Data Zone
Justification of Red List category
This iconic duck of South-East Asia's wetlands is on the verge of extinction. A combination of threats including habitat loss, disturbance and hunting have caused a precipitous decline over the past three generations (26 years), probably exceeding 80%. There are now likely only 150-400 mature individuals left, widely scattered in populations across its once vast range, many of which are probably now too small to be viable. The species likely has an extremely high chance of becoming extinct in the near future. It is therefore listed as Critically Endangered.
Population justification
Compiling an accurate global population size estimate for this species is obfuscated by a lack of robust count data from large parts of its range, but evidence of continuing declines from already low numbers (BirdLife International 2001) suggests that the global population size may now be very small. The status in each range state is discussed approximately from west to east / north to south.
India was long-considered this species' stronghold but it is evident that the species occupies considerably fewer sites, and in fewer numbers, than it did three generations ago (BirdLife International 2001, Ahmed et al. 2023). The Indian population was previously estimated to number 300–400 individuals based on surveys in the early 1990s (Choudhury 1996), however is postulated now to be 'far less as the species has lost a significant part of its habitat in the last 25 years' (Ahmed et al. 2023). As evidence, the species has disappeared from several formerly occupied sites (see Figure 2: Ahmed et al. 2023), with no records in recent surveys from, for example, Dibru-Saikhowa National Park and Doomdooma Dangori Reserve Forests, which had 'large populations' of White-winged Duck in the 1990s (Talukdar and Bhattacharjee 1994, Choudhury 1996). Recent surveys found only a total of 24 individual ducks from three forest areas (Ahmed et al. 2023). Rationalising these data into population estimates is difficult in the absence of coordinated counts, but recent observations from even purported strongholds have rarely involved more than 1–2 pairs being seen, and combined with the collapse in the number of sites with recent observations, it is estimated that since counts of the early 1990s, the population in India has declined considerably. The precise number may be uncertain, but the conclusion from the limited evidence above is that the maximum population in India is unlikely to exceed 150 adults. Most plausibly, the Indian population now falls within a band of 50-150 mature individuals.
In Myanmar, data are even more sparse. Nonetheless, recent surveys (2016–2020) found birds persisting along the Chindwin River (and its tributaries) in Sagaing and Kachin, principally at Hukuang and Htamanthi Wildlife Sanctuaries. At Hukuang Valley WS the species remained regularly reported 'on all main streams and oxbow lakes surveyed' (R. Tizard pers. obs., in Chowdhury et al. 2020). Tordoff et al. (2007) suggested that the population of White-winged Ducks here was 'several times greater' than the 10 birds they counted in surveys conducted in 2003–2005, and this is validated by an observation of 19 birds (not all of which, however, were likely to be mature individuals) observed in the Hukaung Valley WS in August 2009 (eBird 2023). The total population in Myanmar is precautionarily estimated at 40–100 mature individuals, accounting for observations of rapid habitat loss and degradation at both wildlife sanctuaries (particularly since 2016: Global Forest Watch 2023) which is likely to have (potentially significantly) reduced numbers since many of these surveys were carried out.
In Thailand, very few wild birds remain. A recent photographed record from Thung Yai Naresuan WS (eBird 2023) indicates that a population probably persists in Thailands remote western forests, but the area of suitable habitat here indicates that this is unlikely to comprise a large population. A recent reintroduction project at Phu Khiao WS is yet to be proven self-sustaining. White-winged Duck is almost certainly extinct in Peninsular Thailand and Peninsular Malaysia. There are no recent records from Viet Nam or Lao PDR, where it is probably extinct (or, if any population does persist, must now be tiny and functionally so) (Timmins et al. in press, eBird 2023).
In Cambodia, the population has declined since a proposed estimate of 100 birds in 2007 (J.C. Eames in litt.) and likely now comprises (potentially far) fewer than 50 mature individuals (S. Mahood in litt. 2023), with no recent records away from Preah Vihear (C. Poole in litt. 2023).
