Mountain Hawk-eagle

Mountain hawk-eagles are well adapted to living in forests. As is the case for all Nisaetus species, their physical form and flight style is typical of forest-dwelling raptors in general and is often found to be roughly comparable to the features of true hawks or Accipiters in particular larger species such as the occasionally sympatric Northern goshawk (Accipiter gentilis). Like most other forest raptors, mountain 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. Contrary to the suggestion that, based on their physiology, especially their longer wings and tarsus but shorter talon and bill length, when physically compared to the Legge's hawk-eagle implies that the mountain hawk-eagle is morphologically adapted to hunting birds more so than mammals, dietary studies indicate that the mountain hawk-eagle is not necessarily a specialized bird predator but rather a generalist and opportunist like many predators. In fact the small handful of dietary studies of the species show that the mountain hawk-eagle somewhat prefer small mammals as prey but readily takes both birds and reptiles given the opportunity. Typically, the mountain hawk-eagle tends to still-hunt from a concealed perch in foliage, stooping down to take prey. Most prey is taken on the ground. Mountain hawk-eagles have also been observed catching passerines on the wing by giving chase from an ambush or when the prey is flushed by flying low at the canopy level. They will also readily take arboreal mammals and birds from a perch or roost if they're able to fly upon them in an ambush. While most of their prey are relatively small, well within typical prey size range for most raptorial birds, mountain hawk-eagles can take remarkably large prey. Therefore, Brown & Amadon (1986) consider the species as markedly "rapacious and powerful". One study that reviewed 118 prey items in several nests from southern Taiwan, revealed a surprising preferred prey type for mountain hawk-eagles, giant flying squirrels. The Indian giant flying squirrel (Petaurista philippensis) and the red and white giant flying squirrel (Petaurista alborufus), both weighing about 1.65 kg (3.6 lb) on average, accounted for 47.4% of the food items in Taiwan. How they capture these elusive and nocturnal rodents is not clear, but perhaps the flying squirrels’ relatively huge size makes them more conspicuous from the hawk-eagle's lofty perch. A rather smaller true squirrel, the approximately 277 g (9.8 oz) Pallas's squirrel (Callosciurus erythraeus), made up a further 19.5% of the mean diet here. In total, 78.3% of prey taken in the southern Taiwan study was mammalian. However, the fourth most often taken prey species here was the 1.1 to 1.6 kg (2.4 to 3.5 lb) Swinhoe's pheasant (Lophura swinhoii), constituting on average 6.7% of the prey. A study in the Hyōgo Prefecture of Japan reviewed 142 prey items of a single breeding pair. Quantitatively, most prey deliveries by this pair were rather (almost surprisingly) small in body size, whether this is typical of Japanese hawk-eagles is not clear given the lack of comprehensive study. About 17.5% of the nest prey deliveries were unidentified small birds, of an estimated mass of 17.5 g (0.62 oz) (mostly brought by the male), while 7.7% of prey deliveries were unidentified medium-sized birds, of an estimated mass of 175 g (6.2 oz). These were followed by the merely 20 g (0.71 oz) Japanese shrew mole (Urotrichus talpoides) which constituted 7% of prey deliveries (again largely by male) . The most often delivered prey (18.2% of her 44 deliveries) by the female once she resumed hunting were larger class Elaphe snakes, in excess of 100 cm (39 in) length and 325 g (11.5 oz). Overall, the estimated size of nest prey deliveries here ranged from a 5 g (0.18 oz) Japanese grass lizard (Takydromus tachydromoides) to several Japanese hares (Lepus brachyurus) weighing an estimated mean of 1.9 kg (4.2 lb), the latter presumably constituting a majority of the prey biomass. In another study, the mean size of Japanese hares caught was apparently estimated as somewhat larger at about 2.5 kg (5.5 lb). In Jim Corbett National Park, India, prey reportedly consisted largely of smallish or medium-sized birds (albeit probably larger than those in the above Japanese study) such as mynas, doves, parakeets, nightjars, owls