Data Zone
Justification of Red List category
Icthyophaga humilis is listed as Near Threatened. There is little known about the population size of this species, but the loss of riverine forests and the cumulative impacts of overfishing and pollution have led to ongoing declines in the population. Although the species has shown some ability to adapt to alternative and sub-optimal habitat in southern India and Indonesia, the population is suspected to have undergone a reduction of 20-29%.
Population justification
The global population size of Icthyophaga humilis is unknown. In optimal habitat, one pair may occupy every 3-5 km of fast flowing river, however the species is thought to be declining across its contracting range (Praveen 2011, Karuthedathu 2023). The species is considered rare and local in Nepal, Bhutan, and across the Indian Subcontinent (Rasmussen and Anderton 2012, Karuthedathu 2023). It is scarce and localised in Thailand, Vietnam, Cambodia, and Lao PDR (Fuchs et al. 2007, Goes 2013, Treesucon and Limparungpatthanakij 2018, CBGA 2019, Karuthedathu 2023). In Cambodia, five different breeding pairs were recorded along the Mekong in in Northern Kratie region in 2007 (Bezuijen et al. 2008), but none were seen along when the same region was revisited in 2018 (Mittermeier et al. 2019), suggesting a decline in the Mekong river population. The species is highly localised in Lao PDR, but it may represent one of the most significant populations in South-East Asia, with an estimated 20 pairs within Phou Den National Protected Area alone (Fuchs et al. 2007). However, the species reportedly occurs in higher abundance in the Hakaung Valley in northern Myanmar (Fuchs et al. 2007). In Myanmar, the population is still considered unlikely to exceed 1,000 birds due to the continued impacts of deforestation, and other human impacts (Ferguson-Lees and Christie 2001), although this may be pessimistic. The species occurs in Hainan, but is naturally very rare and is potentially only a winter visitor (MacKinnon and Phillipps 2000, Shing et al. 2007 Lewthwaite et al. 2021). Overall, the Indochinese population is thought to only be in the low hundreds due to the paucity of suitable forested river systems (Bezuijen et al. 2008). There is little known about the distribution and population in Malaysia and Indonesia, but it similarly appears to be uncommon and localised (Mann 2008, Puan et al. 2020, Eaton et al. 2021, eBird 2024). It is reportedly scarce in Peninsular Malaysia, uncommon in Sumatra and Borneo, and uncommon to rare on Sulawesi (Karuthedathu 2023).
The population is undoubtedly restricted despite the wide range of the species. However, there is insufficient information on the population size across much of the species' range. Therefore, it is not possible to provide an estimate of the population size.
Trend justification
Icthyophaga humilis is thought to be declining across most of its range caused by a combination of habitat loss, siltation, overfishing, hunting, and increasing human disturbance of waterways (BirdLife International 2001, Ferguson-Lees and Christie 2001, Karuthedathu 2023).
There are apparent declines in the Cambodian population. Three surveys carried out throughout 2007 along 130 km of riverine and floodplain habitat along the Mekong Rover found five different breeding pairs (Bezuijen et al. 2008), but the species was not recorded when the same region was revisited 10-years later (Mittermeier et al. 2019). The region was reportedly seriously impacted by human interference from selective logging for charcoal production and clearing for agriculture (Mittermeier et al. 2019, BirdLife International 2024). A logging company was also observed actively building roads and extracting timber (Mittermeier et al. 2019). Widespread chick and egg collection, and killing of adult birds was also reported, but I. humilis was not specifically mentioned as being impacted by this threat (Mittermeier et al. 2019). Further impacts to the species in Cambodia likely include unsustainable fishing practices, such as poisoning which can lead to direct mortality, as well as explosives which can contribute to declining food sources (BirdLife International 2024).
The Lao PDR population is also seemingly declining from habitat loss (Thewlis et al. 1998). The species was reportedly common in Lao PDR across most forested rivers throughout the 1940s and 1950s, but with rivers and wetlands preferentially settled, suitable habitat has been continually under threat from habitat clearing and degradation from logging (Thewlis et al. 1998). Similar to Cambodia, the species is now restricted to isolated populations in the least disturbed areas across the major catchments, between which dispersal is likely minimal (Thewlis et al. 1998, Duckworth et al. 1999, Fuchs et al. 2007). The isolation of the populations, and the nature of their habitat, puts the species at high risk of local extinction from persecution, incidental disturbance, stochastic events, and habitat degradation (Duckworth et al. 1999, Fuchs et al. 2007). Likewise, although the species is reportedly much more common in northern Myanmar, there have been declines in the historical abundance caused by deforestation, silting of streams, and overfishing (Ferguson-Lees and Christie 2001).
