Martial eagle
Martial eagle | |
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An adult in the Matetsi Safari Area of western Zimbabwe | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Accipitriformes |
Family: | Accipitridae |
Genus: | Polemaetus Heine, 1890 |
Species: | P. bellicosus
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Binomial name | |
Polemaetus bellicosus (Daudin, 1800)
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Approximate range in green |
The martial eagle (Polemaetus bellicosus) is a large
Range
The martial eagle can be found in most of sub-Saharan Africa, wherever food is abundant and the environment favourable. With a total estimated distribution of about 26,000 km2 (10,000 sq mi), it has a substantial distribution across Africa, giving it a somewhat broader range than other species there like the crowned eagle (Stephanoaetus coronatus) and the Verreaux's eagle (Aquila verreauxii).[6] Although never common, greater population densities do exist in southern Africa and in some parts of east Africa. Martial eagles tend to be rare and irregular in west Africa but are known to reside in Senegal, The Gambia and northern Guinea-Bissau, southern Mali and the northern portions of Ivory Coast and Ghana. From southern Niger and eastern Nigeria the species is distributed spottily through Chad, Sudan and the Central African Republic as well as the northern, eastern, and southern portions of the Democratic Republic of the Congo. In east Africa, they range from Somaliland and Ethiopia more or less continuously south through Kenya, Uganda, Tanzania and in southern Africa from Angola, Zambia, Malawi and southern Mozambique to South Africa.[2] Some of the larger remaining populations are known to persist in Zimbabwe and South Africa. Generally, these birds are more abundant in protected areas such as Kruger National Park and Kgalagadi Transfrontier Park in South Africa, or Etosha National Park in Namibia.[7]
Taxonomy
The
There are no subspecies of martial eagle, and the species varies little in appearance and genetic diversity across its distribution.[2][5]
Description
The martial eagle is a very large eagle. In total length, it can range from 78 to 96 cm (31 to 38 in), with an average of approximately 85.5 cm (33.7 in).
Sexual dimorphism
Martial eagles are highly sexually dimorphic. While females average about 10% larger in linear dimension, in body mass, the sexual dimorphism of martial eagles is more pronounced. Males reportedly can weigh from 2.2 to 3.8 kg (4.9 to 8.4 lb). Seven males in southern Africa averaged 3.17 kg (7.0 lb) and five in another dataset averaged 3.3 kg (7.3 lb).[25][27][28] Twelve adult males in Maasai Mara, Kenya averaged 3.45 kg (7.6 lb).[29] Meanwhile, females can weigh from 4.45 to 6.5 kg (9.8 to 14.3 lb). In southern Africa, seven females averaging 4.95 kg (10.9 lb).[25] Elsewhere, a claim was made of an average of 5.2 kg (11 lb) almost certainly describes a sample entirely of female specimens.[30] In the Maasai Mara, 7 females averaged 4.67 kg (10.3 lb).[29] Reports of males weighing as much as 5.1 kg (11 lb) and females weighing as little as 3.9 kg (8.6 lb) are known but may possibly represent individual eagles misidentified by sex, which is reportedly not infrequent due to mistakes in the field.[28][31][32] Thus the dimorphism by weight is roughly 36% in favor of the female, which is unusually out-of-sync with the linear differences between the sexes. For example, the greater spotted eagle (Clanga clanga), the most sexually dimorphic booted eagle overall with a linear difference between the sexes of 20%, has around the same level of sexual dimorphism by body mass as the martial eagle which show about half as much linear dimorphism.[2][27] In standard measurements, male martial eagles measure 560 to 610 mm (22 to 24 in) in wing chord size, 273 to 280 mm (10.7 to 11.0 in) in tail length and 97 to 118 mm (3.8 to 4.6 in) in tarsus length. Meanwhile, females measure 605 to 675 mm (23.8 to 26.6 in) in wing chord, 280 to 320 mm (11 to 13 in) in tail length and 114 to 130 mm (4.5 to 5.1 in) tarsal length.[2] Overall, the bulk and much more massive proportions of females, which include more robust feet and longer tarsi, may at times allow experienced observers to sex lone birds in the wild.[3][28]
Colouring and field identification
The adult's
There are a few serious identification challenges for the species. The black-chested snake eagle (Circaetus pectoralis) is similar in overall colouring (despite its name it is brown on the chest and the back, being no darker than the adult martial eagle) to martial eagles but is markedly smaller, with a more prominent, rounded head with large eyes, plain, spotless abdomen, bare and whitish legs. In flight, the profile of the snake eagle is quite different, with nearly white (rather than dark brown) flight feathers and much smaller, narrower wings and a relatively larger tail. For juveniles, the main source for potential confusion is the juvenile crowned eagle, which also regularly perches in an erect position. The proportions of crowned eagles are quite distinct from martial eagles as they have much shorter wings and a distinctly longer tail. The juvenile crowned eagle has a whiter head, more scaled back, and spotted thighs and legs lacking in the martial eagle. Beyond their distinct flight profile by wing and tail proportions, crowned eagles have whiter and more obviously banded flight-feathers and tail. Other large immature eagles in Africa tend to be much darker and more heavily marked both above and below than martial eagles.[2][3]
Predatory physiology
Martial eagles have been noted as remarkable for their extremely keen eyesight (3.0–3.6 times human acuity), partly due to their eye being nearly as large as a human's eye. Due to this power, they can spot potential prey from a great distance, having been known to be able to spot prey from as far as 5 to 6 km (3.1 to 3.7 mi) away.
