Archived 2020 topic: Gabela Bush-shrike (Laniarius amboimensis): Revise global status?

BirdLife International factsheet for Gabela Bush-shrike.

Gabela Bush-shrike is endemic to Angola, and inhabits escarpment forests, secondary forest, and degraded farmbush (Fry, 2020). The main threat to Gabela Bush-shrike is habitat loss and degradation through agricultural practices (Mills, 2010). The population of this species was thought to be very small, estimated to be 250-999 mature individuals (BirdLife International, 2020), but it is now evident this is based on incorrect estimates of range size, and therefore is likely to be an underestimate.

As such, Gabela Bush-shrike has been considered Endangered under criterion C2a(i). However new information, particularly relating to the estimation of its population size, may warrant a change in Red List category. We have therefore reassessed this species here against all the criteria.

Criterion A: The population trend for this species is thought to be declining, but the rate of that trend has not been directly quantified. 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 Gabela Bush-shrike has been recalculated to 3 years (Bird et al., 2020)*. Therefore, the rates of reduction for this species are calculated over 10 years.

The main threat to this species is habitat loss through deforestation. Data from Global Forest Watch (2020) and Tracewksi et al. (2016) estimated that between 2000 and 2012, this species experienced a rate of forest loss of 1.7% over the last 10 years. Assuming that the population declines at the same rate, this does not meet the threshold (≥30% reduction in 10 years) to be classified as threatened. This species can therefore be considered Least Concern under this criterion.

Criterion B: The Extent of Occurrence for this species is estimated to be 5,009 km², which reaches the threshold for classification as Vulnerable (EOO < 20,000 km²). The maximum Area of Occupancy (AOO) for this species is estimated to be 3,612 km², which does not meet the threshold (AOO <2,000 km²) for classification as threatened under sub-criterion B2. In order to fully qualify for classification under criterion B1, other sub-criteria must be met.

The number of locations for this species is estimated to be 6 (BirdLife International, 2020), which remains below the threshold for Vulnerable (≤10 locations). This species is not believed to experience any extreme fluctuations, but it continues to experience ongoing habitat degradation. Gabela Bush-shrike may therefore be considered Vulnerable under criterion B1ab(iii).

Criterion C: The population size for Gabela Bush-shrike has not been directly estimated. However, other Laniarius species have been observed at population densities of 0.2-1.6 breeding pairs/km² (see Kopij, 2019). Assuming that Gabela Bush-shrike occurs in similar densities, when applied to the calculated maximum AOO, this produces a population estimate of 1,400-11,600 mature individuals. Assuming the true population size is near the lower end of the estimate, this reaches the threshold (<10,000 mature individuals) for classification as Vulnerable. However, in order to fully classify under this criteria, other sub-criteria must be met. Continuing decline can be inferred from the continuing habitat degradation, and the species is not believed to experience extreme fluctuations in numbers of mature individuals.

This species is not believed to exist in one subpopulation as there are an estimated 2-100 subpopulations (BirdLife International, 2020). Depending on the true population size and the true number of subpopulations, it is possible (but not certain) that the largest subpopulation contains <1,000 mature individuals. As such, Gabela Bush-shrike may be considered Near Threatened, approaching the threshold for listing as threatened under criterion C2a(i).

Criterion D: The population estimate is too high to trigger a threatened category under this criterion (< 1,000 mature individuals). Gabela Bush-shrike may therefore be considered Least Concern under this criterion.

Criterion E: To the best of our knowledge, no quantitative analysis has been undertaken for this species. Therefore, we cannot assess this species against this criterion.

We therefore suggest that Gabela Bush-shrike (Laniarius amboimensis) be listed as Vulnerable under criterion B1ab(iii). We welcome any comments to the proposed listing, particularly information on population size, density, or subpopulation structure. 

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic. 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: Laniarius amboimensis. Downloaded from http://www.BirdLife.org on 29/04/2020

Fry, H. (2020). Gabela Bush-shrike (Laniarius amboimensis). 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/60523 on 29 April 2020).

Global Forest Watch. 2020. World Resources Institute. http://www.globalforestwatch.org (Accessed 29/04/2020).

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

Kopij, G., 2019, Structure of avian communities in a mosaic of built-up and semi-natural urbanised habitats in Katima Mulilo town Namibia, Welwistchia International Journal of Agricultural Sciences, 1, pp: 68-75


Mills, M. S. L. 2010. Angola’s central scarp forests: patterns of bird diversity and conservation threats. Biodiversity and Conservation 19(7): 1883-1903.

