Mountain hawk-eagle

The Japanese race averages about 9% larger than mainland race, and also has a proportionately longer tail and longer wings.[19] The populations from Taiwan and the possible ones in Hainan are also probably part of this race.^[12] N. n. orientalis is generally paler than the nominate race with less heavy markings below. The underside in this race has a paler ground colour against much browner and darker barring, often showing less of the warmer or rufous tones typical of mainland mountain hawk-eagles. The throat often has reduced blackish streaking compared to mainland birds and the upper chest can be whitish and nearly unmarked. N. n. orientalis has black mottled or light streaked wing-linings and a small, often vestigial crest compared to the rather ample one of the mainland birds. Sometimes, N. n. orientalis is hypothesized to be a separate species.^[6][20][21] Among standard measurements wing chord of males ranges from 470 to 518 mm (18.5 to 20.4 in) while the female's ranges from 500 to 540 mm (20 to 21 in). In both sexes, the tail ranges from 325 to 395 mm (12.8 to 15.6 in) and the tarsus from 104 to 128.9 mm (4.09 to 5.07 in).^[6][22][23] From a sample of unknown size from the Suzuka Mountains, males of N. n. orientalis were found to average 71.4 cm (28.1 in) and females 76.3 cm (30.0 in) in total length. From the same sample, males had a mean wing chord length of 488 mm (19.2 in), tail length of 342 mm (13.5 in), culmen length of 34 mm (1.3 in) and tarsus length of 113 mm (4.4 in). Meanwhile, females had a mean wing chord length of 516 mm (20.3 in), tail length of 356 mm (14.0 in), culmen length of 37 mm (1.5 in) and tarsus length of 118.2 mm (4.65 in).^[23] Perhaps most surprisingly, the Suzuka mountain birds were not noticeably discrepant in body mass from known weights of mainland mountain hawk-eagles, especially similar to that of the apparently larger hawk-eagles from east-central China. The Suzuka sample as above found males to weigh from 2.2 to 2.7 kg (4.9 to 6.0 lb), with an average of 2.3 kg (5.1 lb), while females were found to weigh from 2.5 to 3.9 kg (5.5 to 8.6 lb), with an average of 3.1 kg (6.8 lb).^[17][23] Another Japanese survey found the smallest male to weigh 1.68 kg (3.7 lb), the lightest known weight known anywhere for the species.^[24]

At one time largish hawk-eagles found in Sri Lanka and southwestern India was deemed to be part of the mountain hawk-eagle species under the subspecies N. n. kelaarti. A 2008 study based on the geographic isolation and differences in call suggest that this be treated as a full species, Nisaetus kelaarti, Legge's hawk-eagle. The full species status of Legge's hawk-eagle appears to be further supported by DNA studies, with an average difference in mitochondrial DNA of 4.3% (usually the minimum difference to differentiate species is considered to be 1.5%).^[15][25][26] Although extremely isolated in distribution from true mountain hawk-eagles, Legge's hawk-eagle is physically distinct as well, often being much paler and less marked below with the throat stripes characteristics of the mountain species often absent (occasionally faint stripes may manifest) being instead largely plain buff about the throat. Like mainland mountain hawk-eagles, Legge's hawk-eagles have a strong crest. The hand in flight on a Legge's is often plain buff in colour (or with some very faint streaking) and the banded wing feathers are rather faded. Legge's hawk-eagle appears to be about 10% smaller than mountain hawk-eagles and was found to differ in almost all bodily proportions from mountain hawk-eagle, with relatively smaller wings but the smaller species also has a larger bill and larger talons than the mountain hawk-eagle.^[6][12][15]