Voice
The martial eagle is a weak and infrequent vocaliser. Little vocal activity has been reported even during the breeding season. The recorded contact call between pair-members consists of the birds, usually when perched, letting out a low mellow whistle, ko-wee-oh. More or less the same vocalisation is known to have been uttered by females when male brings food and repeated mildly by large begging young. During territorial aerial display and sometimes when perched, adults may utter a loud, trilling klee-klee-klooeee-klooeee-kulee. The territorial call may be heard from some distance. Recent fledglings also at times make this call. A soft quolp may be heard, made by pairs around their nest, perhaps being a mutual contact call.[2][3][9] In comparison, the crowned eagle is highly vocal especially in the context of breeding.[9]
Habitat
The martial eagle is to some degree adaptable to varied
Behaviour
The martial eagle spends an exceptional amount of the time in the air, often soaring about hill slopes high enough that binoculars are often needed to perceive them. When not breeding, both mature eagles from a breeding pair may be found roosting on their own in some prominent tree up to several miles from their nesting haunt, probably hunting for several days in one area, until viable prey resources are exhausted, and then moving on to another area.[9][51] However, martial eagles, especially adult birds, are typically devoted to less disturbed areas, both due to these typically offering more extensive prey selection and their apparent dislike for a considerable human presence.[49] Martial eagles tend to be very solitary and are not known to tolerate others of the own species in the area outside of the pair during the breeding season.[52] In general this species is more shy towards humans than other big eagles of Africa, but may be seen passing over populated country at times.[9] The most frequently seen type of martial eagle away from traditional habitats are presumed nomadic subadults. One individual that was ringed as subadult was recovered 5.5 years later 130 km (81 mi) away from the initial banding site. Another martial eagle ringed as a nestling was found to have moved 180 km (110 mi) in 11 months.[2]
Dietary biology
The martial eagle is one of the world's most powerful avian predators. Due to both its underside spotting and ferocious efficiency as a predator it is sometimes nicknamed “the leopard of the air”.
The diet of the martial eagle varies greatly with prey availability and can be dictated largely by opportunity. Remarkably, mammals, birds and reptiles can in turn dominate the prey selection of martial eagles in a given area, with no one prey type globally dominating their prey spectrum.[3][9] In some areas, both mammals and birds can each comprise more than 80% of the prey selection.[9][59] Over 170 prey species have been reported for the martial eagle which is a much higher number than the full prey spectrum of other larger African booted eagles, and even this may neglect some of the prey they take in the little studied populations from west and central Africa and the northern part of east Africa.[3][60] Prey may vary considerably in size but for the most part, prey weighing less than 0.5 kg (1.1 lb) are ignored by hunting martial eagles, with only about 15% of the known prey species averaging less than this. A majority of studies report the average size of prey for martial eagles being between 1 and 5 kg (2.2 and 11.0 lb).[3][61] Average weight of prey taken has been reported at as low as 1.2 kg (2.6 lb).[62] A food study largely based in data from the Great Rift Valley, Kenya, as well as from Maasai Mara, did reinforce a mean prey mass of just over 1.2 kg (2.6 lb) for the species.[63] However, the mean prey body mass is considerably higher in other known dietary studies. In by far the largest dietary study thus far conducted for the martial eagle species (in the Cape Province, South Africa) the estimated mean prey body mass was approximately 2.26 kg (5.0 lb).[61] In Tsavo East National Park of Kenya, the mean estimated body mass of prey was quite similar at approximately 2.31 kg (5.1 lb).[32] Average prey weights in a study of the Maasai Mara was seemingly even higher, at a median between the average prey sizes for each sex of martial eagle at approximately 2.9 kg (6.4 lb).[29] Despite perhaps a majority of prey for this species weighing less than 5 kg (11 lb), martial eagles regular prey size range is claimed at up to 12 to 15 kg (26 to 33 lb).[5][64][65] There is some evidence of prey partitioning (which can be potentially delineated both by prey species and body size of prey items taken) between the sexes. This is typical of raptors with pronounced size sexual dimorphism, as is the case in martial eagles. For instance, in populations where large adult monitor lizards are significant as prey, they only start to appear in prey remains at nests only after the female resumes hunting in the latter part of the breeding season.[3] The species was the focus for a study using web sourced photography to explore the species' diet across its African range, this study revealed new insight into difference in prey composition between regions, and also revealed differences in prey composition between adult and sub-adult birds, with adults found to prey more frequently on bird prey than sub-adults.[66] The sexual dimorphism of kills was verified in studies from the Great Rift Valley and Maasai Mara. One study stated that the mean weight of male kills was 744 g (1.640 lb) and that of females was 1.375 kg (3.03 lb).[63] In Maasai Mara, the mean prey was significantly higher for both males, at about 1.98 kg (4.4 lb), and for females, at about 3.74 kg (8.2 lb).[29]
Mammals
The most diverse class of prey in the diet as known are mammals, with over 90 mammalian prey species reported.