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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7 Responses to Archived 2020 topic: Gabela Bush-shrike (Laniarius amboimensis): Revise global status?

  1. Michael Mills says:

    At Kumbira Forest, the best known site for the species, we have seen close to a 100% decline in 9 years (2010 to 2019). In 2010 it was recorded at 42 out of 203 sample points. In 2018 I revisited at least 20 of these points and found zero Gabela Bushshrikes, at the same season. I have not seen Gabela Bushshrike at Kumbira Forest since 2017. This site is not atypical of what we are seeing across the entire escarpment. More extensive surveys in 2018 and 2019 to various sites along the central escarpment turned up three pairs of the bird in about 10 days of searching, whereas 15 years ago I could find 5-10 pairs in a morning at Kumbira, and several pairs around Bango where I now know of one pair only.

    I’ve not read the papers Global Forest Watch (2020) and Tracewksi et al. (2016) that estimated that between 2000 and 2012 this species experienced a rate of forest loss of 1.7% over the last 10 years. However, I can assure you that they are in no way linked to reality on the ground. VAST areas of suitable habitat have been lost in the last 5-10 years.

    In my opinion this is Angola’s most threatened bird. Please consult Lincoln Fishpool (who visited some of these sites with me in 2019) and Pedro Vaz Pinto (who has searched for it extensively along the central escarpment too).

    There certainly is no sub-population with >1000 pairs and I highly suspect that there are fewer than a total of 1000 pairs, globally. Please contact me directly if you wish to receive further details.

  2. Hi,

    I must say that I am shocked with the proposal to downlist Laniarius amboinensis from Endangered to Vulnerable status. I believe that would be a most unfortunate decision and a blunder. If anything, it should be uplisted.
    I’m an Angolan biologist with 20 years of field experience which includes a good deal of birdwatching in the key areas. Of all the Angolan endemic species this is surely the rarest one and appearing to be declining more rapidly.
    I cannot provide accurate estimates for densities, total population size and distribution area but I suspect these were all grossly overestimated in this assessment. I’m also convinced the degree of threat was seriously underestimated, and I’m saying this based on field knowledge. There is absolutely noo way that habitat loss in 10 years measured at a deforestation rate of 1.7% even remotely reflects reality. Rather, the very few places where the species was known to occur until recently have been hammered severely.
    This is a species that between 2003 and 2010 could be easily observed in the forests of Kumbira (arguably the prime site). Remarkably the species almost completely disappeared since 2010. After a huge effort done for several weeks in 2019 I was elated to have located two pairs in a remote valley in Kumbira – the first I’ve seen in years! I know of at least another pair present 50kms south of here, and surveys conducted even further south and in intermediate regions produced no results earlier this year. So far, the perceived rate of decline of this species I would consider it to be frightening and even somewhat mysterious. I don’t question that it is possible, and even likely, that there may be some sites on where the species is still locally common, but so far no one has been able to find these sites and I’m convinced that less than 10 pairs have actually been observed by birdwatchers coming to Angola very the past several years. As likely as it may be that many more individuals may still exist, this remains unproven!
    I would say that it is a top priority to conduct a comprehensive and exhaustive survey to document the species ASAP. Until then I think it would be not only very wrong but reckless to downlist its conservation status.

  3. Lincoln Fishpool says:

    Although on the basis of much less authority than either Michael or Pedro, I too feel this proposal is ill-founded. During my visit to Angola in October 2019 I saw (and heard), in company with Michael, only one pair of Gabela Bush-shrike, despite spending some three days birding in suitable habitat. Michael’s concern for the status of bird meant that we were actively searching for this species during this time – regular playback of recordings in the hope of provoking a response etc. – as opposed to passively hoping to see it along with other forest species. These surveys took in places where Michael had recorded the bird previously, as well as forest patches hitherto unvisited by him. In all of these, significant levels of recent forest clearance were evident. However, this latter cannot be the only immediate explanation for the decline observed by Michael and Pedro, as the shrike appeared to be absent from much of the remaining forest.

  4. 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 6.5% 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.

  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 proposals

    Based on available information, this species appears to have a sparse distribution with a small population. Due to the recent increase in declines, and in the absence of more conclusive estimates, this species is precautionarily suspected to have <250 mature individuals in each subpopulation.

    Our preliminary proposal for the 2020 Red List would therefore be to retain Gabela Bush-shrike as Endangered under Criterion C2a(i).

    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. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Gabela Bush-shrike is recommended to be listed as Endangered under Criterion C2a(i).

    Many thanks for everyone who contributed to the 2020 GTB Forum process. 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.

Comments are closed.