Crested Argus (Rheinardia ocellata): revise global status?

Crested Argus has two subspecies with range as follows (McGowan and Kirwan 2018):

R. o. ocellata – Annamite mountain chain in central and southern Vietnam (south to the Da Lat Plateau) and neighbouring eastern Laos.

R. o. nigrescens – mountains in C Peninsular Malaysia, mainly within Taman Negara National Park.

It is currently classified as Near Threatened on the basis of a moderately rapid population decline (approaching 30%) suspected to be taking place over three generations (16 years). It was argued by N. Brickle and J. C. Eames in litt. (2004) that there was little to suggest that the overall population was in decline, but a moderately rapid decline was maintained on a precautionary basis given the potential of locally high hunting pressure and continuing habitat loss.

There is little information available to calculate the population size, but the current Red List assessment uses a preliminary estimate that the population lies within the band 10,000-19,999 individuals, very roughly equating to 6,000-15,000 mature individuals.

The lack of recent records from the Indochinese part of the range does however suggest that a significant decline may have taken place, and it has been suggested that the species may now warrant listing in a category higher than Near Threatened (R. J. Timmins in litt. 2017).

At the previously reliable site of Bach Ma National Park (Vietnam) it was apparently last heard in 2010 (Radstaak undated). The same report considered that Lo Xo Pass was now “most likely…the only spot to hear this species in Indochina”. Other recent records from Indochina do indeed appear to be few and far between, even allowing for the elusive nature of the species. Automatic recorders detected the species at three sites within Ngoc Linh Nature Reserve (on the border of Kon tum and Quang Nam provinces) in 2016 (Vu Tien Thinh et al. 2017), while in Laos, it was heard at Khoun Xe Nong Ma protected area in 2017 (Mayer 2017). The only record on eBird within the last ten years is apparently of three individuals at Dak Blo Road (Kon Tum) in 2011 (https://ebird.org/view/checklist/S22418325).

The range of subspecies nigrescens is small, although wider than once thought, including the eastern flank of the East Coast Range of Peninsular Malaysia, where it is restricted to a narrow altitudinal band (D. Wells in litt. 2005). Previously it had been known only from eight sites within, or very close to, Taman Negara National Park. Populations on each mountain are likely to be small, and based on past field surveys the total population of this race was estimated at c. 200–2000 individuals; field studies in mid 1970s indicated population density of c. 8 birds/km² in 125–250 km² of habitat (McGowan and Kirwan 2018). Although it appears to be under less immediate threat than the Indochinese population, there is a lack of recent information from the Malaysian range.

Assessment against Red List Criteria

Criterion A – If the overall population was suspected to be decreasing by 30-49% in three generations (18 years) it would warrant listing as Vulnerable under Criterion A. If suspected declines were even higher, exceeding 50% in three generations (18 years) it would warrant listing as Endangered or higher. Declines approaching 30% in three generations would mean the species would continue to warrant listing as Near Threatened under the same criterion. Clearly there is very limited information to calculate trends for this species, therefore a careful analysis of the likely extent and severity of threats to the species across the range should be used to produce a best estimate for the rate of population change.

Criterion B – The species has an extent of occurrence (EOO) of 4,590,000 km2 so it does not meet the threshold for listing as Vulnerable under criterion B1. Please note that this is the area of a minimum convex polygon around the known range, and does not equate to the extent of suitable habitat for the species. The global area of occupancy (AOO) has not been calculated, but given the EOO, the AOO likely exceeds the threshold for Vulnerable under this criterion (2,000km2). Therefore, the species likely does not warrant listing as globally threatened under this criterion.

Criterion C – The global population is currently thought to lie within the range 6,000-15,000 mature individuals, although there is a very high degree of uncertainty about the total population size.  It could warrant listing as Vulnerable under criterion C2a(i) if total population was <10,000 mature individuals with ≤1,000 in each subpopulation, and a continuing population decline was inferred to be taking place (or if the total population was <2,500 mature individuals with 250-1,000 in the largest subpopulation). It would warrant listing as Endangered under criterion C2a(i) if the total global population is estimated to number <2,500 mature individuals with ≤250 in each subpopulation, and an inferred continuing population decline.

Criterion D – The population size and range are too large to warrant listing this species as Vulnerable under this criterion.

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.

The only relevant criteria for the assessment of this species are criteria A and C. The likely rate of population decline, along with potential population (and subpopulation) size are therefore key to determining whether a status change is warranted.

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 information that is sought, or about the species’ Red List status.

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2 Responses to Crested Argus (Rheinardia ocellata): revise global status?

  1. Simon Mahood says:

    Note that the Dak Blo Road and the Lo Xo Pass are different names for the same site.

  2. Yong Ding Li says:

    Small numbers of the nominate subspecies has been documented recently in Khe Nuoc Trong by the survey team from Viet Nature (BirdLife in Vietnam), more details of encounter rates will be made available in upcoming papers. In Peninsular Malaysia, surveys have revealed a small, but potentially significant population of the nigrescens subspecies north-east (and outside the boundary of the Taman Negara), occurring from above 900m asl. More on this population will also be released very shortly. All data were collected using camera traps.

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