Archived 2014 discussion: Long-billed Partridge (Rhizothera longirostris) is being split: list R. dulitensis as Vulnerable and R. longirostris 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.

Long-billed Partridge Rhizothera longirostris is being split into R. longirostris and R. dulitensis following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, R. longirostris (BirdLife species factsheet) was listed as Near Threatened under criteria A2c+3c+4c, on the basis that it was suspected to be undergoing a moderately rapid population decline (approaching 30% over three generations [c.12 years]) owing to on-going habitat loss and degradation.

R. dulitensis is known to inhabit forest in a few montane areas in northern Borneo, and appears to have a disjunct range (Madge and McGowan 2002, Mann 2008, Myers 2009, Phillipps and Phillipps 2011). It may qualify as Vulnerable under criterion C2a(i), on the basis that the species could have a very small population (perhaps fewer than 2,500 mature individuals, given the paucity of records) which is inferred to be in decline owing to habitat loss and degradation in some areas, with all subpopulations perhaps numbering fewer than 1,000 mature individuals.

R. longirostris (as defined following the taxonomic change) inhabits primary forest, mature secondary growth, dry forest and areas of bamboo, mainly in the lowlands and hills of the Thai-Malay Peninsula, Sumatra and Borneo (del Hoyo et al. 1994, Madge and McGowan 2002). It may warrant listing as Near Threatened under criteria A2c+3c+4c, as it could be undergoing a moderately rapid population decline (approaching 30% over three generations [c.12 years]) owing to on-going habitat loss and degradation.

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

References:

del Hoyo, J., Elliott, A. and Sargatal, J. (1994) Handbook of the birds of the world, Vol 2: New World Vultures to Guineafowl. Barcelona, Spain: Lynx Edicions.

Madge, S. and McGowan, P. (2002) Pheasants, partridges and grouse: including buttonquails, sandgrouse and allies. London: Christopher Helm (Helm Identification Guide).

Mann, C. F. (2008) The Birds of Borneo: An Annotated Checklist. BOU Checklist No 23. Peterborough, UK: British Ornithologists’ Union and British Ornithologists’ Club.

Myers, S. (2009) A field guide to the birds of Borneo. London, UK: New Holland.

Phillipps, Q. and Phillipps, K. (2011) Phillipps’ field guide to the birds of Borneo. Second edition. London, UK: John Beaufoy Publishing.

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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8 Responses to Archived 2014 discussion: Long-billed Partridge (Rhizothera longirostris) is being split: list R. dulitensis as Vulnerable and R. longirostris as Near Threatened?

  1. Simon Mahood says:

    What is the process for arriving at a population estimate and sub-population structure for a species such as R. dulitensis for which there are few (any?) recent records and very few historical records with accurate location data?

    Equally, R. longirostris is extremely patchily distributed, for unknown reasons (as far as I know).

  2. Joe Taylor says:

    Hi Simon,

    Thanks for your post. The preliminary Red List assessment, population estimate and supposed subpopulation structure for R. dulitensis are based on the species’s distribution and range size, relatively recent records and perceived observer coverage. I have adapted the wording of the topic to better express the level of uncertainty in this initial assessment.

    Those with knowledge of the species and region are invited to help improve or correct the assessment and the estimates put forward.

    Joe

  3. Simon Mahood says:

    Hi Joe,

    It’s good to hear that there are relatively recent records of R. dulitensis, I had thought that the species was last recorded in 1937. It is probably no less rare than other poorly known Bornean sub-montane endemics such as Black Oriole and Dulit Frogmouth, although with the caveat that it must be vulnerable to hunting and its closest relative is notoriously patchily distributed. Like those two species it might be largely restricted to Sarawak. Rate of habitat loss within its range is likely to be the most important factor determining its red list status. Is there any evidence that habitat degradation effects either Rhizothera species?

  4. Joe Taylor says:

    It may well be the case that R. dulitensis has not been recorded with certainty since 1937, as noted to be apparent by Orenstein et al. (2010).

    There are records from the second half of the 20th century of a Rhizothera species near Tenom in the Crocker Range, Sabah (J. B. Comber), the identity of which has been regarded as having ‘not been determined precisely’ (Smythies 1999), although they appear to be attributed to R. longirostris by Davison (2008) and regarded as ‘sight records’ of R. dulitensis by Phillipps and Phillipps (2011).