The species is considered to be declining in India and the Himalayan foothills (Ferguson-Lees and Christie 2001, Naoroji 2007, Karuthedathu 2023), to the point it occurs in small and disjunct populations (Lethaby 2005, Praveen 2011), with declines attributed to habitat loss as well as the use of pesticides, particularly in Uttar Pradesh (Ferguson-Lees and Christie 2001, Bezuijen et al. 2008, Karuthedathu 2023). Indeed, the use of pesticides are implicated in the failure of four nesting attempts in northern India (Karuthedathu 2023). Poisoning from DDT is suggested as the cause of fledging failure in Corbett National Park, and eggshells were found with high levels of chemical pollutants (Poole 1995, Naoroji 2007). The most critical declines in the Himalayas appear to have occurred in Nepal, where the species is now considered very rare and is nationally assessed as Critically Endangered (BCN and DNPWC 2011). Along with pesticide use and habitat loss, declines in Nepal are also attributed to the loss of food sources from overfishing (Thiollay 1978 in BCN and DNPWC 2011).
Little is known about the population trends through South-East Asia, but the species is thought to be declining in Peninsula Malaysia (Karuthedathu 2023) and is considered regionally and globally scarce due to the loss of suitable forested river habitat (Bezuijen et al. 2008). The isolated, small, and disjunct distribution of the population also increases the risk of local extinctions, particularly in Cambodia and Laos.
Loss of habitat has been extensive across the species’ range, with c. 24-27% of forest cover lost across the past three-generations (Global Forest Watch 2024, based on data from Hansen et al. [2013] and methods disclosed therein). Most of these losses are attributable to the Sundaic region, where the species is estimated to have lost c. 55% of suitable habitat within the region (Symes et al. 2018), adjusted to c. 40% over the 20.28 years three-generation time (Global Forest Watch 2024). However, rates of forest loss may not accurately depict declines in the population. The species’ breeding habitat is forest-fringed waterbodies (Ferguson-Lees and Christie 2001, Karuthedathu 2023), and the range used to determine rates of forest loss included additional forested regions in which the species may not be resident. Therefore, loss of this additional habitat does not necessarily result in an equivalent population reduction. Furthermore, in some regions the species shows habitat plasticity. The population in southern India is considered stable (Praveen 2011, SoIB 2023), attributable perhaps in part to its adaptation to high food sources occurring in dammed areas (Praveen 2011). The species will also stray onto lakes and dams in the Indian plains (Naoroji 2007), and is recorded in varied habitats in Sabah, including swamps, mangroves, logged forests, and oil palm plantations (Sheldon et al. 2001). Overall, further research is required on the breeding population regionally and globally to fully understand population trends, particularly as protected areas may have the capacity to support large numbers (Bezuijen et al. 2008).
I. humilis is clearly declining across much of its range, and appears to occur in small and isolated populations, particularly in Cambodia and Lao PDR. Though there is still much uncertainty over regional and global trends in its population, especially given it shows some plasticity in its habitat use and tolerance for degradation. Overall, continuing declines of 20-29% are suspected.
I. humilis occurs in the Himalayan foothills, and the western and south-eastern Ghats, India (Lethaby 2005, Ferguson-Lees and Christie 2001, Karuthedathu 2023), Nepal, Bhutan (Rasmussen and Anderton 2012, Karuthedathu 2023), Thailand, Myanmar, Lao PDR, Viet Nam, Cambodia (Fuchs et al. 2007, Goes 2013, Treesucon and Limparungpatthanakij 2018, CBGA 2019, Karuthedathu 2023), Sumatra, Kalimantan, Sulawesi including Peleng, Taliabu, Buru (Eaton et al. 2021), and Manui Islands (Monkhouse et al. 2018), Indonesia, and Sabah, Sarawak, and Peninsula Malaysia (Puan et al. 2020, Karuthedathu 2023), as well as a winter visitor to Hainan, China (MacKinnon and Phillipps 2000, Shing et al. 2007).
I. humilis is dependent on forest-fringed waterbodies with good supplies of fish, typically clear forested hill streams and fast-flowing rivers in lowlands and foothills from sea-level to 1,000 m (Ferguson-Lees and Christie 2001, Karuthedathu 2023). More occasionally, the species occurs around forested lakes and swamps, and will rarely frequent estuaries (Ferguson-Lees and Christie 2001, Karuthedathu 2023). The species does show geographical variation in its habitat, regularly recorded to 1,500m, more locally to 2,500 and as high as 4,250m in Nepal (Ferguson-Lees and Christie 2001). In Sulawesi however, the species will occur near sea-level, and is found in swamps, mangroves, logged forests and oil palm plantations (Sheldon et al. 2001). The species has also adapted to dammed rivers in southern India (Praveen 2011). During the non-breeding season, the species appears to wander more widely, travelling to well-watered areas such as lakes and dams in the Indian plains (Naoroji 2007), and Hanoi (MacKinnon and Phillipps 2000, Shing et al. 2007).