In Indonesia, the population has evidently totally collapsed since BirdLife International (2001) identified 20 then recent (1980–2000) sites on Sumatra, most of which have now been totally denuded of forest. Across the island it is now very rare, with remnant populations confirmed from only Way Kambas National Park (where probably fewer than 20 mature individuals) and the Kampar Peninsula (where similar numbers would probably be an optimistic estimate). There are (few) other localities where the species could still persist (e.g. Berbak National Park); the Sumatran population is estimated here to number 30–60 mature individuals, with the lower estimate of this probably being most accurate. There have been no records from Java for over 50 years (BirdLife International 2001) and here it is assumed extinct.
Combining all these data presents an estimate with considerable uncertainty totalling 165–380 mature individuals, which is rounded to 150–450 here to account for additional uncertainties with the data used, but noting that a population size at the lowest end of this estimate is now probably the most likely.
Trend justification
This species' population is estimated to have declined very rapidly owing to the widespread loss, degradation and disturbance of lowland forest wetland habitats. Remaining populations are small, fragmented and of unknown viability but available data suggest a collapse in both range and abundance over the past three generations (26 years: 1997–2023), including in areas where the extent of suitable habitat hasn't changed, suggesting that this species is particularly prone to fragmentation and stochastic events that are poorly understood. Much of this loss was historical, with the map of all known localities presented in BirdLife International (2001: 413) almost unrecognisable when compared to contemporary distribution maps (cf., e.g., eBird 2023). Nonetheless, recent rapid declines are suspected also. Range states are discussed below approximately west to east / north to south.
In India, a lack of recent data make difficult an attempt to calculate plausible rates of decline, but the previous estimate made in the 1990s that the country hosts 300–400 mature individuals seems unreconcilable with recent observations (see Population Size justification). Here the population is thought to have declined by 50–90% over the past three generations, with an urgent need to work out population numbers at each remaining site, particularly the species' two Indian strongholds: Nameri Forest and Dihing–Patkai (eBird 2023, Ahmed et al. 2023).
In Myanmar, declines since 1997 are even less understood, with most sites identified in BirdLife International (2001) with confirmed records from only pre-1980. Nonetheless, many of these sites probably were occupied three generations ago, with records from this era lacking due to a lack of survey effort. If this is the case, the species has probably declined rapidly too, with almost no suitable habitat away from the country's north. Nonetheless, this assumption is hard to test. More recently, deforestation rates in the species' stronghold in the Hukaung Valley have been high (Hansen et al. 2013, Papworth et al. 2017, Global Forest Watch 2023) and declines are assumed to be continuing, despite this region's critical importance.
In Thailand, White-winged Duck had already declined considerably by the late 1990s, but even then persisted locally in Peninsular Thailand, and at Phu Kradung and Nam Nao National Parks, and (naturally) at Phu Khieo Wildlife Sanctuary. It has since disappeared from these three areas, although a reintroduction project at the last-named has begun. Rates of decline over the past three generations are difficult to determine in Thailand; they are likely to have been steep (>70%) but involving a low number of individuals. In Lao PDR has declined rapidly, probably to extinction, in the past three generations. In the late 1990s White-winged Duck was still known to occur on the Nakai Plateau and in the Xe Kong/Bolaven Plateau region (albeit in small numbers), as well as Dong Kanthung (Duckworth et al. 1999). Evans et al. (1997) estimated population sizes of 6–24 adults on the Nakai Plateau and 15–45 in Champasak and Attapu provinces, suggesting a total population of 21-69 mature individuals at that time. The species is now probably extirpated in Lao PDR, or has a population so small that it is unlikely to be functional (Timmins et al. in press). In Cambodia the population size in the 1990s is poorly known, but up to 2007 the country was thought to host up to 100 birds (J. Eames in litt. 2007). The population has declined rapidly since then (estimated here at 50–90%) and likely now comprises (potentially far) fewer than 50 mature individuals (S. Mahood in litt. 2023), with no recent records away from Preah Vihear (C. Poole in litt. 2023). In Viet Nam, has probably been extirpated within in the last three generations although even by the 1990s it was known from only Cat Tien National Park, where birds reportedly persisted until 2005; there have been no more recent records (eBird 2023).
