in
Bandipur National Park Changeable hawk-eagles are at home in a variety of wooded and semi-open habitats. Their physical form and flight style is typical of forest-dwelling raptors in general and is often compared to the features of
true hawks or Accipiters in particular larger species such as
goshawks. Like most other forest raptors, changeable hawk-eagles (and
Nisaetus species in general) have a long tail, short broad wings and relatively long but powerful legs, all of which impart greater maneuverability and quicker strike times in denser wooded hunting grounds than other raptorial body plans. The common name hawk-eagle is apparently in reference to their similar adaptations to true hawks. Even compared to the variable prey of large goshawks, the prey selection of changeable hawk-eagles appears to be somewhat indiscriminate and opportunistic. Unfortunately, compared to tropical raptors from the
neotropics and especially
Africa, the life histories of raptors from tropical Asia are generally quite poorly-known, even in the case of easily observed raptors such as changeable hawk-eagles. Therefore, what is known of changeable hawk-eagles dietary biology is largely drawn together based on reliable eye-witness and anecdotal accounts, photographic evidence and wide-ranging bird census surveys, rather than direct, extensive study. Like many tropical forest raptors, they are primarily ambush predators who use concealing foliage to still-hunt from hidden branch or open branch with a leafy background, pouncing fast to take most of their prey on the ground. Like goshawks, changeable hawk-eagles often perch-hunts which are short, low-level flights from perch to perch interspersed with brief pauses, during which they scan for potential prey. Perch-hunting lends them the greatest success when hunting birds that they will capture in the trees. Primary prey by class differed in
West Java, where 62% of prey selected was reptiles, 24% birds and 12% mammals. Elsewhere in India, prey selection at the nest showed what prey species were selected by changeable hawk-eagles but lacked any quantitative data or studies on prey biomass. One study in
Gujarat showed several rather small prey species largely being taken such as the
Indian chameleon (
Chamaeleo zeylanicus),
Oriental garden lizard (
Calotes versicolor), other lizards,
common myna (
Acridotheres tristis),
red-vented bulbul (
Pycnonotus cafer), other birds (including unidentified
parakeets and
gamebirds),
Indian bush rat (
Golunda ellioti) and a
palm squirrel. The identified prey would vary in size only from for a garden lizard to for a myna with the small lizards and chameleons reportedly the most often delivered prey. In
Mudumalai National Park, only three prey types were specified to genera which consisted of
black-hooded oriole (
Orolus xanthornus),
common bronzeback snake (
Dendrelaphis tristis) and an unidentified
giant squirrel. The upper size limit for changeable hawk-eagle prey seems to be fairly liquid and the species is quite the equal of various other
booted eagles in making bold attacks on prey of their own size or larger. Even more impressive accounts and photos show that changeable hawk-eagle can hunt and kill adult mammals with formidable defenses such as
felids and
primates, although it cannot be ruled out that they will usually attack infirm or injured specimens rather than healthy ones. Furthermore, most accounts of attacks on
Old World monkeys show juveniles are by far the most vulnerable members of their troops to hawk-eagle attacks. Cases of either verified, likely or potential predation have been reported on
northern pig-tailed macaque (
Macaca leonina),
crab-eating macaque (
Macaca fascicularis),
toque macaque (
Macaca sinica) and
lion-tailed macaque (
Macaca silenus), including specimens potentially to weigh up to an estimated . A case of predation was photographed by a changeable hawk-eagle on an estimated juvenile
banded langur (
Presbytis femoralis) while possible cases have been reported of predation on juveniles of other
langurs as well as additional larger primates such as
gibbons and
proboscis monkeys (
Nasalis larvatus). While their predator-prey relationship is even more nebulous, the peculiar, smaller but toxic nocturnal primates known as
slow lorises are known to fall prey as well to changeable hawk-eagles. There are several accounts of predation by changeable hawk-eagles on domestic
cats (
Felis catus), though largely kittens, in addition to a case of a large adult
jungle cat (
Felis chaus), with an estimated median weight of , being attacked and killed by one of these hawk-eagles. Apparently, the changeable hawk-eagle is also counted among the predators of calves of
Indian gazelles (
Gazella bennetti). Adults of large
monitor lizards of a few species may be also included in their prey spectrum. Avian kills include adult
Indian peafowl (
Pavo cristatus), of an estimated weight of up to , and the species is considered a threat as well to the similar
green peafowl (
Pavo muticus). Attempted predation on both adult and young
giant ibis (
Thaumatibis gigantea) have been recorded but all known attacks were unsuccessful. Cases of scavenging on carcasses of various
deer and
monkey have been reported as well, in one case a hawk-eagle was filmed chasing an adult
yellow-throated marten (
Martes flavigula) from a carcass. Changeable hawk-eagles were also observing preying on predating on Oriental pied hornbills (
Anthracoceros albirostris).
