Data Zone
Justification of Red List category
This forest partridge is at risk from a rapid future reduction in the area of its cool mid-elevation eastern Himalayan habitat due to climate-driven changes. Bioclimatic envelope modelling predicts a reduction in the total area of suitable habitat of nearly 40% by 2070, indicating that rates of reduction are likely to exceed 20% over the next three generations. This is separate from current low estimated rates of forest loss and some localised hunting suspected of causing a current decline in the species' population. Accordingly, the species is assessed as Near Threatened.
Improved information on the distribution of the species strongly indicates that the global population size is unlikely to approach threatened thresholds. Therefore, although the ongoing slow loss of forest cover and localised high hunting pressure may be causing a decline, the species does not qualify as threatened under the small population size and decline criterion. Equally, while the area and likely quality of habitat is inferred to be declining, the species does not approach thresholds under the small range and decline criterion.
Population justification
A previous population size (BirdLife International 2016) is considered to have been an underestimate. The species has been modelled as having an area of suitable habitat between 66,000 and 80,000 km2 (Bagaria et al. 2021), and where dedicated fieldwork has been carried out within this area the species is typically present (although unobtrusive). An investigation into the species in Thrumshingla National Park, Bhutan, provided density estimates of 1.67 (1.27-2.17) individuals per square kilometer based on calling birds (Dhendup 2015), equivalent to a population size of between 80,000-140,000 mature individuals. Consequently, it appears most plausible that the population currently exceeds thresholds for listing as threatened under the population size criterion.
However, this highly-forest dependent species (primarily responding to the presence of dense bamboo rather than canopy cover) has suffered from a low but continuing rate of forest cover loss from within its mapped range over the past three generations, and is known to additionally suffer from high hunting pressure in at least parts of the range such as the Mishmi Hills. In combination, these threats are suspected to be causing a decline in mature individuals, as the population size is considered to be directly related to habitat area and also to be reduced by hunting. But the impact of climate on the future extent of the species's habitat may cause an acceleration in the rate of population reduction: bioclimatic envelope modelling predicts that of current suitable habitat, 47% will become unsuitable by 2070 while only an additional 8% will become newly suitable (Bagaria et al. 2021). If these changes are already occurring, this would be the equivalent of a linear rate of loss of 21% over the next three generations, with any impacts from other threats additional to this.
Trend justification
The species is suspected to have been declining at a slow rate in the recent past, owing to on-going forest conversion driven by a slowly expanding human population within its range coupled with high hunting pressure in parts of the range. Significant measures have been taken to safeguard forests in Arunachal Pradesh and Bhutan, lending hope that suitable habitat can be conserved. However, the species is predicted to be one of the galliformes that is most severely impacted by climate change (Bagaria et al. 2021), which may see an acceleration of the rate of population reduction. Bioclimatic envelope modelling predicts that 47% of current suitable habitat will become unsuitable by 2070, offset by an increase of only 8% becoming newly suitable (Bagaria et al. 2021). Assuming a direct relationship between area of suitable habitat and population size, a net area change of -39% between 2021 and 2070 would be expected to result in a linear rate of population reduction equivalent to 21% over the three-generation period between 2021 and 2035, while an exponential rate of population reduction would be equivalent to 32% over the same period. The former is the more plausible shape of the projected reduction given the threat (which may manifest as an accelerating impact), hence the rate of reduction over the next three generations due to this threat is suspected not to exceed 21%. The uncertainty around this prediction may be large but is not quantified: the individual species model for the bioclimatic envelope modelling performed relatively poorly but the ensemble model (with several galliform species with similar habitat requirements included) performed well, but missed a significant extent of this particular species's postulated occurrence (supplementary information in Bagaria et al. 2021).
