Archived 2019 topic: Monteiro’s Bush-shrike (Malaconotus monteiri): revise global status?

BirdLife species factsheet for Monteiro’s Bush-shrike

Monteiro’s Bush-shrike (Malaconotus monteiri) is known from a small number of records from a few sites in Angola and Cameroon. In Angola, recent surveys found it to be relatively rare (Cáceres et al. 2015), while other studies found in more widespread and at least locally very common (Mills and Dean 2007, Mills 2010). The species’s stronghold appears to be the Kumbira Forest Reserve in the Escarpment Zone (Fry and Sharpe 2018). Its distribution in Cameroon is somewhat unclear; while one specimen collected in the 19th century originated from Mt Cameroon, more recent records of the species are thought to relate to the very similar Grey-headed Bush-shrike (Malaconotus blanchoti) and are perhaps best considered unconfirmed (Mills 2010).

The population size has not been quantified. However, we can derive a preliminary estimate based on the population estimate of the closely related Bokmakierie (Telophorus zeylonus), which occurs in a much larger global range, is described as ‘not uncommon’ in Angola and estimated to number 670-6,700 mature individuals (Dean 2000, BirdLife International 2019, see also eBird 2019). Unless more detailed information becomes available, we can tentatively place Monteiro’s Bush-shrike in the same band of 670-6,700 mature individuals.

The ecological requirements of Monteiro’s Bush-shrike are poorly known. It occurs in drier forest above and below the main scarp, but not in the moister forest on the scarp. It shows some tolerance of habitat modification and transitional habitats, having been recorded in forest under-planted with coffee, moist secondary growth, coffee plantations, thickets and riverine forest (P. Vaz Pinto in litt. 2012).

Monteiro’s Bush-shrike is thought to be in decline due to the ongoing destruction of its habitat. Considerable forest loss has occurred on the Angolan scarp already in the last decades. The major driver of forest loss is the conversion of forests into agricultural land by subsistence farmers. Canopy trees and forest undergrowth, but also overgrown coffee plantations and secondary growth have been removed to give way for cultivations of banana, manioc, sweet potatoes, cassava and maize (W. R. J. Dean in litt. 1999, F. Olmos in litt. 2011). In the species’s stronghold in the Kumbira Forest Reserve, however, forest cover increased slightly between 1989 and 2010 (Fry and Sharpe 2018).

Currently, Monteiro’s Bush-shrike is listed as Near Threatened, approaching the threshold for listing as Vulnerable under Criterion B1ab(i,ii,iii,v), indicating a very small Extent of Occurrence (EOO) and declines in habitat availability and population size.

Following IUCN guidelines, the EOO for this species has been re-calculated using a Minimum Convex Polygon, which is “the smallest polygon in which no internal angle exceeds 180 degrees and which contains all the sites of occurrence” (IUCN 2001, 2012, Joppa et al. 2016). The records for Cameroun have been treated as unconfirmed and the presence of the taxon uncertain per IUCN Guidelines (IUCN 2001, 2012). After re-calculating the EOO, Monteiro’s Bush-shrike appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

The initial topic on this analysis can be found here.

Criterion A – Tracewski et al. (2016) measured the forest loss within this species’s range between 2000 and 2012 as c. 450 km2. This roughly equates to a rate of forest loss of 3.4% over three generations (13.2 years) for this species, with the assumption that habitat loss has continued at the same rate to the present day. As the species shows some tolerance to habitat degradation, population changes may be lower than forest cover change, and it is unlikely that the rate of population decline approaches the threshold for Vulnerable. Therefore, Monteiro’s Bush-shrike may be listed as Least Concern under Criterion A.

Criterion B – Using a Minimum Convex Polygon, the Extent of Occurrence (EOO) has been calculated as 44,800 km2. Thus, Monteiro’s Bush-shrike may be listed as Least Concern under Criterion B1. The Area of Occupancy (AOO) has not been estimated, and thus the species cannot be assessed against Criterion B2.

Criterion C – The population size of Monteiro’s Bush-shrike is preliminarily estimated at 670-6,700 mature individuals and assumed to undergo a slow, but continuing decline. This meets the threshold for listing as threatened under Criterion C, as long as at least one other condition is met. The rate of decline is inferred from the rate of forest loss, and hence the species cannot be accurately compared against Criterion C1. The subpopulation structure has not been assessed. However, records on eBird suggest that the species forms at least two disjunct subpopulations in the Kumbira Forest Reserve and in the Quiçama National Park (eBird 2019); thus the species does not meet condition a(ii). While we have no information on the size of these subpopulations, given the overall population size it is highly likely that each contains less than 1,000 mature individuals. Hence Monteiro’s Bush-shrike may be listed as Vulnerable under Criterion C2a(i).