I. humilis is primarily threatened from habitat loss and degradation, and other human induced pressures. The loss and degradation of habitat from selective logging, agriculture, roads and development has led to the decline of the species across most of its range (Thewlis et al. 1998, Ferguson-Lees and Christie 2001, Mittermeier et al. 2019). With the historical preferential settlement of rivers and wetlands resulting in the widespread loss of suitable forested river habitats (Thewlis et al. 1998), the species is considered globally and regionally scarce, and at increased risk from local extinctions due to the isolated and disjunct nature of the population (Duckworth et al. 1999, Fuchs et al. 2007, Bezuijen et al. 2008). The majority of forest loss for this species has occurred in the Sundaic region (Symes et al. 2018, Global Forest Watch 2024), where habitat loss is primarily driven by the conversion of lowland forests into oil-palm and rubber plantations (Descals et al. 2021, Wang et al. 2023). In Lao PDR, habitat loss is exacerbated by habitat clearing for hydroelectric power and particularly gold mining. Even within Dong Ampham, a protected area in eastern Laos where the species has previously been recorded (Davidson et al. 1997), these activities have led to the continual deterioration and loss of habitat (Berryman 2023).
Cumulative impacts to the population come in the form pollution, particularly the use of the pesticides which are implicated in nesting failures in northern India (Poole 1995, Naoroji 2007, Bezuijen et al. 2008), and overfishing which can reduce food availability (Ferguson-Lees and Christie 2001, BCN and DNPWC 2011, BirdLife International 2024).
The species is also targeted to some extent for hunting and/or trade in Indonesia, with two reported incidents in Sulawesi and Borneo, respectively (TRAFFIC 2024), and hunting/trapping may represent a local threat in Cambodia and Lao PDR (Goes 2013 Fuchs et al. 2007, Mittermeier et al. 2019).
Conservation Actions Underway
CITES Appendix II.
This species is a small and small-headed, greyish-brown fishing eagle, similar in size to many members of the genus Buteo. The head and neck are greyer with fine dark streaking, and the belly and thighs are white. The breast is variable in colour, ranging from maroon brown to grey, but the contrast between the breast and belly is not usually very strong. When perched, the wing tips reach the tail tip or fall slightly short. The bill is strong, short, and hooked. The tarsi are mostly unfeathered and pale in colour. As in most other raptors, females are larger than males in size, but they look similar in plumage. In overhead flight, the white in the lower belly and under-tail coverts contrast with rest of the darker body and wings. The trailing wing edges also bulge out at the centre, creating a pinched effect at the base and wrists. The leading edge is sometimes curved forward when soaring, resembling a vulture. Juveniles resemble adults, but are browner and paler, with dark eyes and lightly streaked to unmarked paler underparts. In overhead flight, they show marbled, un-banded, or lightly-banded dark brown remiges, especially the secondaries and inner primaries. Similar species: In adult (definitive basic) plumage, Lesser Fish-Eagle looks superficially similar to Icthyophaga ichthyaetus, but the latter is larger (though size overlap exists). Both species have a white lower belly and undertail-coverts, while the rest of the body is darker (grey/brownish). Though their plumage is similar, the typical calls of both these species are markedly different. Unlike adults, the juveniles differ markedly from each other. Lesser Fish-Eagle juveniles appear like a slightly browner/paler version of the adult, with minimal or indistinguishable streaking on the body, while Gray-headed Fish-Eagle juveniles are much paler and browner, and have a heavily streaked body and pale spotted upper-parts. Sounds: Overall, calls can be described as a querulous cackling, which sound distinctly plaintive and child-like at distance. Calls are loud, nasal, resonant, and varied, including sounds described as hak-hak, or a deep yelping series of ow notes, recalling a large gull. A typical series of calls consists of about 7–10 notes, beginning with a few short-to-medium clucks or wails, followed by longer nyarrrrh/neowoww notes raising in pitch and towards the end, falling off quickly into shorter wails or clucks.
Text account compilers
Richardson, L.
Contributors
Davidson, P., Naoroji, R., Benstead, P., Taylor, J., Elliott, N. & Mahood, S.
Recommended citation
BirdLife International (2024) Species factsheet: Lesser Fish-eagle Icthyophaga humilis. Downloaded from
https://datazone.birdlife.org/species/factsheet/lesser-fish-eagle-icthyophaga-humilis 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.