In Indonesia, declines have evidently also been very rapid. BirdLife International (2001) estimated then that Sumatra hosted 150, but it is probable that this was an underestimate (certainly if 150 mature individuals was correct, it indicates a then island-wide density considerably lower than that in suitable habitat observed now). Although it is difficult to backcast population sizes, it is possible that up until the 1990s, the island hosted 2–3 times this number given the area of undisturbed lowland forest still present at that time, of which more >85% has since been cleared (Global Forest Watch 2023). There are no recent records made (or areas of suitable habitat) on the western side of the island, where BirdLife International (2001) identified several occupied localities. The species likely went extinct on Java more than 50 years ago (BirdLife International 2001).
In the counterfactual scenarios used here, the global population size of this species three generations ago is suspected of having been c.800–1,400 mature individuals, with declines over the same period calculated as approximately 40–90%. This previous population size estimate is similar to those made previously, but may in fact be overly pessimistic for the abundance of the species at that time. For example, Evans et al. (1997) thought the global population was probably 'a few thousand', while Callaghan et al. (1998) thought the non-Indonesian population alone numbered 1,000–5,000 birds. Consequently, while rates of declines over the past three generations are thought to lie within the band of 40–90%, the best estimate is placed at the top end of this band (70–90%), to reflect the very high likelihood that the population size (and range) of this species has collapsed over the past two decades.
Future rates of decline are highly uncertain, but it is apparent that protected areas alone are not sufficient in preventing localised extinctions of this species, which may be highly susceptible to fragmentation as well as threats that can permeate ineffective or poorly managed protected areas. Declines in all parts of its range are thought to be ongoing, so it is difficult to imagine how they may slow in the future. Certainly, if future rates of decline match those over the past 20 years, the species will soon be on the precipice of extinction. Rates of continuing decline are therefore set at the same rates of past ones (i.e. 40–90%, with a best estimate of 70–90%).
Historically, Asarcornis scutulata had a large range that extended through much of eastern South Asia, almost all of South-East Asia, and parts of the western Indonesian archipelago. In many of these range states, the species is now probably extinct, or nearly so. The species still occurs in India (Assam and Arunachal Pradesh), but it is probably now extinct in Bangladesh and was likely only ever a marginal visitor to Bhutan (Choudhury 2007). Occurs in northern Myanmar, which is probably now a stronghold for the species (Tordoff et al. 2007, Chowdhury et al. 2020) and, very locally, still in western Thailand. In the latter, a reintroduced population (which is not yet known to be self-sustaining) is at Phu Khieo Wildlife Sanctuary (eBird 2023). Almost certainly extinct in Peninsular Thailand and Peninsular Malaysia. The species is probably now extinct in Lao PDR and Viet Nam (Timmins et al. in press) or any population that does persist is likely to be so small that it is probably not viable. The population in Cambodia is now greatly diminished with recent reports from only Preah Vihear (C. Poole in litt. 2023, eBird 2023). In Indonesia, remnant and fragmented populations remain on Sumatra, but it is probably extinct through much of the island, as it is on Java.
