Current view: Data table and detailed info
Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 1: Non-passerines. Lynx Edicions BirdLife International, Barcelona, Spain and Cambridge, UK.
IUCN Red List criteria met and history
Red List criteria met
Red List history
| Migratory status |
not a migrant |
Forest dependency |
medium |
| Land-mass type |
continent
shelf island
|
Average mass |
4,651 g |
Population justification: A total population of 5,000 individuals was previously estimated by Hancock (1992), Choudhury (2000) and BirdLife International (2001). However, more extensive survey effort in recent years has led to the upward revision of some national totals. Uncertainty is presented by the ratio of birds:mature individuals, with sub-adult non-breeders accounting for a significant percentage of numbers at some sites. In the Indian Subcontinent, the total number of breeding pairs is broadly unknown, but previous estimates of 1,200 mature individuals in India are likely to have underestimated its abundance. Across the Subcontinent in total (mostly India and Nepal), the number of mature individuals is suspected to lie between 2,000 and 5,000, although even these figures may prove underestimates with, for example, a recent survey in Nepal finding 109 nesting colonies (at least 346 nests) across 18 districts (Katuwal et al. 2023). In Myanmar, populations in the south have recently declined, with no more than 250-400 suspected nearly a decade ago (Zöckler et al. 2014), with a figure between 100-400 estimated here. In Continental South-East Asia, the vast majority of the population is hosted in Cambodia, with small numbers (<50 pairs) in Thailand, and perhaps c. 300 in Malaysia. In Cambodia, Goes (2013) estimated as many as 1,500 breeding pairs. Since these estimates were made, the population at Tonle Sap has increased (to c. 500 breeding pairs in 2021: Timmins et al. in prep.) while populations in the north have evidently continued to decline (S. Mahood in litt. 2023). The total number of mature individuals in Cambodia is here set to 1,000-2,500. In Malaysia, a population of c. 300 has previously been suggested (BirdLife International 2001). On Sumatra, the population is very poorly known, but is likely now smaller than the c. 2000 individuals estimated in 1993. On Borneo and Java, no estimations of population size have been made, although the former still contains enough habitat to potentially saw multiple thousands of birds. Combining these data and the uncertainty surrounding them, the global population is estimated to be at least 5,000 mature individuals, but could number as many as 15,000. It is noted that the total number of birds is likely much greater than this, when sub-adult birds are included too.
Trend justification: This species' population is known to have declined rapidly over the past 100 years, in line with increasing levels of felling of colony nest trees, drainage and conversion of wetland feeding areas, agricultural intensification, pesticide use, disturbance and large-scale development in coastal areas, and, in some places most seriously, the persistent and unregulated harvesting of eggs and chicks from colonies. Confounding the elucidation of these trends, however, is a paucity of research from some regions, including those that may now host the most globally significant numbers.
For assessment against Criterion A2, the trend of this species must be considered over the past three generations (41 years: 1982-2023). A discussion for each part of the species' range over this time period follows, broadly from west to east/north to south:
Undoubtedly the species' trend is most favourable in the Indian Subcontinent, where it remains locally common and relatively widespread in open agricultural, as well as forested, landscapes. Few robust data exist but comparing descriptive accounts of abundance and distribution in BirdLife International (2001) with recent citizen science data (eBird 2023) finds little evidence for noticeable declines in number or range extent. Nonetheless, in parts of Assam some breeding colonies have been lost (A. Choudhury in litt. 2023).
The situation in Sri Lanka is poorly known, although nationally it was recently listed as Endangered B2ab(iii) suggesting evidence for a decline in suitable habitat but not necessarily mature individuals (Ministry of Environment, Sri Lanka 2021). In Nepal, in at least some protected areas the number of breeding individuals appears to be stable (e.g. Chitwan National Park: Poudyal and Nepal 2010, Bhattarai et al. 2021), although success rates are influenced, at least locally, by habitat availability in any given year/at any given site (Sundar et al. 2016, 2019). Other populations in Nepal appear to have declined. For example the country's east, Karki and Thapa (2013) reported a decline at Urlabari Forest Grove from 62 adult birds in 2004 (Baral 2005) to 40 in 2013 (Karki and Thapa 2013). Because this is a long-lived species, it is possible that even in areas of its range where its trend appears stable, there are extinction debt effects associated with breeding success that is so far going undetected—this should be closely monitored. Similarly, there is evidence for contracting wetland and breeding habitat extent (Karki and Thapa 2013), with the protection of these considered critical for persistence (Katuwal et al. 2022).