Colouring and confusion species

Adult mountain hawk-eagles are dark brown above with slightly paler edges, which tend to be clearest on median and greater coverts. On adults, the head is fairly rusty above with strong black streaks, though the volume of streaks tends to decrease on the neck, which in turn may suggest a rufous collar. The crest is largely black with a small buffy tip. Their tail is grey-brown, with a whitish tip and rather obscure blackish banding above. The malar area and throat are marked with blackish, ragged and sparse but rather bold stripes which contrast with the rest of their underside which is predominantly barred with rufous over a whitish ground colour. The barring continues, though the white base colour narrows and the rufous becomes a somewhat browner hue, down to the crissum and the legs. In some cases, the colour about the legs has appeared variously chestnut or even blackish.^[6] The underside of the tail is boldly banded with blackish and grey. The juvenile mountain hawk-eagle is also dark brown above but usually has clear cream to whitish feather edges causing the wing coverts to have a scaled effect; meanwhile, the feather bases of median and greater coverts form tawnier mid-wing patches. The juvenile's tail is thinly banded alternately with lighter and darker brown but usually have a whitish tip like the tail of the adult. The juvenile mountain hawk-eagle's underside is all plain buffy to tawny. The underside colour also extends to the head and part of the neck flanks while the crown, cheek, nape and hind-neck all streaked with dark brown. The crest is black with a small white tip. The juvenile leg feathers are whitish. The markings on the underside begin to develop by the 2nd year, starting from the flanks and gradually increasing inward to the breast, but the young hawk-eagles are still quite paler below until their 3rd year, which is also when the tail starts to resemble the adults. Full adult plumage is attained at no later than the 4th year.^[6][16][27] Adults have golden or even yellowish-orange eyes, with juveniles having pale bluish-grey to pale yellow eyes. In the adult the cere is blackish-grey, while in juveniles it is dull-grey. In all ages, the feet range from dull yellow to yellowish white.^[6] In flight, it is notable for its rather prominent head and relatively short rounded wings, an effect emphasized by their broad hands and bulging secondaries, which tend to pinch in at the rear bases. The mountain hawk-eagle is capable of fast, agile flight "with astonishing maneuverability". They usually glide with powerful, shallow beats interspersed with glides on level wings, but soaring birds hold their wings in a shallow V, pressed slightly forward. The wing linings of adults are a rusty similar to flank coloring, becoming paler on forepart and marked with dusky mottling which becomes darker mid-wing. Blackish-brown bars are apparent over greyish ground colour on the secondaries, the feathers here relatively broadly barred with blackish while the primaries are whiter based and darker tipped. Flying juveniles are fairly heavily mottled with white above. Juveniles show more buff to tawny colour below extending to their wing linings while the wing-tips are black, in some cases extending to primary coverts form a vague carpal arc. Juvenile flight feathers are whitish grey with thin and rather faded looking dusky barring, with less white showing at the base of the primaries. Juveniles in flight usually evidence a less distinct subterminal band than do adults.^[6][28]

Confusion of mountain hawk-eagle in all plumages is possible with pale morph changeable hawk-eagles (Nisaetus cirrhatus). However, the latter species only has a vestigal crest in most areas of overlap from northern India to southeast Asia. Furthermore, the changeable is a slighter, more slender bird with a relatively longer tail. The latter species also has narrower wings with more even trailing edges. While soaring, changeable hawk-eagles tend to have flatter wing shape than mountain hawk-eagles. Changeable adults also have streaking rather than heavy rusty barring on their underside, apart from subtle parts of wing linings and flanks, and also have narrower tail bars. In flight, the changeable also has clear white base to their primaries and less whitish on the rump when seen from above. Juveniles of the two species are more easily mistaken but wing proportions always differ, the mountain juveniles usually appear perceptibly bulkier and changeable juveniles (of relevant races) are generally much paler, rather than warm buffy to tawny, on the head and underparts.^[6][12][29] The mountain hawk-eagle also overlaps somewhat in range, in southeast Asia, with Blyth's hawk-eagle (Nisaetus alboniger) and Wallace's hawk-eagles (Nisaetus nanus) but both are much smaller and different in multiple ways (especially the bold black-and-white of adult Blyth's). Another, albeit unlikely, potential source of confusion for the mountain hawk-eagle is with Jerdon's baza (Aviceda jerdoni), which is far smaller, and of a far more compact and chunky build. The baza is somewhat similar in marking to adult mountain hawk-eagles, but the baza lacks feathered legs and has relatively much longer and differently shaped wings. Mountain hawk-eagles can usually be told from the slighter, smaller crested honey buzzard (Pernis ptilorhynchus), beyond the latter being polymorphic, as even most similarly plumaged individual honey buzzards have bare legs, much smaller and slimmer head and bill with a longer neck and deeper wing beats on relatively longer, more slender wings.^[6][30][31]