Forest loss due to conversion for agriculture is considered most likely to continue at a similar rate as most recently estimated: a maximum three-generation equivalent of 2.4% (data from Global Forest Watch 2021, using Hansen et al. [2013] data and methods disclosed therein). It is unclear how this loss will interact with changes predicted due to a shifted climatic envelope. The impact of hunting on the species may be significant in small pockets of the range: in the Mishmi Hills hunting pressure has been reported to be severe but there are large parts of the range that are largely undisturbed, as well as a significant proportion of the range being within protected areas. The impact of hunting is therefore unlikely to have a significant impact on the total population.
Overall, past rates of population reduction are suspected to have been in the range 1-9% over three generations, while the predictions from the bioclimatic envelope model suggest that a best value for a future reduction is 21%, although within a wide band, here given as 10-29%. A rate of reduction that includes the present will be fastest for the period which extends furthest into the future, between 2020 and 2034, and is placed in the band 10-25%, but is still predicted to be just above 20% over this period.
Arborophila mandellii is endemic to the eastern Himalayas north of the Brahmaputra, and is known from Bhutan, West Bengal (Darjeeling only), Sikkim and Arunachal Pradesh in north-eastern India, northern Myanmar , south-eastern Tibet, China (MacKinnon and Phillipps 2000, Spierenburg 2005, Zhang et al. 2017, McGowan et al. 2020, Naing et al. 2020, eBird 2021, GBIF 2021). There are recent records spread throughout Bhutan. It is locally common in the remaining forests of Arunachal Pradesh and perhaps also in parts of West Bengal, suggesting it may be evenly distributed right across its range, wherever suitable habitat occurs. While there are records from the low hills (c. 250 m) in the Bhutan duars, most records are from mid-elevations and above 1,000 m, at least in Bhutan (Spierenburg 2005, Dhendup 2015).
A species distribution model has been derived for this species as part of a species-group of galliformes associated with high-density vegetation in the eastern Himalayas (Bagaria et al. 2021). This cohort was predicted to have between 66,044 km2 (using bioclimatic envelope models) and 79,852 km2 (using the species distribution models) (Bagaria et al. 2021). Within India, the occupied range has been estimated as 13,833 km2 (State of India's Birds 2020). From these values, while they have not been calculated at the correct scale to be considered a valid Area of Occupancy (AOO: IUCN 2022), it is very likely that an AOO would considerably exceed the thresholds for listing as threatened under the range size criterion. The Extent of Occurrence (EOO: IUCN 2022), a minimum convex polygon around mapped confirmed and probable occurrence polygons based upon multiple sources (Rasmussen and Anderton 2012, Dunn et al. 2016, Zhang et al. 2017, Naing et al. 2020, eBird 2021, GBIF.org 2021), is estimated at 227,000 km2. The species is highly dependent upon forest habitats, and within the mapped range forest cover loss has proceeded at a slow rate, up to 2.4% over the past three generations (data from Global Forest Watch 2021, using Hansen et al. [2013] data and methods disclosed therein). This suggests that there is a continuing decline occurring in the area, extent and also likely in the quality of the species's habitat.
Bagaria et al. (2021) used their modelled distributions and future climate predictions to predict that this species would be among the Himalayan galliformes most severely impacted by climate change. Under the RCP 4.5 scenario, 47% of currently suitable habitat was predicted to become unsuitable by 2070, while only 8% would become newly suitable (Bagaria et al. 2021). As such, the rate of habitat loss is suspected to accelerate over the next three generations, and is likely to cause a reduction in the EOO and AOO as well as exacerbating the declines in habitat quality.
The species is resident in the undergrowth of evergreen forest, including bamboo, often close to streams, from perhaps as low as 350 m up to 2,500 m, but in Bhutan recent records are only between at 1,000-2,100 m (Spierenburg 2005, Dhendup 2015). In Bhutan, its known distribution is almost entirely confined to areas with extensive old-growth forest suggesting that the species may be sensitive to habitat degradation (P. Spierenburg in litt. 2004). Calling birds are heard from mid-March to June (Spierenburg 2005).