Usually found alone or in small groups, the species is most easy to see at dawn and dusk when moving between daytime roosts and the species' feeding sites (Green 1993a, Green et al. 2005). It inhabits stagnant or slow-flowing natural and artificial wetlands, within or adjacent to evergreen, deciduous or swamp forests, on which it depends for roosting and nesting, usually in tree-holes. Although lowlands (below c.400 m) provide optimum habitat, it occurs up to 1,400 m, especially on plateaux supporting sluggish perennial rivers and pools. It has been described as omnivorous (Green et al. 2005), with pondweed, small fish, aquatic snails, spiders and insects being consumed regularly (Green 1993a). Breeding season may vary across its range so that hatching coincides with the early wet season, when food supply may be more favourable (Green et al. 2005). The clutch size can vary to quite an extent with a range of 6-13 in captivity and 2-12 in the wild (Mackenzie and Kear 1976, Green 1993a, Green et al. 2005).
The rapid decline of this once widespread species is largely attributable to the destruction, degradation and disturbance of riverine (e.g. wetland drainage [Green 1993b]) and forest habitats that this species is dependent on, including the inappropriate management of forests (e.g. forest burning during the dry season [see Green 1993b]). It may be particularly susceptible to loss of large trees with nesting holes (W. Duckworth in litt. 2006). The resultant small, fragmented populations are vulnerable to extinction from stochastic environmental events, loss of genetic variability, disturbance, hunting and collection of eggs and chicks for food or pets. While trade may be more of a local threat to the species, off-take for hunting, which goes relatively unreported, is a far more serious issue (Green 1993b). The extent to which these threats have affected it in different parts of its range varies. For example, hunting and nest robbery were identified as probably the only threats to have driven the species extinct in Lao PDR (Timmins et al. in press), while on Sumatra the almost total clearance of flat, low-lying forests (Global Forest Watch 2023) for conversion to oil-palm (and to a lesser extent rubber) plantations (Descals et al. 2021, Wang et al. 2023) will likely have been the principal driver of rapid declines there, as well as probably the extirpations in Peninsular Malaysia and on Java. In Myanmar, hunting, disturbance and habitat loss have likely caused rapid declines historically, and probably continue to do so. In particular, in the species' stronghold in the Hukaung Valley, rates of forest loss have been very high and the proliferation of gold-mining is now a well-established threat. (Hansen et al. 2013, Papworth et al. 2017, Global Forest Watch 2023).
The most comprehensive assessment of current threats comes from north-east India, where a significant minority of the world's remaining population remains. Here, Ahmed et al. (2023) identified habitat degradation as a key threat, driven by oil extraction industries, the siltation of wetlands, proliferation of unnamed weed species and wetland draining. Moreover, forest loss caused by illegal logging and encroachment was identified as a threat, although in this region it is probably less so than in other parts of the species' range. Disturbance is a key issue throughout the species' range, and in India is chiefly caused by unregulated tourism, and non-timber resources extraction from forests. Hunting, including nest robbery, is a threat in north-east India as well as elsewhere.
The impacts of climate change are poorly understood (Ahmed et al. 2023 identified this as a key knowledge gap), but a preliminary study concentrating only on the north-east Indian population (Deka et al. 2022) projected minor losses of habitat by 2050.
Conservation Actions Underway
CITES Appendix I. Legally protected in most range states; for example, in India it is listed in Schedule 1 of the Wildlife (Protection) Act. Almost the entire global population now resides in a greatly fragmented protected area network (this study, eBird 2024, UNEP-WCMC and IUCN 2024); in some instances protected area designations were made almost exclusively to safeguard populations of this species (e.g. Dibru-Saikhowa National Park and Dihing-Patkai Wildlife Sanctuary, both in Assam; A. Choudhury in litt. 2016). In Assam, a species action plan was published in 2023 (Ahmed et al. 2023) and a species-recovery project organised by Wildlife Trust India is underway.