Locally, large numbers are taken of any species of hyrax. The attractiveness of hyraxes as a prey resource may encourage martial eagles to vary their hunting techniques to potentially more time-consuming perch hunting so that they may capture rock hyraxes from rock formations and tree hyraxes from trees, contrary to their usual preference for capturing prey on the ground in the open after soaring high. Ranging in average mass from 2.2 to 3.14 kg (4.9 to 6.9 lb), hyraxes can comprise a healthy meal for a family of martial eagle and are probably among the larger items that male eagles will regularly deliver to nests.[61][75][76][77] Another miscellaneous mammal known to fall prey to martial eagles is the ground pangolin (Smutsia temminckii), although it is not clear the age pangolins that are preyed on and how they are dispatched, considering that adults weigh some 11.6 kg (26 lb) and have a hard keratin shell that is capable of withstanding lion (Panthera leo) jaws when in its rolled-up defensive posture.[3][4][78]
Although far less accomplished and prolific as a predator of
A wide range of
While large accipitrids from around the world are credited with attacks on young or small
While martial eagles usually tend to focus on young fawns, adults of small antelopes are also attacked and taken as prey. Locally favored prey are the dik-diks, one of the smallest kinds of antelope, and every known species may be vulnerable to this eagle.[112] In Tsavo East National Park, Kirk's dik-dik (Madoqua kirkii) were the second most numerous prey species and it was estimated that at least 86 dik-diks are taken in the park over the course of the year by two pairs of martial eagles. At an average of 5 kg (11 lb), these can provide a very fulfilling meal for an eagle family.[32] Adults of other small antelope such as 4.95 kg (10.9 lb) suni (Neotragus moschatus) and 4.93 kg (10.9 lb) blue duikers (Philantomba monticola) are probably also taken with relative ease.[3][61][76] Larger species weighing between 7 and 15 kg (15 and 33 lb) in adults, are known to be preyed upon, including both species of grysbok, steenboks (Raphicerus campestris), klipspringers (Oreotragus oreotragus) red forest duikers (Cephalophus natalensis), and oribis (Ourebia ourebi).[3][104][112][89][113][114] The largest prey taken by martial eagles are common duiker (Sylvicapra grimmia), potentially weighing from 15 to 25 kg (33 to 55 lb) in weight.[4][115] However, one adult female duiker dispatched via strangulation weighed an estimated 37 kg (82 lb), one of the largest known raptorial kill for any species on the African continent.[3]
Among extant birds of prey, only
Birds
Compared to the range and sizes of mammals included in their prey spectrum, birds taken by martial eagles may seem less impressive as a whole, but the morphology of the martial eagle, including large wing surface areas, pronounced sexual dimorphism and relatively long toes, shows that the species is at least partially specialized to hunt avian prey. Birds are universally considered by biologists more difficult to capture than mammals of the same size. In all, more than 50 bird species have been identified as the prey of martial eagles.[2][3][121] The most significant portion of the avian diet is comprised by medium-sized terrestrial upland birds such as guineafowl, spurfowl, francolins[122] and bustards. In total more than a dozen species of the galliform order and the bustard family each have been identified as their prey.[3][4][61] When attacking these ground-loving birds, which are understandably quite easily spooked and usually react to potential danger by flying off, martial eagles almost always try to take them on the ground much like they do mammalian prey. If the birds take flight, the hunting attempt will fail, although a hunting eagle may try to surprise the same birds again.[3] In Niger, the most numerous prey species is apparently the 1.29 kg (2.8 lb) helmeted guineafowl (Numida meleagris).[123] Other guineafowl such as the vulturine (Acryllium vulturinum) and crested guineafowl (Guttera edouardi) are also readily taken elsewhere.[124][125] Guineafowl and spurfowl were stated as the most numerous prey for martial eagles in Kruger National Park.[126] In Tsavo East National Park, the 0.67 kg (1.5 lb) red-crested korhaan (Lophotis ruficrista), perhaps the smallest bustard the eagle hunts, is the most numerous prey taken, comprising about 39% of the prey remains.[32] In the Great Rift Valley and Maasai Mara data, the Coqui francolin (Peliperdix coqui) was reportedly the most regularly identified prey and, in separate studies, helmeted guineafowl averaging 1.48 kg (3.3 lb) made up 12% of the foods in Maasai Mara.