Archived 2014 discussion: Oriental Bay-owl (Phodilus badius) is being split: list both P. badius and P. assimilis as Near Threatened?

This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for non-passerines

Lynx Edicions and BirdLife International will soon publish the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.

The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.

Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.

The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 1 of the checklist (for non-passerines) will begin to be incorporated into the 2014 Red List update, with the remainder, and those for passerines (which will appear in volume 2 of the checklist), to be incorporated into subsequent Red List updates.

Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.

Oriental Bay-owl Phodilus badius is being split into P. badius and P. assimilis, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, P. badius (BirdLife species factsheet) was listed as Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN criteria. This species was estimated to have an extremely large range, and hence did not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence of less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appeared to be stable, and hence the species did not approach the thresholds for Vulnerable under the population trend criterion (at least a 30% decline over ten years or three generations). The population size has not been quantified, but it was not believed to approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).

P. assimilis (incorporating ripleyi) is found in southern India and Sri Lanka, whilst P. badius (as defined following the taxonomic change, and incorporating all other forms) is found in South and South-East Asia, from eastern India and southern China, through the Thai-Malay Peninsula and throughout Sumatra, Borneo, Java and Bali. They inhabit primary and secondary forest, from lowland to montane areas, as well as some modified habitats (del Hoyo et al. 1999, König and Weick 2008). The threat of habitat destruction has been highlighted for both species (König and Weick 2008).

It is suggested that both species qualify as Near Threatened under criteria A2c+3c+4c, on the basis that they are suspected to be in moderately rapid population decline (approaching 30% over three generations [c.18 years]) owing to on-going habitat loss. The suspected rates of decline are not thought to be more rapid because of these species’ tolerance of some human-modified habitats.

Comments are invited on these suggested categories and further information would be welcomed.


del Hoyo, J., Elliott, A. and Sargatal, J. (1999) Handbook of the birds of the world, Vol 5: Barn- owls to Hummingbirds. Barcelona, Spain: Lynx Edicions.

König, C. and Weick, F. (2008) Owls of the World. Second Edition. London, UK: Christopher Helm.

Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. D., Fishpool, L. D. C. and Collar, N. J. (2010) Quantitative criteria for species delimitation. Ibis 152: 724–746.

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6 Responses to Archived 2014 discussion: Oriental Bay-owl (Phodilus badius) is being split: list both P. badius and P. assimilis as Near Threatened?

  1. Simon Mahood says:

    Agree for P. assimilis. However P. badius is a wide-ranging poorly known species that is probably commoner than usually thought. Because it favours areas with a high density of vertical stems it can often be found in regrowth. I suspect that this species is localised and not at any greater risk than any other forest dependent species with the same distribution.

  2. Praveen J says:

    1. Where can I find more on the taxonomic decision (score board) for this species ? Taxonomy section in Globally Threatened Birds does not list this species.

    Distribution: In the Western Ghats, P. assimilis is distributed from Sirsi (14.62 N) in the north till Kalakkad-Mundanthurai Tiger Reserve (KMTR) (8.5N) in the south, indicating almost the entire stretch of southern & central W. Ghats. Most records have come from Kerala (14 records till 2010 apart from regular haunts in Thattekkad WLS & adjoining areas – Birds of Kerala – Status & Distribution), wetter regions of Tamil Nadu (Anamalais, KMTR) and a couple of records from Karnataka (Sirsi, Coorg). Most of the records other than the Thattekkad ones (where roosts are well-known) are of recovered individuals, close to evergreen forests. Altitude ranges from as low as 60m to 1050m – and habitat is mostly evergreen but not always as Thattekkad sightings are also from moist-deciduous jungles.

    EOO Estimate: This indicates an EOO in excess of 5000 sq. km but less than 20000 – while AOO is largely unknown.

    Fragmentation: The bird has been recorded from six of the seven sub-clusters in Western ghats- Agasthyamalai, Periyar, Anamalai, Nilgiris, Talacauvery & Kudremukh. In these sub-clusters, the said habitat is nearly contiguous. Technically there are six sub-populations for this species, but it is uncertain whether gamut exchange / year will be within the threshold to categorize each of them as a true sub-population.

    Decline: Almost all records are from protected areas or reserve forests where there has not been any mass destruction in recent years – but habitat quality could have degraded in certain locations. It is true that number of recoveries in 1990-2000 period was more than 2000-2010 period – but that is only indicative and not easy to conclude as a definite decline. In regular haunts, sightings have not got any rarer – and hence the bird is probably tolerant to moderate levels of disturbances.

    In conclusion, in terms of range – it meets the Vulnerable criteria but it does not qualify supporting clauses for fragmentation, decline or fluctuations. If this is sufficient to list the taxa as Near-threatened, then perhaps it is.

  3. For the residual P. badius, I would not place it as among the more likely wide-ranging forest species to warrant NT status based on declines – as Simon Mahood says if this one warrants NT status based on declines, then so would most wide-ranging SE Asian evergreen forest birds occurring mostly below 600-700 m. When I did a lot of spotlight surveys for nocturnal mammals in Lao PDR in the 1990s Bay Owls were widespread and fairly numerous (not so much as scops owls, but much more than big owls, if numbers of calling birds detected reflect actual population levels) and from their locations are evidently widely occurring in heavily degraded and fragmented forest (probably not actual scrub, though). Thus any change in this one’s status should be undertaken in the context of re-examination of a large number of other species of similar altitudinal range.

  4. Frederic Goes says:

    I’m with Simon and Will on this species, at least regarding the Cambodian status. Although I state below “uncommon” it is indeed probably overlooked, and I don’t see why that species should be at any higher risk than many other forest species.

    STATUS (Cambodia): An uncommon resident of semi-evergreen and hill evergreen forests, from lower hills up to at least 1,200m. Also in pine forest at Kirirom NP. First record at 900m at Dak Dam (Mondolkiri) in January 1997 (Duckworth & Hedges 1998). Now known from a dozen scattered sites in the more densely forested parts of the country. In the southwest, fairly widespread above 600m throughout the Cardamom Mountains though not recorded at Bokor NP. A captive bird found at a Kep pagoda in February 2010 (H. Rainey pers. comm.). Scarce and local in the northwest (Kbal Spean) and the north (two sites in northern Preah Vihear). In the northeast, one record along the Sesan in January 2010 (FG) and known from southern Mondolkiri (Seima PF and Dak Dam).

  5. Joe Taylor says:

    Preliminary proposals

    Based on available information and comments posted above, our preliminary proposals for the 2014 Red List would be to treat:

    P. badius as Least Concern

    P. assimilis as Least Concern

    There is now a period for further comments until the final deadline of 31 March, after which recommended categorisations will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife and IUCN websites in mid-2014, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  6. Andy Symes says:

    Recommended categorisations to be put forward to IUCN

    Following further review, there have been no changes to our preliminary proposals for the 2014 Red List status of these species.

    The final categorisations will be published later in 2014, following further checking of information relevant to the assessments by BirdLife and IUCN.

Comments are closed.