BirdLife International factsheet for Metallic Starling.
Following a taxonomic reassessment, Metallic Starling (Aplonis metallica) has been split into Metallic Starling (A. metallica), and Purple-chinned Starling (A. circumscripta) (see Collar, 2018). The newly split Metallic Starling has a range extending from east Indonesia, through Papua New Guinea to Queensland in Australia. Purple-chinned Starling is found in the Tanimbar Islands and on Damar Island, Indonesia (Collar, 2018).
The exact habitat requirements for the newly split Purple-chinned Starling have not been investigated, but it is very likely to require lowland and montane forests, similar to Metallic Starling. Both species may also inhabit dry savannas, mangrove forests, and rural gardens (BirdLife International, 2020).
The population size of the pre-split species is unknown, but it is described as locally common to abundant, although it may be uncommon or rare on the Tanimbar Islands (Feare & Craig, 1998). There are not many threats known to the pre-split Metallic Starling, but as both species inhabit forests to some degree (BirdLife International, 2020), they may be at risk from deforestation.
The pre-split species was previously listed as Least Concern (BirdLife International 2020). However, following the taxonomic split, new range sizes suggest that both species warrant a thorough reassessment. We have therefore reassessed both species against each criterion here.
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 Metallic Starling has been recalculated to 3.8 years (Bird et al., 2020)*, and it is assumed that the generation length for the new Metallic and Purple-chinned Starlings are the same. Therefore, the rates of decline for these species are calculated over the length of 11.4 years.
Metallic Starling: The population trend for this species has not been directly estimated, and it is difficult to determine due to uncertainty over the impacts of habitat modification on population sizes (BirdLife International, 2020). The rate of tree cover loss across the post-split range for the Metallic Starling between 2000-2018 was 21% (Global Forest Watch, 2020). It isn’t clear whether this species tolerates degraded habitats, but as it is not wholly dependent on forests, it is probable that the population declines at a slightly slower rate than tree cover loss. However, even assuming that the population declines at the same rate as forest loss, this equates to a decline rate of 14% over the last three generations, which is too low to trigger the threatened threshold (≥ 30% reduction over 3 generations) under this criterion. Tracewski et al., (2016) also found insignificant rates of deforestation across the pre-split range during their analysis. Metallic Starling may therefore be considered Least Concern under Criterion A.
Purple-chinned Starling: This species may also be threatened by habitat loss. Based on Global Forest Watch (2020) data, the range for this species experienced a 6% tree cover loss between 2000-2018, a rate equating to <4% over three generations (assuming also here that the population declines at the same rate as forest loss), which is too low to trigger the threatened threshold here. Purple-chinned Starling may therefore be considered Least Concern under Criterion A.
Metallic Starling: The Extent of Occurrence (EOO) for the Metallic Starling is calculated to be 5,695,602 km². This is too high to trigger the threatened threshold (EOO <20,000 km²), and therefore, Metallic Starling may be considered Least Concern under Criterion B.
Purple-chinned Starling: The EOO for this newly identified species is calculated to be 41,412 km². This is too high to trigger the threatened threshold (EOO <20,000 km²), and therefore, Purple-chinned Starling may be considered Least Concern under Criterion B.
Metallic Starling: The population size for this species has not been directly estimated. However, a congener also described as common, the Asian Glossy Starling (A. panayensis), has been observed at densities of 6.18 birds/ha (see Martins et al., 2019). Assuming that A. metallica is found at similar densities, and only occupies 10% of its large range, this results in a population estimate far above the 10,000 mature individuals for listing as threatened under this criterion, and thus Metallic Starling may be considered Least Concern under Criterion C.
Purple-chinned Starling: This species is found on the Tanimbar and Damar islands, where the pre-split species was described as uncommon to rare. It is therefore assumed to persist at a lower population density than A. metallica. It also has a much smaller range. In order to fully assess Purple-chinned Starling against this criterion, we seek information on population size or population densities.
Metallic Starling: Based on the population density of a congener, the population estimates for this species is far higher than the threatened threshold of 1,000 mature individuals. Metallic Starling may therefore be considered Least Concern under Criterion D.
Purple-chinned Starling: While the population density for this species is unknown, given the size of its range, it is unlikely that there is <1,000 mature individuals, and therefore this species is tentatively considered Least Concern under Criterion D. We do however seek information relating to population size and density for this species.
To the best of our knowledge, no quantitative analysis has been carried out for these species and so they cannot be assessed against this criterion.
We therefore suggest that Metallic Starling (A. metallica) be listed as Least Concern and specifically ask for information on the population size on Purple-chinned Starling (A. circumscripta). Should there be no new information on the population size of this species, Purple-chinned Starling may tentatively 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.
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: Aplonis metallica. Downloaded from http://www.BirdLife.org on 21/05/2020
Collar, N.J., 2018, The taxonomic rank of Aplonis metallica circumscripta, Forktail, 34, pp. 14-18
Feare, C.; Craig, A. 1998. Starlings and Mynas. Christopher Helm, London.
Global Forest Watch. 2020. World Resources Institute. http://www.globalforestwatch.org (Accessed 21 May 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
Martins, C.O., Zakaria, M., Olaniyi, O.E., and Angela, U.O., 2018, Population Density of Avian Species in a Man-Made Wetland of Peninsular Malaysia, International Conference on Biodiversity, IOP Conf. Series: Earth and Environmental Science 269.
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.