Food and feeding The habitat selection and overall distribution of the changeable hawk-eagle is largely concurrent with other largish raptors such as the
crested serpent eagle and the
crested honey buzzard, apparently the three species are largely tolerant and non-aggressive towards each other, perhaps surprisingly given the otherwise aggressive habits of hawk-eagles. Unsurprisingly, these species have quite discrepant
ecological niches, especially in terms of their dietary habits. They are also found living alongside the much larger
Philippine eagle (
Pithecophaga jefferyi) and are likely to similarly take smaller prey and avoid direct encounters with the much less numerous giant eagle. Apparently, changeable hawk-eagle are considered likely predators of the slightly smaller
Indian spotted eagles (
Clanga hastata). However, on the contrary, one case of predation was reported in captivity when a
barred eagle-owl (
Bubo sumatranus), which is found in the wild with changeable hawk-eagles in
southeast Asia, killed a changeable hawk-eagle in an aviary.
Breeding The changeable hawk-eagle is, like many raptorial birds, a largely solitary bird otherwise but during breeding, stays in a dedicated pairs that often mate for life. Each pair engages in a territorial display over the fringes of their
home range. This aerial display is usually engaged in by a male but sometimes the female or both members of the pair will engage in displays, often starting with their wings and tail arched upwards in exaggerated poises. During the display, the shoot up vertically and nose-diving or stooping, if the rival hawk-eagle continues to engage the defending individual, they will fly at each other at "lightening speed" doing a complete loop-the-loop turn in air. They often call loudly throughout the display. The parents tend to allow closer approach by humans when living in vicinity of villages. Only one egg is known to be laid by changeable hawk-eagles. The egg tends to be coarse and glossless, largely white but sparely and faintly speckled or blotched with light reddish. Egg sizes were reportedly measured in the nominate subspecies (sample of 40) as ranging from in height with an average of by a diameter of with an average of . In the race
N. c. ceylanensis, a sample of 24 eggs averaged . In
N. c. limnaeetus from northern India, 18 eggs averaged . In the same subspecies, eggs from
Java and
Borneo ranged from in height and from in diameter. In the race
N. c. andamanensis, the average was reportedly but the sample size is unknown. Apparently, the female alone incubates, for a period estimated at 40 days. After the nestling hatches, the female will brood intensively for about 25 days. An Indian nestling was found to weigh at 14 days and grew to by 20 days, having developed a vocabulary of
cheep notes to express hunger and alarm. The eaglet may be preening, standing more and wing flapping by 4 to 5 weeks old, and may also be encouraged to eat at by its mother, however consuming a single food item may take up to 6 hours at this point. At 35 days, the nestling may be brooded progressively less and feather and body size growth accelerates. Within a couple of weeks, prey is delivered (often by both parents at this stage) to nearby branches rather than directly to the nest with the parents calling as they approach, apparently encouraging the young eaglet to venture out of the nest. By 52 days of age, the eaglet is fully-grown but does not fledge until about 60–68 days. The total nest dependency was recorded as 81 days in India. However, the total breeding cycle was recorded as lasting about 112 days in
West Java. ==Status==