Vocalisation

Mountain hawk-eagles are silent apart from their breeding season. Their call is a shrill treble note, with a quality often compared to a penny whistle.^[32] Their typical call is often likened to the klu-weet-weet of a green sandpiper (Tringa ochropus) or the kee-kikik of the common green magpie (Cissa chinensis).^[6][15] Sometimes the call is written in Japan as pie-pie-pie or pipipi.^[6][31] The hawk-eagles, including both members of a breeding pair, may call both in flight and while perched. Another call of a rapid bubbling quality, which is considered comparable to that of the little grebe (Tachybaptus ruficollis), is probably produced only during sky-dances.^[6][32] A study in Taiwan diagnosed seven call types consisting of different quality trills in Taiwan during the breeding cycle, including different calls emitted during flight or while perched and food-begging or alarm calls by nestlings.^[33] The calls of mountain hawk-eagles are said to be expertly mimicked by drongos in some parts of the range.^[34][35]

Distribution and habitat

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.

Mountain hawk-eagles are well adapted to living in forests. As is the case for all

One study that reviewed 118 prey items in several nests from southern

pheasants and owls).^[64] Quantitatively rare prey items that have been recorded have including amphibians and, recorded only once, fish.^[58][65]

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.

Formosan serow (Capricornis swinhoei) that were estimated to weigh on average under 2 kg (4.4 lb).^[59][63] Of similar size, in Japan, they took young piglets of the wild boar (Sus scrofa), averaging about 1.75 kg (3.9 lb).^[58] Reportedly, newborn sika deer (Cervus nippon), weighing at least 4.5 kg (9.9 lb), have been preyed upon in Japan as well.^[66] Scavenging of sika deer killed by human hunters has also been reported.^[67] 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).^[12][63] 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).^[17][68]

black snub-nosed monkey (Rhinopithecus bieti), the lar gibbon (Hylobates lar) and the eastern hoolock gibbon (Hoolock leuconedys).^{[74][75][76][77]} 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.^[63][78]

Interspecies predatory relationships

The mountain hawk-eagle overlaps in distribution with several other eagles, including about three species of

spot-bellied eagle owl (Bubo nipalensis) has a very similar central distribution and habitat preferences as the mountain hawk-eagle, and despite being slightly smaller, it goes after exceptionally large prey with perhaps even more aplomb.^[82][83]

In Japan, mountain hawk-eagles are regarded as the fourth largest eagle after the Steller's sea eagle (Haliaeetus pelagicus), the white-tailed eagle (Haliaeetus albicilla) and the golden eagle. Despite the golden eagle race in Japan (A. c. japonica) being much smaller than other races and the larger size of Japanese mountain hawk-eagles, the golden eagle here still has a slight size advantage (about 7% larger) and much larger wings which gives them an advantage at fighting and hunting in open air but less maneuverability.^[31][84][85] While the golden is more a bird of open and rocky environments, the two species prey selection overlaps here (probably more so than mainland populations of the two species), with both taking Japanese hares supplemented by pheasants whenever possible, and this can cause a level of direct competition despite their different preferred habitats.^[23][58][85] In at least one case, a golden eagle attacked and may have preyed upon a mountain hawk-eagle.^[86] On the other hand, a mountain hawk-eagle may have preyed on the young of the black eagle (Ictinaetus malaiensis) in Taiwan.^[87] The mountain hawk-eagle is an occasional predator of a wide diversity of owls. Owl prey known to have been taken has included Asian barred owlet (Glaucidium cuculoides), jungle owlet (Glaucidium radiatum), brown boobook (Ninox scutulata), barn owl (Tyto alba), Ural owl (Strix uralensis) and, once reportedly, even a Eurasian eagle-owl, a species of similar size and power to the hawk-eagle itself.^{[12][59][63][64][88]}

Breeding

The mountain hawk-eagle maintain their home range with a rather spectacular aerial display. Display activities tend to peak within the time period prior to breeding. Their aerial display includes conspicuous and often noisy high circling, both single and mutual, and undulating sky dance of steep dives and climbs with bubbling call uttered at each peak. Like many raptors, the display is likely largely to proclaim ownership to conspecifics but also probably has some function in reinforcing existing pair bonds.

