Tanimbar Scrubfowl (Megapodius tenimberensis): revise global status?

BirdLife species factsheet for Tanimbar Scrubfowl

Tanimbar Scrubfowl (Megapodius tenimberensis) is endemic to Indonesia, where it is restricted to Yamdena Island (Coates and Bishop 1997). The global population is estimated at 1,000-10,000 individuals (del Hoyo et al. 1994), which roughly equates to 670-6,700 mature individuals.

The species is sparsely distributed (Bishop and Brickle 1998). It occurs at moderate density in the lowlands of the island, where it inhabits primary, old selectively logged and tall secondary, semi-evergreen forest. Tanimbar Scrubfowl requires unfragmented habitat and is therefore severely threatened by forest loss on Yamdena. It is additionally threatened by hunting for food, egg collecting and introduced predators, which are evident mainly in the southern part of the island where forest clearance is most prevalent (K. D. Bishop in litt. 2006, del Hoyo et al. 2019).

Tanimbar Scrubfowl is currently listed as Near Threatened, approaching the threshold for listing as threatened under Criterion B1ab(iii) (BirdLife International 2019). However, using available information regarding the amount of suitable habitat and the population size, this species appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

Criterion A – The population is suspected by the in decline due to loss and degradation of its habitat, but the trend has not been directly estimated. Tracewski et al. (2016) measured the forest loss within the species’s range between 2000 and 2012 as c. 49 km2. This roughly equates to a rate of forest loss of 2.7% over three generations (12 years) for this species. Threats known for Tanimbar Scrubfowl include forest clearance and hunting. Thus, given the additional threat from hunting, we can assume that the rate of population decline may be larger than the rate of forest loss. However, even under this assumption, this rate is likely too low to meet the threshold for Vulnerable under this criterion (≥ 30% over 10 years). Therefore, Tanimbar Scrubfowl may be listed as Least Concern under Criterion A.

Criterion B – The Extent of Occurrence (EOO) has been calculated as 4,000 km2, which meets the threshold for listing as Endangered under Criterion B1 (EOO < 5,000 km2). Tracewski et al. (2016) estimated the remaining tree area within the species’s range to be c.1,800 km2. We can tentatively assume that for a forest-dependent species like Tanimbar Scrubfowl, the area of forested habitat equals the maximum Area of Occupancy (AOO); as such the maximum AOO meets the threshold for Vulnerable under Criterion B2 (AOO < 2,000 km2). However, to be listed under Criterion B, at least two of three further conditions have to be met.

The species is widely distributed across Yamdena Island and it is thus assumed to occur at > 10 locations* (BirdLife International 2019). However, it is possible that Tanimbar Scrubfowl approaches this threshold. Even though its habitat shows some degree of fragmentation particularly in the south of Yamdena (Global Forest Watch 2014), the species should not be considered severely fragmented per IUCN definition (see IUCN Standards and Petitions Subcommittee 2017). Tanimbar Scrubfowl therefore does not meet condition (a) (severely fragmented or ≤ 10 locations), but likely approaches it. AOO, area, extent and/or quality of habitat as well as the number of mature individuals are declining, and hence the species meets condition (b) under subconditions (ii,iii,v). However, Tanimbar Scrubfowl does not undergo extreme fluctuations and so does not meet condition (c).

Therefore, even though Tanimbar Scrubfowl occurs in a very small range and consequently in restricted EOO and AOO, it does not trigger sufficient conditions for listing as Vulnerable under criterion B, but it meets one condition and approaches the second.  As such, it may be listed as Near Threatened under Criteria B1ab(ii,iii,v)+2ab(ii,iii,v).

Criterion C – The population size of Tanimbar Scrubfowl has been estimated at 670-6,700 mature individuals. This meets the threshold for Vulnerable (< 10,000 mature individuals) or even Endangered (< 2,500 mature individuals), assuming that the true population size is closer to the lower end of the estimate. However, in order to be listed under Criterion C, other conditions have to be met.

The rate of decline in Tanimbar Scrubfowl has not been directly estimated, and so Criterion C1 cannot be used to trigger a listing as threatened. Instead, the population decline can be inferred from habitat loss (Tracewski et al. 2016). The species is not known to undergo extreme fluctuations, so it does not trigger the conditions for Criterion C2b. It thus depends on the species’s subpopulation structure whether it qualifies for listing as Vulnerable under condition (a). There is no information on the number of subpopulations of Tanimbar Scrubfowl. However, assuming that the global population size is closer to the lower end of the estimate, no subpopulation would contain more than 1,000 mature individuals, and the species would qualify for Vulnerable. Therefore tentatively, Tanimbar Scrubfowl may be listed as Vulnerable under Criterion C2a(i).

Criterion D – The global population of Tanimbar Scrubfowl has been estimated to number 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 classifying as threatened (< 1,000 mature individuals). Therefore, it may precautionarily be listed as Vulnerable under Criterion D1.

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 Tanimbar Scrubfowl (Megapodius tenimberensis) be listed as Vulnerable under Criteria C2a(i); D1. We welcome any comments on this 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 its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic.

*The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

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: Megapodius tenimberensis. http://www.birdlife.org. (Accessed 15 February 2019).

Bishop, D.; Brickle, N.W. 1998. An annotated checklist of the birds of the Tanimbar Islands. Kukila 10: 115-150.

Coates, B. J.; Bishop, K. D. 1997. A Guide to the Birds of Wallacea. Dove Publications, Alderley, Australia.

del Hoyo, J.; Collar, N.; Christie, D. A. 2019. Tanimbar Scrubfowl (Megapodius tenimberensis). 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/467084 (Accessed 15 February 2019).

del Hoyo, J.; Elliott, A.; Sargatal, J. 1994. Handbook of the Birds of the World, vol. 2: New World Vultures to Guineafowl. Lynx Edicions, Barcelona, Spain.

Global Forest Watch. 2014. World Resources Institute. www.globalforestwatch.org (Accessed 14 February 2019).

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.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. 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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1 Response to Tanimbar Scrubfowl (Megapodius tenimberensis): revise global status?

  1. Rob Martin (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2019 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.

    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.

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