refine the population estimate for the park.

    Criterion D, E – nothing to add.

    My tentative suggestion would be to downlist this species to Vulnerable on basis of Criterion C1, pending more information.

    Collinson, J. M. et al. (2018) Taxonomic status of the Liberian Greenbul Phyllastrephus leucolepis and the conservation importance of the Cavalla Forest, Liberia. Journal of Ornithology, 159, 19–27.

    Dowsett-Lemaire, F., & Phalan, B. (2013) Nimba Western Area Iron Ore Concentrator Mining Project, Liberia. Environmental and Social Impact Assessment Volume 4, Part 2, Appendix 2: Ornithological Surveys in the Nimba Mountains in October-November 2011, with special reference to East Nimba Nature Reserve and the West Nimba (Gba) Community-Managed Forest. Report to URS for ArcelorMittal.

  4. Mark Hulme says:

    I agree with Hugo and Ben’s comments. I’ll add, regarding the patchiness of the population and the use of loss of forest cover as an indicator of threat where there might actually be a lot more going on, that the population in Sierra Leone appears to be very small and restricted to a small area of primary forest (Klop, Lindsell and Siaka 2010) despite extensive forest cover being present, and I never saw it anywhere other than at the published site. Immediately across the border in Liberia however, the species appears to be much more readily seen and in more more widely distributed across varied forest types (personal observation), though I’m not aware of a population estimate for this region. Given these apparent disparities, lack of understanding as to the reasons for these differences in occurrence across the range and the lack of confidence in the population estimate that Hugo and Ben refer to I would also recommend reviewing the analysis.

    Klop, E., Lindsell, J. A., & Siaka, A. M. (2010). The birds of Gola Forest and Tiwai Island, Sierra Leone. Malimbus, 32, 33-58.

  5. Jim Wardill says:

    From sabbaticals carried out in the Gola Forest Landscape (on both the Sierra Leone and Liberia sides) in 2013 (Simon Wotton) and 2017 (Jim Wardill), we found this species to be patchily distributed with no obvious reason for the local distribution. These recent findings fit with earlier research in this Western part of the species range from the 1970s (Field 1979) and 1980s (Gatter & Gardner 1993) that suggested a patchy distribution. We would agree with Hugo Rainey’s comment that estimates of population based on levels of forest cover cannot be made with confidence and more research on the ground would be required, particularly in the Eastern part of the species range to be able to come up with a more reliable population estimate. Freeman et al (2018) themselves note that further surveys are required in Sapo National Park to improve the density estimates for this species. This is particularly important given the patchy distribution of the species, the fact that surveys were geographically limited within the park, and that the majority of individuals occurred in the northern part of the park where Freeman et al identify increasing mining as a threat. A survey of Cavalla Forest in 2012 (specifically for Liberian Greenbul, Phalan 2013) failed to find any Gola Malimbes despite them being reported as locally common in this part of SE Liberia (Gatter & Gardner 1993).

    Whilst remote sensing gives estimates for forest loss, with your entry under Criterion A stating ‘Between 2000-2018, there was an estimated 7.4% reduction in tree cover across this species’ range (Global Forest Watch, 2020)’ – remaining tree cover does not necessarily equate to Gola Malimbe distribution, as selective logging is thought to be a factor in the absence of this species from parts of its range. Whilst habitat degradation is listed as a threat to the species, GFW data do not reliably detect such degradation and we would therefore caution against assuming that population declines at the same rate as habitat loss. This may mean that the AOO, not quantified here due to the limited data, may be considerably smaller than the EOO (Criterion B). Tracewski et al (2016) did not use their analysis for suggested downlisting of species for this reason and noted that “species may have an AOO that is considerably smaller than our maximum estimate owing to highly specific habitat requirements”. Assessments of forest quality in Central and Eastern Liberia, based on on-the-ground fieldwork and observations would be another important part of a case for down-listing the species.

    Given the vulnerability of the Upper Guinea forests to clearance and mining operations, particularly in Sierra Leone and Liberia (slowed in recent decades only in Liberia and Sierra Leone due to Civil War and the Ebola outbreak), our view is any downgrading of this species’ threat status would be premature, and that it should not drop below Vulnerable unless more evidence is gathered and a level of confidence of elimination (e.g. through a logging moratorium) of future threats to the forest is achieved.

    Jim Wardill, Simon Wotton, Fiona Sanderson (RSPB)

  6. 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

  7. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, in the absence of a more conclusive population estimate, this species is precautionarily assumed to have fewer than 10,000 mature individuals. It is not possible to list the Gola Malimbe as threatened under Criterion C1, as the rate of population decline is only suspected, and this criterion requires the rate of decline to be observed, estimated, or projected. However, it is tentatively assumed that the mature individuals are part of the same genetic subpopulation, due to dispersal ability and its tolerance of lightly logged forest.

    Our preliminary proposal for the 2020 Red List would be to list Gola Malimbe as Vulnerable under Criterion C2a(ii).

    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

  8. Paul Robinson says:

    Criterion A. My comment is in support of Ben Phalan and the RSPB comments on the inaccuracy of Global Forest Watch (GFW) data for habitat degradation and loss. GFW uses the Hansen forest cover data (https://science.sciencemag.org/content/342/6160/850). This is good for some purposes, but has a definition of forest that follows the FAO; any vegetation with a canopy of >5m. This therefore includes many habitats that are not the habitat of Gola Malimbe (palm oil plantations, secondary regrowth etc) and so cannot be used as a measure of the extent of potentially occupied habitat for either range or occupancy assessment. A second limitation is the 30m Landsat resolution, which will not detect smaller scale change even within the broad definition of forest. A recent manual check of Hansen against finer resolution Spot data showed 80-90% of forest loss in a sample area in Ghana (https://ecometrica.com/wp-content/uploads/2015/08/UMD_accuracy_assessment_website_report_Final.pdf) was not detected by Hansen. I have no direct experience of Gola Malimbe habitat, but in northern Sierra Leone where I work the Hansen (hence GFW) data does not, and is not designed to, separate riverine forest (similar to Golo Malimbe habitat) from savanna woodland (not!) and so for example hugely overestimates the extent of suitable habitat for yellow-casqued hornbill, present in riverine forest and absent in savanna woodland. In conclusion this line of evidence is not reliable as a proxy for any measure of habitat suitability for Gola Malimbe: species that, as much as is known, requires high canopy forest.

  9. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    Based on available information, our proposal for the 2020 Red List is to pend the decision on this species and keep the discussion open until 2021, while leaving the current Red List category unchanged in the 2020 update.

    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.

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