Criterion D – The population size preliminarily estimated at 670-6,700 mature individuals. Assuming that the true population size is closer to the lower end of the estimate, the species meets the threshold for listing as Vulnerable under Criterion D1. The AOO and number of locations have not been quantified, and therefore the species cannot be assessed against Criterion D2.

Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.

Therefore, it is proposed that Monteiro’s Bush-shrike (Malaconotus monteiri) be listed as Vulnerable under Criteria C2a(i); D1. We welcome any comments on this proposed listing and specifically request up-to-date information on the population size.

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.

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

BirdLife International. 2019. Species factsheet: Telophorus zeylonus. http://www.birdlife.org (Accessed 03/05/2019).

Cáceres, A.; Melo, M.; Barlow, J.; Cardoso, P.; Maiato F.; Mills, M. S. L. 2015. Threatened birds of the Angolan Central Escarpment: Distribution and response to habitat change at Kumbira Forest. Oryx 49: 727-734.

Dean,W. R. J. 2000. The birds of Angola. British Ornithologists’ Union, Tring, U.K.

eBird. 2019. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, N.Y., U.S.A. http://www.ebird.org (Accessed on 03/05/2019).

Fry, H.; Sharpe, C.J. 2018. Monteiro’s Bush-shrike (Malaconotus monteiri). 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, Spain. https://www.hbw.com/node/60501 (Accessed 14 September 2018).

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. www.iucnredlist.org/technical-documents/categories-and-criteria.

Joppa, L.N.; Butchart, S.H.M.; Hoffmann, M.; Bachman, S.P.; Akçakaya, H.R.; Moat, J.F.; Böhm, M.; Holland, R.A.; Newton, A.; Polidoro, B.; Hughes, A. 2016. Impact of alternative metrics on estimates of extent of occurrence for extinction risk assessment. Conservation Biology 30: 362-370.

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

Mills, M.S.L.; Dean, W.R.J. 2007. Notes on Angolan birds: New country records, range extensions and taxonomic questions. Ostrich 78: 55-63. 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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3 Responses to Archived 2019 topic: Monteiro’s Bush-shrike (Malaconotus monteiri): revise global status?

  1. Michael Mills says:

    Just a few comments that I hope will assist your assessment.
    1. Based on continued observation at Kumbira Forest and a field trip to new sites along the Angolan escarpment last week, the rate of forest loss along the main central escarpment is several fold higher now than it was in 2000-2012. I would estimate that 80% of forest loss at Kumbira that has occurred since my first visit in 2003, has occurred after 2012. Commercial logging, commercial farming (especially bananas) and charcoal production have emerged as serious threats to remaining forest.
    2. Monteiro’s Bushshrike is nearly extinct at Kumbira Forest now. It has declined greatly since 2010. So Kumbira is no longer a stronghold.
    3. We are generally finding Monteiro’s Bushshrike to be fairly widespread, and it is still fairly common locally (I recorded 5 in one day last week), even in areas fairly far away from the main central escarpment. It certainly occurs at the base of the northern escarpment. The extend of occurrence is probably wider than previously thought, but not as high as your estimate.
    4. Based on observation over the past 5 years I would estimate population size to be at least at the upper end of your estimate, if not higher
    5. In summary, I would think that it could qualify as Vulnerable only on rate of decline. Along the main part of the central escarpment rate of decline is probably quite high, but in other areas it will be much lower.
    6. I’m not sure what sites you used to calculate the EOO, but is seems to be several folds higher than my estimate (Mills 2010) of 8000 km2.

  2. Rob Martin (BirdLife International) says:

    Many thanks for the detailed and helpful comment. From this it seems unlikely that the population estimate is below the threshold for listing as Vulnerable under Criterion C. Noted that the rate of decline may also be higher, but it again does not appear to exceed the thresholds for listing as Vulnerable.
    Do note the manner in which Extent Of Occurrence is calculated, the Minimum Convex Polygon is a crude shape that encompasses the whole area believed to represent occupied or probably occupied range, hence does not reflect the extent of habitat but the spread of extinction risk from the point of view of a location based threat.

  3. Rob Martin (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2019 Red List would be to continue to list Monteiro’s Bush-shrike as Near Threatened as it is suspected to approach the thresholds for listing 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 those in the initial proposal.

    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.