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.
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.