[29][63] Medium-sized bustards such as the 1.2 kg (2.6 lb) Hartlaub's bustard (Lissotis hartlaubii) and the 1.7 kg (3.7 lb) karoo korhaan (Eupodotis vigorsii) were oft-taken supplemental prey in Tsavo East and the Cape Province, respectively.[32][25][61] Although these are not usually taken in large numbers, martial eagles are one of the main predators of larger bustards. These may include (averaged between the extremely size dimorphic sexes) the 3.44 kg (7.6 lb) Ludwig's bustard (Neotis ludwigii), the 5.07 kg (11.2 lb) Denham's bustard (Neotis denhami) and even the kori bustard (Ardeotis kori), seemingly the heaviest bustard in the world on average at 8.43 kg (18.6 lb).[4][25][61][66] Attacks on adult male kori bustards, which are certain to be the largest avian prey attacked by martial eagles and are twice as heavy as females, averaging some 11.1 kg (24 lb), can be extremely prolonged. One protracted battle resulted in an injured leg for the eagle and massive, fatal blood loss for the male bustard, which was ultimately scavenged by a jackal by the following morning.[25][127]
Despite its preference for ground-dwelling avian prey, a surprisingly considerable number of water birds may also be attacked.
Reptiles
Reptiles can be locally important in the diet, and they are known to take larger numbers of reptiles than other large African booted eagles. Only relatively large reptiles, it seems, are attacked and many of this prey is also potentially dangerous, so martial eagles have unusually long, gracile tarsi, perhaps an adaptation to dangerous large reptilian prey.
Other reptiles are also occasionally taken. In
Interspecies predatory relationships
For terrestrial predators, including birds of prey, sub-Saharan Africa may be the most competitive environment in the modern world. Due to great diversity of raptors present, each species have shown adaptive specializations, which may consist of various morphological differences that allow them to capitalize on distinct prey selection, hunting methods, habitat and/or nesting habits.[2][3][146][147] The larger booted eagles that dominate the avian food chain in Africa consists of martial eagles, 4 kg (8.8 lb) Verreaux's eagles and 3.64 kg (8.0 lb) crowned eagles, which due to their size and conspicuousness may lend themselves to comparisons. While prey species may overlap in these in southern Africa and some parts of east Africa, where the prey size range of all three eagles averages 1 to 5 kg (2.2 to 11.0 lb), these three powerful eagles differ considerably in habitat preferences, nesting habits and hunting methods. The Verreaux's eagle nests in and hunts around rocky, mountainous kopje to be in close proximity to the much favored prey, rock hyraxes, which they mainly use contour-hunting (hugging the uneven ground to surprise the prey) to capture. The crowned eagle dwells mainly in mature forests, building nests in large interior trees, and is primarily a perch-hunter, watching and listening for monkeys and other prey over a long period. While all three are known to locally favor rock hyraxes, the nesting habitat differences where they overlap are sufficient to allow these birds not to effect one another.[2][3][18][23][25][148] The average prey mass of Verreaux's eagle was similar to that martial eagles, with a pair of studies showing it ranges from 1.82 to 2.6 kg (4.0 to 5.7 lb).[26][149] The mean prey mass of crowned eagles in southern Africa also appears to be similar to that of martial eagles but in west Africa (i.e. Ivory Coast) it was considerably heavier at 5.67 kg (12.5 lb) (which may well be the highest mean prey mass for any of the world's raptors).[136][150] Elsewhere, mean prey masses for the larger booted eagles appears to be considerably smaller than in the larger African species, i.e. single studies for the Spanish imperial eagle (Aquila adalberti) and wedge-tailed eagles showed means of 0.45 kg (0.99 lb) and 1.3 kg (2.9 lb), respectively, while a large number of extensive dietary studies for the golden eagle show its global mean prey mass is around 1.61 kg (3.5 lb).[26][151][152]
More similar in habitat and, locally, prey selection to martial eagles are three medium-sized eagles, the 1.47 kg (3.2 lb)
The martial eagle infrequently hunts other birds of prey, perhaps doing so only slightly more often than do
Territoriality
Despite their rather aerial existence, the territorial display of adult martial eagles is considered relatively unspectacular. Their display often consists of nothing more than the adult male or both members of a pair circling and calling over their home range area or perching and calling near nestlings. Compared to other large African booted eagles, this species infrequently “sky-dances” (i.e. undulation and dramatic movements high in the sky), but some are known with presumably the male martial eagle only engaging in shallow undulations.
