Archived 2020 topic: Metallic Starling (Aplonis metallica) is being split: assessment of the newly recognised taxa.

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.

Criterion A:

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.

Criterion B:

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.

Criterion C:

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.

Criterion D:

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.

Criterion E:

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.

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: 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.

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8 Responses to Archived 2020 topic: Metallic Starling (Aplonis metallica) is being split: assessment of the newly recognised taxa.

  1. James Eaton says:

    Having visited Tanimbars on eight occasions, only once have I encountered a colony of Purple-chinned Starlings, the rest of the time just small groups of us to 10. Tanimbar Starling is by far the more numerous species (which is classified as Near-threatened), crudely, at a ration of 20 to 1 on each of my visits. Yamdena is gradually suffering substantial forest lost, as with much of lowland Eastern Indonesia as part of an economic drive from the central government, and large trees, required for the colonies are disappearing fast.

    In six visits, I have yet to encounter a single bird on Damar.

    James

  2. Guy Dutson says:

    Metallic Starling is abundant in lowland forests in many Melanesian islands, often in comparable or higher densities in secondary habitats including coconut plantations and mangroves. It is however restricted to lowlands and would be impacted by land clearance such as for oil palm plantations on New Guinea. Population densities measured approximately at 3 contact s/ ha in primary lowland forest and 1-7-7.5 contacts / ha in various degraded lowland habitats and mangroves on Kolombangara (Buckingham et al 1990). = Least Concern

  3. Bas van Balen says:

    In November last year I went to Tanimbar for the first time, Tanimbar Starling was indeed far more common than Purple-chinned. The latter was found in two different colonies along a 1 km transect in the southern part of Yamdena. The scarcity of records reported by others for Tanimbar may suggest a very local occurrence, or seasonality of occurrence, in which the starlings inhabit the Tanimbar’s satellite islands (rarely visited by ornithologists) during most of the year?

  4. Robert Davis says:

    Agree with the listing. This was the third most common bird recorded in around 40 hours of oil palm surveys we did in New Britain (Reporting rate of 71.95%) and was recorded in 60% of all forest surveys.

  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 proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to list

    Metallic Starling as Least Concern
    Purple-chinned Starling as Least Concern.

    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.

  7. James Eaton says:

    Regarding Purple-chinned Starling, from Collar 2018:

    Somewhat troublingly, the species was not found on Damar during 30 days of fieldwork in 2001, when rats, possibly Ship Rats Rattus rattus, were found to be abundant in forest and suspected of involvement in the ‘decline of colonial-nesting species such as Metallic Starling’ (Trainor 2007). Moreover, three visits (one in 2009, two in 2011) yielded no reports of the species on the larger island of Babar, which lies midway between Damar and the Tanimbar Islands (Trainor & Verbelen 2013). Fortunately, despite the failure to find it on Yamdena 20 years ago, prompting the consideration that it might be confined to one or a small number of outlying islands in the Tanimbar group (Bishop & Brickle 1998), it has been seen there in recent years, including a colony of 20 pairs in October 2018 (J. A. Eaton in litt. 2018). Nevertheless, research to clarify its conservation status and in particular its vulnerability to rats is clearly a pressing need.

    Given that it does appear to have disappeared from one remote island, Damar (30 day field work + 6 additional visits, since 2000), and observer have noted its scarcity, particularly in comparison to the Near-threatened Tanimbar Starling on Tanimbar, Least Concern, the same threat status as the widespread, abundant Metallic Starling might be worth of reconsideration.

    Regards

    James

  8. Red List Team (BirdLife International) says:

    Recommended categorisations to be put forward to IUCN

    Following further review, the recommended categorisation for one of these species has changed.

    Metallic Starling is recommended to be listed as Least Concern.
    Based on a suspected decline and an inferred population size that is unlikely to exceed 10,000 mature individuals, Purple-chinned Starling is recommended to be listed as Near Threatened, nearly meeting the threshold for Criterion C2a(i).

    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.

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