In order to establish a captive-breeding population, the Wildfowl and Wetlands Trust (WWT) at Slimbridge, UK received 10 White-winged Ducks from Thailand in 1955, with the intention of breeding them (Green 1993b); however, none reproduced and the last bird died in 1961 (with most dying from avian tuberculosis, to which captive populations of this species seem to be particularly susceptible; Foote 2023). The current captive population in Europe and North America originates from 10 birds (seven males, three females) collected in Assam (India) in 1969-1970, all of which were probably closely related (Foote 2023). The captive population of White-winged Ducks was impressively increased to c. 200 in 2000, but has since declined precipitously to fewer than 25 in 2022 (Figure 1.2, in Foote 2023) and will likely be extinct by 2027 (Foote 2023). The captive population held in Europe is faring better, but remains comparatively small (vs other wildfowl species). A conservation programme led by EAZA supported by the European Union LIFE NGO funding programme currently focuses on ex-situ conservation (EAZA 2024); in July 2023 it was recorded that the programme had 76 White-winged Ducks across 23 institutions in Europe. Other captive populations are held by other institutions and private hobbyists globally, including in South-East Asia (A. Berryman pers. obs.). From an unknown source, some birds were recently reintroduced to Phu Khieo Wildlife Sanctuary, Thailand, where they are regularly seen (eBird 2024); however, the size of this reintroduced population, or whether it is truly sustainable given the species was extirpated from the site some time during the 1990s, is unknown.
Conservation Actions Proposed
Conservation actions must be urgently addressed. Ahmed et al. (2023) produced a blueprint for recovery of the species in Assam, but with suggestions that would almost certainly benefit the species throughout its range. First, they recommend that existing protected areas are strengthened by increasing enforcement and engaging local communities. Second they suggest that areas of suitable habitat in non-protected forests are established, with the aim of establishing these as protected areas (or OECMs) that are effective at safeguarding populations of White-winged Duck. Existing habitat should be restored by the de-siltation and weeding of forest wetlands, as well as the avoidance of contamination from oil drilling, and new habitat could be created via reforestation efforts and wetland creation; it should be noted however, that the latter will likely take time to be effective. Third, they recommend strengthening existing legislation and improving enforcement to prevent hunting and the poaching of eggs; this should be done in parallel with community engagement to discourage accidental and intentional offtake. Fourth, disturbance by local people and by tourists should be mitigated by identifying nesting/feeding areas to local people and staff so that they can be avoided. Investigate whether Assam could and should develop a captive-breeding programme and establish a captive-breeding centre. Fifth, research aimed at determining local attitudes to the species should be carried out, as well as determining which livelihood practices are currently affecting the species; this could be coupled with awareness-raising campaigns to educate local people how these practices can be carried out in less damaging way.
Similar conservation action blueprints should be drawn for the species elsewhere in its range, particularly in Myanmar, Cambodia and Indonesia, where the only remaining viable populations persist. The reintroduction project in Thailand should be reviewed and, if deemed successful, could be replicated in areas where threats are thought to have been adequately addressed.
66-81 cm. Large, dark, forest duck with contrasting whitish head and upper neck. Males have mostly dull yellowish bill, blackish mottling on head and upper neck, white lesser and median coverts and inner edges of tertials and bluish-grey secondaries. In flight, white wing-coverts contrast with the rest of the wings. Females are smaller and usually have more densely mottled head and upper neck. Juvenile is duller and browner. Similar spp. Female Comb Duck Sarkidornis melanotos has mostly whitish underparts and all dark wings. Voice Flight call is series of vibrant honks, often ending with nasal whistle. Also single, short, harsh honks. Hints Very secretive, often feeds only at night.
Text account compilers
Berryman, A.
Contributors
Choudhury, A.U., Duckworth, W., Eames, J.C., Mahood, S., Rahmani, A., Yahya, H., Green, A.J., Sanjaya, A., Allinson, T, Benstead, P., Westrip, J.R.S., Bird, J., Taylor, J. & Poole, C.
Recommended citation
BirdLife International (2024) Species factsheet: White-winged Duck Asarcornis scutulata. Downloaded from
https://datazone.birdlife.org/species/factsheet/white-winged-duck-asarcornis-scutulata on 19/12/2024.
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 19/12/2024.