    Initially it seems unlikely that R. dulitensis is still extant in Kinabalu National Park, Sabah, given the lack of records and countless birders who have visited the area since it was collected there in 1895 (Davison 2008, Orenstein et al. 2010); however, it has been pointed out that coverage by birders may be low in areas of the park that are within the species’s known elevation range (900-1,200 m; Smythies 1999), and the species’s call is still unknown (Davison 2008).

    It is not clear how frequently its probable range in Sarawak (known from Gn Dulit, Gn Murud and Gn Batu Song; Smythies 1999) has been covered by anyone potentially looking for this taxon, and coverage is provisionally assumed to be very low. A one-week visit by Ben King in September 2004 did not yield any records of R. dulitensis (www.kingbirdtours.com/news). Further information is requested.

    R. longirostris is listed by Madge and McGowan (2002) as occurring in well-grown secondary forest, dry forest and areas of bamboo (in addition to primary forest), and has been recorded in logged forest (Smythies 1999), suggesting some tolerance of habitat modification. Orenstein et al. (2010) state that R. dulitensis may be under serious threat from habitat degradation and hunting.

    Additional references:

    Davison, G. W. H. (2008) Records of Rhizothera (longirostris) dulitensis in Sabah. Forktail 24: 125-127.

    Orenstein, R., Wong, A., Abghani, N., Bakewell, D., Eaton, J., Yeo Siew Teck and Yong Ding Li (2010) Sarawak – a neglected birding destination in Malaysia. BirdingASIA 13: 30-41.

    Smythies, B. E. (1999) The birds of Borneo. Fourth Edition, revised by Davison, G. W. H. Kota Kinabalu, Malaysia: Natural History Publications (Borneo).

  5. Yong Ding Li says:

    One of the problems faced by many Bornean submontane endemics is that they occur in an (sometimes narrow) elevational band seldom visited by birdwatchers, adding on to inadequacies in assessment of status. Outside of Sabah, the Bornean interior is poorly sampled and so many species that do not have strongholds at the well-birded areas are expectedly little known (e.g. Black oriole, Dulit frogmouth). Dulit Partridge falls into this category, but of course unlike others small passerines, it faces additional pressures from hunting. Given the small geographical range, apparent low density (as inferred from low encounter rates), elevational band and the threat of habitat degradation (increasing logging up slopes across Sarawak) and hunting pressures, it might be prudent to adopt a precautionary stand and designate the species either as vulnerable or endangered.

    Long-billed partridge is similarly a low density species, but more widespread and has a wide elevational band from near sea-level to at least 1300m based on regular records from Fraser’s hill. Some populations seem to persist a long time in fragments, especially that around Kuching and suggest some level of resilience to habitat degradation. For some strange reason the species is very patchily distributed and I have not encountered it in good lowland Dipterocarp forest in places like Taman Negara National Park (Peninsular Malaysia) or the logged Panti Forest Reserve (Peninsular Malaysia). On the other hand, i have encountered it in tiny forest fragments (no more than tens of hectares) in Kuching’s outskirts, as well as in good slope forest at lower elevations of Fraser’s Hill (800m asl)

  6. 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:

    R. longirostris as Least Concern

    R. dulitensis as Vulnerable under criterion C2a(i)

    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.

  7. Yong Ding Li says:

    I think near-threatened/lower risk may still be a more appropriate category for Long-billed Partridge for three reasons:

    1. Densities and abundances are low (for reasons not well understood), based on surveys across suitable habitat in Malaysia, Indonesia and South Thailand.
    2. The species is rare or absent from many areas of good habitat (and definitely more so than similar Sundaic (passerine) species currently listed as near-threatened) – if it is present it should be easily detected given its vocal habits.
    3. The species like most galliforms in the region, remains vulnerable to hunting pressure.

  8. Andy Symes says:

    Recommended categorisations to be put forward to IUCN

    Based on available information and comments posted above, our recommended categorisations to be put forward to IUCN for the 2014 Red List are:

    R. longirostris as Near Threatened – nearly meeting the thresholds for classification as Vulnerable under criterion A2cd+3cd+4cd – change to the preliminary proposal

    R. dulitensis as Vulnerable under criterion C2a(i)

    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.

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