pines, holly, saj (Terminalia elliptica) and moru oak (Quercus floribunda) are often favored at higher elevations. Many nests are often near a steep-edged ravine, or alternately near a natural tree line, freshwater wetland or other environment that provides ample view of the surrounding area.^[6][12][89] Clutch size is usually 1 or 2 but up to 3 eggs in a clutch have been reported in Japan.^[6] It is claimed that one egg is considered the norm in most of the range, as is invariably the case in the related changeable hawk-eagle.^[12][22] The egg is pale clay-colored or reddish in colour with varied freckling of darker red or pure white, and often with blotches and spots of red at the large end.^[22] A sample of egg sizes in the nominate subspecies showed a range of 65 to 72.7 mm (2.56 to 2.86 in) in height, with an average of 69.9 mm (2.75 in) while the range in diameter was 51.2 to 57.4 mm (2.02 to 2.26 in), with an average of 53.8 mm (2.12 in). One egg from N. n. orientalis measured 69 mm × 56 mm (2.7 in × 2.2 in).^[22] It has been claimed that only the female will incubate and will be fed by the male.^[12][22] Hatching dates seem to peak around mid-March in the Indian subcontinent.^[12] At one nest, an immature male was recorded as the mate of an adult female.^[88] In another case, when the female in a pair died during nesting, the following year the male paired with another female and used a nest 200 m (660 ft) from the original nest.^[12]

As is typical of accipitrids, the female takes by far the primary role in brooding and protecting the young, while the male makes prey deliveries into the nest or the nearby nest vicinity. Reportedly, the female is very aggressive if nest is disturbed but male is less so or not at all. The aggressiveness of the female may rival that of the often co-occurring spot-bellied eagle-owl and even outrival the defensive attacks on human by the more powerful African crowned eagle.^[22][90] Cousins such as the Legge's and changeable hawk-eagle do not typically display any aggression or, if so, are very mild in protective behaviour towards humans while nesting.^[12] Apparently, wood-cutters in particular often attract the ire of the female mountain hawk-eagle.^[12] Unlike attacks on humans by crowned eagles and northern goshawks, the attack of mountain hawk-eagle is unlikely to be deterred either by traveling in parties or counterattack. Even when struck with branches, machetes or fist and hit with buckshot by humans, apparently the female will still not cease her attack unless killed or grievously injured.^{[12][91][92][93]} In one case, a local woman in the Kumaon division of northern India fell victim to a "particularly savage" attack by a female mountain hawk-eagle and subsequently died from the injuries sustained.^[12] Cases have been observed in north India where rhesus macaques, northern plains gray langurs (Semnopithecus entellus) and yellow-throated martens, all known nest predators, have been driven off by the female hawk-eagle, in the case of the marten while repeatedly raking the back as it ran off.^[12] The males may make up to two prey deliveries each day but in the area of nests around disturbed village-side forest in India seemed to have problems procuring a sufficient amount of prey. Caches of food may be kept during incubation and the early nestling stage but generally cease thereafter.^[12] After about three weeks, the young are more active and may engage in wing stretching and flapping. At this point, the female takes to a perch about 50 to 100 m (160 to 330 ft) away but continues to watchfully protect the young. The young may soon also be able to feed themselves but are often apparently fed by the mother well after this.^[12] Reportedly family remains together for some time after young fly and the young eagle is fed until they can fly more strongly.^[6] In Japan, an eaglet that hatched in April flew by the end of June.^[94] In India, the minimum amount of time from hatching to leaving the nest was claimed as 53 days.^[12] The breeding cycle lasts for at least 80 days.^[6]

Status

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.^[6] 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.^{[6][12][95][96][97]} 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.^[12][98] 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.^[67] Mountain hawk-eagles may be vulnerable to viruses and helminths as well.^{[99][100][101]} 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.^[1][25] 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.^{[1][6][13][102][103]} 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.^[13]

Notes

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References

Wikimedia Commons has media related to Nisaetus nipalensis.

Wikispecies has information related to Nisaetus nipalensis.

• Ferguson-Lees, James; David A. Christie (2001). Raptors of the World. Illustrated by Kim Franklin, David Mead, and Philip Burton. Boston: Houghton Mifflin.
  OCLC 46660604
  . Retrieved 9 May 2013.