and village poultry. In the Russian Far East, apparently the most important prey types were reported as Manchurian hares (Lepus mandshuricus), a close cousin and of the same size as the Japanese hare, and hazel grouse (Tetrastes bonasia), while most of the remainder of the diet consisted of a mixture of smallish mammals like (moles, hedgehogs and flying squirrels) and largish forest birds (woodpeckers, pheasants and owls). Quantitatively rare prey items that have been recorded have including amphibians and, recorded only once, fish. While most of the prey mentioned above is of relatively modest size, the mountain hawk-eagle is not infrequently reported to attack prey of quite large sizes, including prey equal to their own size or larger. Mountain hawk-eagles have been reported to attack young ungulates but often relatively very young and small ones, probably close to a neonatal state. In Taiwan, they took the young of Formosan serow (Capricornis swinhoei) that were estimated to weigh on average under 2 kg (4.4 lb). Of similar size, in Japan, they took young piglets of the wild boar (Sus scrofa), averaging about 1.75 kg (3.9 lb). Reportedly, newborn sika deer (Cervus nippon), weighing at least 4.5 kg (9.9 lb), have been preyed upon in Japan as well. Scavenging of sika deer killed by human hunters has also been reported. Larger avian prey has been taken by mountain hawk-eagles, including adult Indian peafowl (Pavo cristatus) weighing up to an estimated 4 kg (8.8 lb). In Echizen-Kaga Kaigan Quasi-National Park, Japan, mountain hawk-eagles have been recorded attacking exclusively relatively large water birds on several occasions namely: the 1.12 kg (2.5 lb) mallard (Anas platyrhynchos), the 1.45 kg (3.2 lb) grey heron (Ardea cinerea), the 2.53 kg (5.6 lb) greater white-fronted goose (Anser albifrons) and the 2.77 kg (6.1 lb) bean goose (Anser fabalis). Carnivorans taken by mountain hawk-eagles can also be relatively large as well as potentially dangerous. An estimated 1.8 kg (4.0 lb) kit of a Japanese badger (Meles anakuma) was preyed upon by a female. Meanwhile, four adult Chinese ferret-badgers (Melogale moschata), weighing on average about 1.3 kg (2.9 lb), were taken in Taiwan, while a Japanese marten (Martes melampus) of the same estimated weight was taken there by a female hawk-eagle. Sable (Martes zibellina) are also likely at threat from these birds. More impressive carnivoran prey dispatched by this species included an adult yellow-throated marten (Martes flavigula) weighing an estimated 2.75 kg (6.1 lb), an adult red panda (Ailurus fulgens) weighing an estimated 4.5 kg (9.9 lb) and reportedly adult raccoon dogs (Nyctereutes procyonoides), which weigh an average of 6.5 kg (14 lb), not to mention (in a similar size range) an occasional domestic cat (Felis silvestris catus) taken by this species. Of a similarly impressive nature in size and defensive temperament are primates, of which the mountain hawk-eagle is an occasional predator. However, a rather large portion of primate prey, such as monkeys, are taken as infants or juveniles, and most but not adults killed by them are perhaps are likely to be previously injured or sickly. Taking even infant monkeys can be provide some risk for hunting hawk-eagles due to the protective nature of mothers as well as the overall monkey troops. For example, Formosan rock macaques (Macaca cyclopis) recorded to be taken in Taiwan were infants, weighing only an estimated 500 to 700 g (1.1 to 1.5 lb). An Assam macaque (Macaca assamensis) juvenile taken by a mountain hawk-eagle weighed an estimated 2 kg (4.4 lb). Cases of possible predation have also involved rhesus macaques (Macaca mulatta) in the Indian subcontinent. The mountain hawk-eagle is also considered a potential or confirmed threat to some larger primates (though largely or entirely younger, more vulnerable members of their troops) including: the François' langur (Trachypithecus francoisi), the black snub-nosed monkey (Rhinopithecus bieti), the lar gibbon (Hylobates lar) and the eastern hoolock gibbon (Hoolock leuconedys). However, the most impressive primate kill was an adult Japanese macaque (Macaca fuscata), estimated to weigh somewhere between 8.3 and 10 kg (18 and 22 lb), that was taken alive and subsequently dismantled by a large (presumed female) mountain hawk-eagle.

