Justification of Red List category
The population of this impressive raptor is very small. Moreover, given the destruction, disturbance and degradation that is currently being inflicted on its preferred habitat, it is likely to be declining and increasingly fragmented, a circumstance that qualifies it as Endangered.
The population is estimated to number 600-900 individuals, roughly equating to 300-500 mature individuals, based on a 1:1 ratio of adults to juvenile and immature birds, as recorded in past studies (B. van Balen in litt. 2012).
This species is suspected to be in decline at a moderate rate, owing to on-going habitat loss and degradation in the face of human population growth, combined with capture for trade. Recent nest protection may have improved reproductive success, but the benefits accrued may have been countered by an apparent increase in trade of this species following its elevation to national bird.
Nisaetus bartelsi is found on the island of Java, Indonesia, where it is restricted to remaining patches of forest and is consequently scarce (BirdLife International 2001). There have also been some recent records from neighbouring Bali (B. van Balen in litt. 2016). An increase in survey effort and knowledge of the species's home-range size has led to consecutive upward revisions of the global population, now estimated at over 600 individuals (Prawiradilaga 2004), with one estimate of 270-600 pairs (Gjershaug et al. 2004). It is distributed widely throughout much of the island with a recent increase in the number of known localities, although it remains unrecorded from large areas of the north. Although there is no direct indication of a decline, with the species always considered rare, the on-going diminution of forest-cover on Java and increasing trade in the species are certain to have been detrimental (Nijman et al. 2009).
It frequents primary humid forest, although individuals and even nests have been recorded in secondary forest, production forest and tropical semi-deciduous forest, preferring rugged slopes with high vegetation cover (Syartinilia and Tsuyuki 2008). While it occurs from sea-level to high mountains, it is most frequent at 500-1,000 m. Recent extensive research has estimated the average home range size of one pair to be c.400 ha (Gjershaug et al. 2004). The species's dispersal capabilities (and therefore its susceptibility to habitat fragmentation) remain poorly known, but adults appear to be highly sedentary while young birds are the main dispersers (Nijman and van Balen 2003). Juveniles and immatures are recorded in woodland and some cultivated habitats before moving to secondary and primary evergreen forest as adults (Nijman and van Balen 2003); this behaviour suggests that unsuitable habitats may not represent barriers to dispersal. It breeds every two years, principally between January and July, but can breed at any time of year (Prawiradilaga 2006); its reproductive output is generally considered to be low (Syartinilia and Tsuyuki 2008). The preferred diet consists of small mammals but it will take birds, snakes and lizards (Prawiradilaga 2006).
The key threats are habitat loss and trade. The burgeoning human population on Java brings with it intense pressure on natural resources, one aspect of which has been a massive reduction in forest cover, particularly in the lowlands. This threat continues in the form of conversion to agriculture, development and uncontrolled fire, even within protected areas. The species is also sold openly in Javan bird markets, with 30-40 reported in trade each year, and presumably many more undetected. This threat appears to be intensifying, following the elevation of the species to national bird. Individuals are taken from the wild for zoos and wildlife collections, where they tend to fare poorly (Nijman et al. 2009).
Conservation Actions Underway
CITES Appendix II. Several surveys have targeted the species, exploring its distribution and ecology (Prawiradilaga 2006). Strict legislation protects it from hunting or trading, although this is often ineffective. It occurs in several protected areas, including Gunung Halimun, Gunung Gede-Pangrango and Meru Betiri National Parks, although these still face serious problems. An action plan has been compiled and conservation awareness programmes including several training and awareness raising workshops have been initiated (Prawiradilaga 2006, Nurwatha et al. 2004). Project Garuda, which ran in 2002-2003 in Mount Burangrang and Tangkuban Perahu (BuTahu) Nature Reserve forest area, West Java, combined research with conservation activities implementing an extensive awareness raising programme including radio broadcasts, school visits and an exhibition (Nurwatha et al. 2004). A nest protection programme involving local communities has been run successfully (Prawiradilaga 2006). Regular monitoring occurs in Telaga Warna Nature Reserve, Gede-Pangrango National Park and parts of G. Halimum-Salak National Park (Prawiradilaga 2006) and surveys took place around BuTahu in 2002-2003 (Nurwatha et al. 2004). A captive breeding programme has been underway since 1996, although as of 2006 it had failed to produce any offspring (Nijman et al. 2009).
60 cm. Medium-sized, forest-dwelling eagle. Crown and moustachial of adult are black, long crest (often held almost vertically) is black, tipped white. Chestnut sides of head and nape, dark brown back and wings, brown long tail, barred black. Creamy-white throat with dark mesial stripe. Rest of underparts whitish, barred rufous. Immature is similar, but with plainer underparts and duller head. Similar spp. Changeable Hawk-eagle Spizaetus cirrhatus lacks rufous cheeks and long crest. Crested Honey-buzzard Pernis ptilorhynchus is smaller with a shorter crest, uneven tail-barring and less rufous in plumage. Rufous-bellied Eagle Hieraaetus kienerii has shorter crest and extensive white upper breast streaked black.
Text account compilers
Bird, J., Westrip, J., Benstead, P., Khwaja, N., Taylor, J., Tobias, J.
van Balen, B.
BirdLife International (2023) Species factsheet: Nisaetus bartelsi. Downloaded from http://datazone.birdlife.org/species/factsheet/javan-hawk-eagle-nisaetus-bartelsi on 26/09/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 26/09/2023.