Bioclimatic envelope models predict the net loss of 39% of the species's habitat, in eastern Himalayan temperate forest with dense understorey (particularly bamboo), due to shifts caused by climate-change under the RCP 4.5 scenario by 2070 (Bagaria et al. 2021). It is unclear whether there is any mitigation or action that can offset this change, beyond preventing additional habitat loss to other drivers. Forest degradation and fragmentation as a result of shifting cultivation, timber harvesting and clearance for tea plantations has affected a small part of the range of the species and is continuing. The species is highly associated with old-growth forest (Spierenburg 2005) and the rate of forest cover loss across the range has been 2.4% over the past three generations (data from Global Forest Watch 2021, using Hansen et al. [2013] data and methods disclosed therein). Beyond this the species may be impacted by fragmentation effects, but potentially unsustainable collection of bamboo or clearance of dense undergrowth may be impacting a larger proportion of the species's range than that showing direct forest loss. Singalila National Park suffers high incursion rates from visitors coming to hunt, collect forest products and graze livestock. Extensive grazing across much of its range is a further threat. As Bhutan's population increases, shifting agriculture and grazing are likely to become problems within the species's altitudinal range, despite the country's admirable forestry policy (Spierenburg 2005). It is suspected that snares set primarily for mammals may also capture a small number of this species: galliformes are frequently captured in this way.
Hunting in the Mishmi Hills (including within protected areas) is apparently severe, although there does not appear to have been a direct record of this species being trapped (Aiyadurai 2012). Interviews in communities surrounding Thrumshingla National Park in Bhutan reported the suspicion of poaching of the species taking place in the National Park (Dhendup 2015). Further infrastructure projects, such as hydroelectric schemes may have caused an increase in trapping and hunting pressure and facilitated illegal logging in addition to direct impacts on habitat through the development footprint and associated infrastructure (A. Rahmani in litt. 2012).
Conservation Actions Underway
It is known from a number of protected areas: Singhalila National Park, Neora Valley National Park and Buxa Tiger Reserve in West Bengal; Maenam WLS (A. Rahmani in litt. 2012) in Sikkim (but there do not appear to be any recent records here [Acharya and Vijayan 2010]); Namdapha National Park, Mehao, Eaglenest and Dibang Valley Wildlife Sanctuaries in Arunachal Pradesh (Choudhury 2008, A. Rahmani in litt. 2012, eBird 2021, GBIF.org 2021); and Nameri National Park and Subansiri Reserve Forest in Assam (Choudhury 2000, A. Rahmani in litt. 2012). It is found in several protected areas in Bhutan, including Jigme Singye Wangchuck National Park, Thrumshing La National Park, Jigme Dorji National Park and Jomotsangkha Wildlife Sanctuary (Inskipp et al. 2000, BirdLife International 2001, eBird 2021, GBIF.org 2021).
A recent ban has been placed on timber export from forests in Arunachal Pradesh. Bhutan's national policy to maintain forests over 60% of the country potentially goes a long way to ensuring a safe long-term future for this species there, and c. 35% of the country is designated as a Protected Area (26%) or Biological Corridor (9%) (P. Spierenburg in litt. 2004).
28 cm. Distinctive partridge with chestnut breast-band and grey belly. Similar spp. Distinguished from similar Rufous-throated Partridge A. rufogularis by more rufescent crown and head-sides, white gorget and entirely chestnut upper breast. Voice Repeated loud prrreet, followed by series of prr prr-er-it phrases, ascending to climax.
Text account compilers
Berryman, A., Martin, R.
Contributors
Benstead, P., Bird, J., Davidson, P., Ghose, D., Inskipp, C., Keane, A., Rahmani, A., Spierenburg, P. & Taylor, J.
Recommended citation
BirdLife International (2024) Species factsheet: Chestnut-breasted Partridge Arborophila mandellii. Downloaded from
https://datazone.birdlife.org/species/factsheet/chestnut-breasted-partridge-arborophila-mandellii on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.