Both the northern and southern limits of this widely found raptor are surprisingly poorly known to this day, with historic records suggesting that the species may take up residence hundreds of kilometers north of its accepted range and year-around reports of this species from areas formerly considered only to be visited by wintering migrant or vagrant hawk-eagles. The mountain hawk-eagle is distributed through the Himalayas, extending from northeastern Pakistan through north India in at least the states of central Jammu and Kashmir, Himachal Pradesh and Uttarakhand, continuing into Nepal, Bhutan to northern Assam thence southward into the north and east Burmese highlands, west and peninsular Thailand, also the northern parts of Laos and probably Vietnam. Their range continues eastward into southeastern China where they may be found in Yunnan, Guangxi and Guangdong Province northward in the east to the lower reaches of the Yangtze in Anhui and Zhejiang. Their range also extends to Hainan, an offshore island of China. Mountain hawk-eagles are additionally found in the island nations of Taiwan and Japan, with the highest concentration known on northern islands such Hokkaido but they may be found on nearly all the islands of Japan. The mountain hawk-eagle has been recorded under the status of "rare breeder" in areas much farther north than is conventionally accepted as part of their range, such as far eastern Mongolia and the landlocked, extreme southern part of the Russian Far East such as in Primorsky Krai. To this date, the IUCN has not updated the range maps for mountain hawk-eagles to reflect the species’ presence in these areas, although their status as continual breeders here may still need confirmation. Through much of their range, mountain hawk-eagles are typically sedentary but both adults and young hawk-eagles sometimes also disperse in descent from higher grounds in winter and it may be characterized as a partial migrant. There are several recorded cases of the species wandering in north India down into Indo-Gangetic plains. In Bhutan, fragmentary information suggest short-distance altitudinal movements are not infrequent. Relatively low volumes of migrant mountain hawk-eagles were detected in Nepal, however. With a fair amount of consistency, the hawk-eagles found in the northern part of southeast Asia range into more lowland areas of Burma, eastern Thailand and peninsular Malaysia, they are also similar movements to lowlands in Japan with some Japanese ones moving to the Korean peninsula. In some of the areas above such as Thailand and Malaysia (mainly far northern part of country), year-around reports of mountain hawk-eagles may suggest small, isolated pockets of residency and/or breeding occurring. Mountain hawk-eagles have been recorded as a vagrant in Hong Kong and Cambodia. Broader vagrancy has been reported in the case of a mountain hawk-eagle that turned up in the island of Borneo. The mountain hawk-eagle tends to reside in dense hill and montane forests at any point up to the tree line. They are mainly found in various wooded foothills. Typically, primary evergreen or mixed forests are preferred, with the presence of nearby streams a plus. However, in some areas the species can range into second growth. In non-breeding times, mountain hawk-eagles may sometimes wander through wooded plains and briefly near fairly developed villages and even cities. In Japan, they reportedly entirely avoid woods near urban areas. Elevations the species has been known to live at in the Himalayas are mostly 600 to 2,800 m (2,000 to 9,200 ft) above sea-level. However, they've been recorded at elevations of up to 4,000 m (13,000 ft) in northern Yunnan. In Japan, they usually reside somewhat lower than in their mainland haunts, typical at between 250 and 1,500 m (820 and 4,920 ft). Mostly only during winter, the species has been recorded (albeit seldomly) down to 200 m (660 ft) or even lower as vagrant.

Though it is not considered a globally threatened species, the mountain hawk-eagle is never more than uncommon to rare locally. It occurs over a rather large distributional range that apparently extends over 19 million square kilometers. However, in estimations from the late 1990s, it was considered doubtful that the density of mountain hawk-eagle was high enough to reach 10,000 individuals, even with the now-separated Legge's hawk-eagle included at that time and all juveniles. High levels of various habitat degradation and deforestation is probably the primary driver of declines throughout the range. In particular, the increasing density of human populations in northern India, southeastern China and Japan are likely to continue to facilitate declines in forest quantity and quality. Likely more localized and minor threats from humans are persecution as occasional killers of domestic poultry. Despite their popularity in Asian falconry, it is unlikely gathering of hawk-eagles for this is a significant problem. Lead poisoning from consuming carcasses of sika deer, left there by human hunters using lead bullets, have resulted in the death of some mountain hawk-eagles. Mountain hawk-eagles may be vulnerable to viruses and helminths as well. Similar threats are faced by all Nisaetus hawk-eagles, with only the changeable hawk-eagle shown to be resilient to human interferences and not in decline at the species level. The Japanese population of mountain hawk-eagles is particularly showing signs of decline. In the 1990s, the Japanese population was estimated at 900–1,000 total individuals and may have reduced even more so today from that figure. As the species is a K-strategist like all eagles, it was feared that the ongoing population reduction of N. n. orientalis might lead to loss of genetic diversity, and consequently inbreeding depression. However, genetic diversity was shown to be still considerable at present.