Breeding
Martial eagles may breed in various months in the different parts of their range. They are considered a fairly early breeder compared to the average for sub-Saharan Africa birds of prey but breed much less early than
Martial eagles have a slow breeding rate, laying usually one
The newly hatched chick tends to have a two-tone down pattern which is dark grey above and white below, which lightens at about four weeks of age, with the down becoming pale-grey. At 7 weeks, the feathers mostly cover the down and do so completely by 10 weeks except that at that stage the flight feathers are underdeveloped.[3] The new chick is usually quite weak and feeble, becoming more active only after they are 20 days old.[9] The nestlings usually first feeds itself at 9 to 11 weeks old, while it tends to engage in vigorous wing exercises performed from 10 weeks on. Like crowned eagles, males seem to be more active than female youngsters and probably fly sooner too. In one case, a male fledged prematurely at 75 days, however it is possible that male fledging can occur at less than 90 days.[3] Most estimations place fledging as occurring at 96 to 109 days, on average at about 99 days of age. However, after making their first flight, the fledgling usually return to roost in the nest for several days, before gradually moving away from it.[2][3][9] Despite increasing signs of independence (such as flight and beginning to practice hunting), in extreme cases, juvenile birds may remain in the care of their parents for a further 6 to 12 months. A typical post-fledgling care stage will continue for about 3 months after fledging. Despite its ability to fly, it will continue to beg for food from both parents as they are seen. Sometimes, the young eagle from the prior mating season may still be present at the onset of the next breeding season. Juvenile eagles may return to their nest site at as old as 3 years of age, but are unlikely to be fed.[3][9] On the other hand, juvenile martial eagle soar much more readily than crowned eagles and, unlike that species, have been recorded traveling up to several miles from the nest 3 to 4 months after making their first flight.[9] Due to this long dependence period, these eagles can usually only mate in alternate years.
Breeding success is variable and is probably driven by a combination of factors, including prey supply, rainfall levels and distance from human activity.
Conservation issues
The martial eagle is probably naturally scarce, due to its requirement for large territories and low reproductive rates. Nonetheless, the species has been experiencing a major decline in numbers in recent years, due largely to being directly killed by humans. Its
In southern Africa, many martial eagles have taken to nesting on high-tension pylons in areas that are now often absent of large trees, it is one of the few raptors to actually possibly reap more benefit than harm from the presence of these (death by collision with wires and pylons is now one of the worst killers of birds of prey, especially in Europe and southern Africa). However, collision with power lines can be a serious source of mortality, being a common modern problem for especially immature martial eagles, which are less self-assured fliers.[179][198][199][200] Another hazard is caused by steep sided farm reservoirs in South Africa, in which many birds drown. Of 68 eagle drownings there, 38% were martial eagles, the highest percentage of any raptor recorded to be killed by this (again mostly immatures are claimed by this cause of mortality).[3][201] In South Africa, this eagle may have lost 20% of its population in the last three generations due to such collisions.[202] Further exacerbating the problems faced by the martial eagle, habitat destruction and reduction of prey continues to occur at a high rate outside of protected areas. Due to this large swathes of their former breeding range are now unsuitable.[2][5] The preservation of this species depends on education of farmers and other local people, and the increase of protected areas where the species can nest and hunt without excessive disturbance.[5][193]
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- ISBN 0-620-25499-8
External links
- Martial eagle - Species text in The Atlas of Southern African Birds
- Martial eagle at Raptors Namibia
- Martial eagle videos on the Internet Bird Collection
- Object play of an immature martial eagle