Archived 2011-2012 topics: Taxonomic change in the genus Cissa: list Javan Green Magpie (C. thalassina) as Critically Endangered and Bornean Green Magpie (C. jefferyi) as Least Concern?

Initial deadline for comments: 31 January 2012.

BirdLife species factsheet for Short-tailed Magpie (prior to taxonomic change)

Short-tailed Magpie Cissa thalassina has been split into Javan Green Magpie C. thalassina and Bornean Green Magpie C. jefferyi following a study into the vocalisations, morphology and plumage variation of Cissa taxa by van Balen et al. (2011).

C. jefferyi is endemic to the island of Borneo, where it occurs in foothill and montane forest at c.300-2,750 m, although rarely below 1,400 m, and is described as not uncommon in the higher-elevation forests of Mt Kinabalu National Park (del Hoyo et al. 2009, van Balen et al. 2011). It is expected to qualify as Least Concern on the basis that it does not approach the thresholds for Vulnerable under the IUCN criteria. The species’s Extent of Occurrence (EOO) is estimated at c.131,000 km2 (BirdLife International and Natureserve 2011), thus it does not approach the thresholds for Vulnerable under the range size criteria (B and D2: EOO 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 size is probably fairly large given its range, and hence is not thought to approach the thresholds for Vulnerable under the population size criteria (C and D1: 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). Rapid forest clearance in the lowlands of Borneo has probably affected areas of forest at the lower end of the species’s elevation range, thus the population is probably in decline, but it may be relatively secure in high elevation forests in remote parts of the interior of Borneo and occurs in a number of protected areas (van Balen et al. 2011), thus there is no evidence that the rate of decline is moderately rapid (20-29% over three generations, estimated at 20 years; BirdLife International unpubl. data) or more severe, thus it is not thought to approach the threshold for listing as Vulnerable under the population reduction criterion (A: at least a 30% decline over ten years or three generations, whichever is longer).

C. thalassina is endemic to west Java, where it habits mainly foothill and montane forest at 500-2,000 m, occasionally ranging into lowland areas, and may be seen in adjacent cultivated areas and at the edge of forest (van Balen et al. 2011 and references therein). There are few recent records and the species now appears to be very rare and localised.

On Java, most forest below 1,000 m, and in some areas up to 1,500 m, has been cleared, which has no doubt caused serious declines in this species’s population, and excessive trapping for the cage-bird trade is also thought to be a significant threat, although only relatively small numbers have ever been recorded in bird markets (van Balen et al. 2011 and references therein). Bird-catchers tend to specialise in particular species, suggesting that remnant populations are at increased risk of local extirpation through targeted trapping pressure.

It has been recommended by van Balen et al. (2011) that C. thalassina be listed as Critically Endangered on the basis of a past and future decline of at least 80% over ten years (preferably over three generations = 20 years; BirdLife International unpubl. data), based on the paucity of recent records, a fall in numbers seen in bird markets, and rapid rates of habitat loss and fragmentation; and its apparently extremely small population, which could number fewer than 250 mature individuals, with each sub-population probably containing 50 or fewer individuals, and is probably declining, possibly at a rate of 25% or more over one generation (6.7 years; BirdLife International, unpubl. data). It is also said that the total population probably does not exceed 100 individuals and could number fewer than 50 individuals, as there may be only one or two dozen individuals at each of up to four sites where the species has been recorded in the past ten years and may still be extant (van Balen et al. 2011).

It seems that there is little evidence on which to base a suspected population decline of 80% or more over the past and next three generations, despite the likelihood of the species’s population now being extremely small and localised. Although the numbers of birds on sale in markets are said to have decreased markedly (van Balen et al. 2011), more data are required on the rate of habitat loss in the species’s suspected range. In addition, the threat of future habitat destruction is alleviated somewhat by the protected area status of the four locations with records since 2001, including three national parks and one protection forest/nature reserve, although encroachment is occurring along their borders (van Balen et al. 2011). Although there has been a paucity of records in recent years, it may be too pessimistic to estimate a total population of fewer than 50 mature individuals. It is therefore proposed that the species be listed as Critically Endangered under criterion C2a(i) on the basis that the population is likely to number 50-249 mature individuals, in which each sub-population probably numbers 50 or fewer mature individuals, and is inferred to be in continuing decline owing to on-going trapping pressure and habitat loss and degradation.

It should be noted that for the purposes of Red List assessments, sub-populations are defined as geographically or otherwise distinct groups between which there is little or no demographic or genetic exchange, i.e. typically one successful migrant per year or less. Thus it should be indicated if, based on this definition, at least 90% of all mature individuals in the species’s population are likely to form one sub-population.

Comments are invited on the proposals to list C. thalassina as Critically Endangered and C. jefferyi as Least Concern, and further information would be welcomed.

References:

BirdLife International and Natureserve (2011) Bird species distribution maps of the world.

del Hoyo, J., Elliot, A. and Christie, D. A. (2009) Handbook of the Birds of the World, Vol 14. Bush-shrikes to Old World Sparrows. Barcelona, Spain: Lynx Edicions.

van Balen, S., Eaton, J. A. and Rheindt, F. E. (2011) Biology, taxonomy and conservation status of the Short-tailed Green Magpie Cissa [t.] thalassina from Java. Bird Conserv. Int.

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One Response to Archived 2011-2012 topics: Taxonomic change in the genus Cissa: list Javan Green Magpie (C. thalassina) as Critically Endangered and Bornean Green Magpie (C. jefferyi) as Least Concern?

  1. Joe Taylor says:

    The following comment was received from Frank Rheindt on 31 January 2012:

    your summary of the situation is already so good, there isn’t really anything to add beyond what has been said in Van Balen et al. (2012).

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