Rapid declines in Bangladesh and Myanmar are largely thought to have predated the time window under consideration here, with populations evidently much-depleted by the 1980s, despite the species having once been common in both countries (BirdLife International 2001). A resident population is likely breeding in the Sundarbans (Chowdhury 2020) and a colony was relatively recently discovered in northern Bangladesh (Chowdhury and Sourav 2012) although these populations combined are probably small and are unlikely to be contributing greatly to the species' global trend. In Myanmar, recent records are from only the northern part of the country and notwithstanding the preceding comments, a recent decline along the Ayeyarwady is evident (Zöckler et al. 2020, C. Zöckler in litt. 2023).
Elsewhere in continental South-East Asia, the population trend of this species is characterised by a steep decline to at least the 1990s (Wells 1999, BirdLife International 2001), followed by a recent resurgence in some areas driven wholly by the protection of Tonle Sap breeding colonies. In Thailand, it has almost disappeared, although this comment was also true more than two decades previously (BirdLife International 2001). Small numbers persist in Phang-Nga on Koh Phra Tong Island (c.30 pairs: K. Webb in litt. 2018) and wanderers from neighbouring Cambodia may be expected to increase in number over the next three generations. Almost identical comments are true of Lao PDR, where recent records are all assumed to refer to wanderers from Cambodia. At the latter, concerted conservation action since the early 2000s to protect the globally important breeding waterbird colonies at Tonle Sap has begun to reverse the precipitous declines of the last century. At Prek Toal, approximately c. 500 pairs bred in 2021 (Timmins et al. in press), representing a significant increase since, e.g., 2002, when only 71 pairs were breeding (Goes 2014). These increases, however, have been at least partially countered in Cambodia by declines outside of the Prek Toal population. Here, there is considerable uncertainty presented by the fact that birds are sparsely distributed through dry and semi-evergreen forest (S. Mahood in litt. 2023) but between 2009 and 2017 (mostly post-2014), the number of nesting Lesser Adjutants in the Northern Plains forests declined by 60% (from >250 nests to <100), principally due to the loss of and disturbance to nesting habitat.
In the Sundaic region, few empirical data are available. Numbers in the Matang Mangrove Forest, Malaysia, remained relatively constant for 20 years to 2006 (Li et al. 2007) and numbers over the past five years, at least, appear stable along the western coast of Malaysia (eBird 2023). Nonetheless, few colonies are known (J. Eaton pers. comm.), and the long-term viability of these populations is unknown. Alternatively, population trend data from Sumatra suggest a rapid reduction over the past three generations. Estimates in South Sumatra and Jambi provinces in 1984-1986 were 514 birds (388-620) and 272 (152-475) birds respectively, while surveys in these provinces in 2001-2004 estimated only 124 birds (30-318) and 7 birds (2-17) respectively (M. Iqbal in litt. 2013). There is no indication of recovery over the past decade with numbers in both provinces evidently remaining low (eBird 2023). The species is thinly spread throughout the rest of Sumatra, with recent records throughout central and northern provinces only rarely consisting of more than 1-2 birds, with a slightly larger population probably persisting in Way Kambas (eBird 2023). Trend data from Borneo are almost non-existence, but the near-catastrophic removal of lowland forest over the past three generations (Global Forest Watch 2023) is assumed to have removed colonies from across the island which may, at one time, have hosted a significant portion of the global population.
Combining trends from across this species' global range is difficult owing to incomplete data, and great uncertainty about past population sizes and current trends. In South Asia, the population is broadly suspected to be stable or decreasing only very slowly. In continental South-East Asia, the population has certainly declined since the 1980s, but is now likely increasing despite local declines. In the Greater Sundas, the population is almost certainly still declining, potentially rapidly, in response to forest loss, predation and disturbance of nesting colonies. Combining these trends with approximations for population sizes in each region, the global population is suspected to have declined by 10-40% over the past three generations, with a best estimate lying somewhere between 15 and 29%. More empirical data, and ongoing monitoring of populations in South Asia, especially, are urgently sought however. The trend over the next three generations is unknown, but as long as conservation programmes continue to protect colonies in Cambodia, and in South Asia protected areas continue to refuge breeding colonies from disturbance, there is hope that the species' global population will remain stable or slowly increase. This may also be reflected by the re-colonisation of countries from which it has effectively been extirpated, including much of Thailand and Lao PDR.
Country/territory distribution
Important Bird and Biodiversity Areas (IBA)
Recommended citation
BirdLife International (2024) Species factsheet: Lesser Adjutant Leptoptilos javanicus. Downloaded from
https://datazone.birdlife.org/species/factsheet/lesser-adjutant-leptoptilos-javanicus on 18/12/2024.
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 18/12/2024.
