The Javan Hawk Eagle Spizaetus bartelsi is endemic to the island of Java (Indonesia) and is confined to the
lowland and hill rainforests and the montane ever-wet rainforests. It has been recorded up to 3,000 m in the
western part of the island, but can also be found at sea level. Until recently it was thought that the species only
occurred on the westernmost and easternmost parts of the island (e.g. Thiollay and Meyburg 1988), but
research conducted by the authors in the central part of Java documented its presence throughout the island in
the best preserved forest areas (Sözer and Nijman 1995b). The most recent estimates (S. van Balen, V. Nijman, unpubl. data), based on extrapolation using average territory size and total area of suitable habitat,
reveal that c. 142-204 breeding pairs (or c. 600-1000 individual birds, including immatures) remain. This low
number, the continuing habitat destruction, as well as the trade in the species, justify its inclusion as Endangered in Birds to watch 2 (Collar et al. 1994).
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| Javan Hawk Eagle |
The field identification of the Javan Hawk Eagle has always been notoriously difficult due to a lack of
adequate descriptions of its plumages in the different stages of its life before it reaches maturity. Although
Bartels (1924) had already drawn attention to the various immature plumages, his descriptions remain
unpublished. Descriptions of the species in standard works on raptors (e.g. Brown and Amadon 1968, Weick
and Brown 1980, Burton 1989) have been inadequate, as most of the illustrations have shown juveniles or
immatures. More than adults, immatures tend to wander and are occasionally seen outside the tall forests; hence they are more easily observed. Even if an ‘adult’ has been depicted, it has at best been an immature showing some adult features, but still lacking the most important characters for field identification (e.g. Hoogerwerf 1949, MacKinnon 1990).
Javan Hawk Eagles can sometimes be seen perching in a large tree inside, or even at the edge of, the forest. The bird occasionally perches in smaller trees near the ground. When perched it often raises its crest. One of the most characteristic features of the adult is the chestnut-coloured head with a black crown and yellow-brown nape (appearing golden in sunshine), which always contrast with the much darker body and
wings. The crest is seldom seen on a flying bird. Flying immatures appear cinnamon-brown from below with a similar, but less pronounced, wing pattern. The flight pattern of the juvenile as depicted in MacKinnon and Phillips (1993) shows a white plumage, an error that might have originated from Kuroda’s confusion of the white juvenile Rufous-bellied Eagle with Javan Hawk Eagle (cf. van Balen 1993). From above the immatures are paler and more mottled than the adults. The wingspan of juveniles seems slightly smaller, while the tail seems longer than those of adults.
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| Javan Hawk Eagle |
The Black Eagle Ictinaetus malayensis is easily recognised by its larger wingspan (especially compared to its tail) and more obvious fingering; immatures can be quite pale brown and, when seen briefly, may cause confusion, but they remain much darker and lack wing-bars. Compared to the Javan Hawk Eagle its flight is less stable, almost unbalanced, resembling kites; typically when soaring the tips of the wings are held upward. The Crested Serpent Eagle Spilornis cheela is smaller, and while soaring holds its wings forward; the wings are held in a characteristic shallow V-shape in a flat plane with the head; in adults the white band on the underwing is clearly visible. The Rufous-bellied Eagle is smaller than the Javan Hawk Eagle and shows no barring; due to its large crest this eagle can resemble a Javan Hawk Eagle, especially when perched or when seen in silhouet only.
Recently a hitherto undescribed plumage phase of the Oriental Honey-buzzard Per nis ptilorhyncus
ptilorhyncus was found in the southern region of West Java (van Balen et al. in prep.). This form (possibly an
immature) lacks the barring on its underparts and shows similarities with immature Javan Hawk Eagle, similar as described for the Sulawesi Hawk Eagle Spizaetus lanceolatus and the Barred Honey-buzzard Per nis celebensis (e.g. Meyer and Wigglesworth 1898, Watling 1983). Although Oriental Honey-buzzards are much smaller and more slender than Javan Hawk Eagles, and their mode of flight (very deep wing beats) is quite different as well, the possible similarity in their plumage has to be taken into account when identifying these species.
Javan Hawk Eagles a medium to large, slender eagle with a total length of c. 60-70 cm. Sexual dimorphism is reversed and appears moderate (Nijman and Sözer, 1996); despite the female being larger and more robust than the male, the overall appearance remains slender. The head is chestnut-brown and the nape is yellow-brown. The crown has dark brown or even black feathers with thin buff margins and the area round the eye appears very dark with pronounced eyebrows. The iris is bright yellow and the bill is dark grey to black with a grey cere. The crest consists of two to four long (up to 12 cm), black feathers with white tips and it may be fan-shaped or pointed (van Balen et al. 1994). The throat can be almost pure white, bordered by dark brown to black moustachial stripes and with a dark brown mesial stripe.
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| Javan Hawk Eagle |
The back and upperwings are dark brown with buff margins to the feathers; the tips of the primaries are black. The inaccuracies in the literature are based on historical misidentifications (e.g. Kuroda 1936, depicts a Rufous-bellied Eagle Hieraaetus kienerii) and the fact that most of the illustrations are based on older depictions and museum skins. In addition, the few flight images in the literature are rather poor, uncharacteristic and, once again, mainly based on immature birds.
The upperside of the tail is dark brown with four black bands and a thin white terminal band. The underside of the tail is greyish-buff with four brown bands and a white margin. The underparts are whitish-buff to white; the breast is marked with bold, dark brown drop-shaped marks, and the belly is narrowly barred dark brown. The talons are quite long with feathers covering the base of the feet.
