Approximate range in green (contrary to this map, the martial eagle is absent from the densely forested regions in Central and West Africa)
The martial eagle (Polemaetus bellicosus) is a large eagle found in open and semi-open habitats of sub-Saharan Africa. It is the only member of the genus Polemaetus.
The martial eagle is a very large eagle, with a length of 78–96 cm (31–38 in), weight of 3–6.2 kg (6.6–13.7 lb) and a wingspan of 188–260 cm (6 ft 2 in–8 ft 6 in). Among standard measurements, the wing chord is 56–67.5 cm (22.0–26.6 in), the tail is 27.2–32 cm (10.7–12.6 in), the tarsus is 9.7–13 cm (3.8–5.1 in). This is the largest eagle in Africa and is the fifth heaviest (on average) eagle in the world.
The adult’s plumage consists of dark grey-brown coloration on the upperparts, head and upper chest, with slightly lighter edging to these feathers. The body underparts are white with blackish-brown spotting. The underwing coverts are brown, with pale flight feathers being streaked with black. The female is usually larger and more spotted than the male. The immature is paler above, often whitish on the head and chest, and has less spotted underparts. It reaches adult plumage in its seventh year. Martial eagles have a short erectile crest, which is often not prominent. It often perches in a quite upright position, with its long wings completely covering the tail. The bill, at 5.5 cm (2.2 in), is strong and the legs are feathered to the heavy, powerful feet. There are few serious identification challenges for the species. The black-chested snake eagle is smaller, with a relatively more prominent head and white lining the flight feathers. The crowned eagle, which also regularly perches in an erect position, has distinctly shorter wings and a distinctly longer tail and, though its plumage is fairly variable, it is more scaled on the back and it has distinctive barring on the underparts and the wings. More so than any other African eagle, the martial eagle is often seen only in flight.
Martial eagles have been noted as remarkable for their extremely keen eyesight (3.0–3.6 times human acuity). Due to this power, they can spot potential prey from a very great distance.
Range and habitat
The martial eagle can be found in most of sub-Saharan Africa, wherever food is abundant and the environment favourable. It is never common, but greater population densities do exist in southern Africa, especially 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.
Its preferred habitat is open woods and woodland edges, wooded savannah and thornbush habitats. It is not found in dense tropical forests such as the Guinean and Congolian forests, but needs trees to nest in and to use for obstruction while hunting. In southern Africa, they have adapted to more open habitats, such as semi-desert and open savanna with scattered trees, wooded hillocks and, as a recent adaptation, around pylons. They usually seem to prefer desolate or protected areas. The territory can vary greatly in size from more than 1,000 km2 (390 sq mi) to areas where nests are less than 10 km (6.2 mi) distant. This disparity is due to differences in food supply.
The martial eagle is one of the world’s most powerful avian predators and, among African raptors, only the crowned eagle is comparable in predatory dominance. The martial eagle is an apex predator, being at the top of the avian food chain in its environment and, if in healthy condition, having no natural predators. Although the ranges of the martial and crowned eagles occasionally abut each other, the species have differing habitat preferences, with the crowned preferring denser forests as opposed to the wooded savanna preferred by the martial eagle, and the two are not known to compete directly. The diet of the martial eagle varies greatly with prey availability and can be dictated largely by opportunity. One study of the eagles in Kruger National Park found that 45% of their diet was made up of birds, particularly game birds and Egyptian geese. Reptiles, especially lizards like monitor lizards and snakes, including Cape cobras, boomslangs, puff adders, both green mambas, and even young black mambas and African Rock Pythons, made up 38%. The remaining 17% of prey in the study were made up of mammalian prey (which is detailed below).
Among bird prey, martial eagles often choose to predate medium-sized ground-dwelling species such as francolins, guineafowl or bustards. Other birds predated have included young ostriches, storks, herons, other waterfowl, hornbills and quelea flocks. At one eyrie, the remains of six spotted eagle-owls were counted. Martial eagle occasionally predate adult Kori bustard, which are possibly the heaviest flying animal alive today. In some areas mammals constitute the greater part of the diet than birds or reptiles. Among regular mammal prey are hares, hyraxes, mongooses, squirrels, springhares, rats, genets, foxes, baboons, other monkeys, young warthogs dikdiks, young impala and various other young or small antelope. Large and formidable prey are not unheard of, with carnivores such as caracal, servals and black-backed jackals having been killed by this eagle. Martial eagles have predated adult duikers weighing up to 37 kg (82 lbs), perhaps the heaviest live prey item recorded for any wild raptor. Oversized prey, being any that are notably heavier than the eagle itself, are returned to repeatedly after the kill for feeding by both members of a breeding pair, since it is too heavy to take flight with or carry in flight. However, most prey items weigh under 5 kg (11 lb). Martial eagles may additionally attack domestic livestock, including poultry, lambs and young goats, but this is never a great part of the diet.
The martial eagle hunts mostly in flight, circling high above its territory, and stooping sharply to catch its prey by surprise. Prey may be spotted from 3 to 5 kilometers away. On occasion, they may still-hunt from a high perch or concealed in vegetation near watering holes. Unusually for a bird of its size, it may hover while hunting. Birds are typically killed on the ground or in trees, but there are records of bird prey being killed in mid-flight.
Young bird in Masai Mara, Kenya
Martial eagles may breed in various months in different parts of their range. The mating season is in November through April in Senegal, January to June in Sudan, August to July in northeast Africa and almost any month in eastern Africa, though mostly in April–November. Martial eagles have been thought to have no distinctive display flight, but they do engage in a subtle one, with the males flying mildly around in circles. Rarely, the female joins him and the pair grasp talons with each other. During the breeding season, these typically silent birds utter a loud cry klee-klee-klee-kloeee-kloeee-kuleee. They build their nests in large trees, often placing them in the main fork of tree at 6–20 m (20–66 ft) off the ground, though nests have been recorded from 5 to 70 m (16 to 230 ft) high, in the highest cases on top of the tree canopy. Often trees used are on the sides of cliffs, ridges, valley or hilltop, with one nest having been found within a cave. In the karoo of South Africa, they have also nested on electric-power pylons. The nest is a huge construction of sticks. In the first year of construction, the nest is 1.2 to 1.5 m (3.9 to 4.9 ft) in diameter and 0.6 m (2.0 ft) deep. After regular use over several years, the nests can regularly measure in excess of 2 m (6.6 ft) in both diameter and depth. Martial eagles have a slow breeding rate, laying usually one egg (rarely two) every two years. The egg is incubated for 45 to 53 days and the chick fledged at 96 to 104 days. Despite increasing signs of independence (such as flight and beginning to practice hunting), juvenile birds will remain in the care of their parents for a further 6 to 12 months. Due to this long dependence period, these eagles can usually only mate in alternate years.
The martial eagle is probably naturally scarce, due to its requirement for large territories and low reproductive rates. However, the species has been experiencing a major decline in numbers in recent years, due largely to being directly killed by humans. Its conservation status was uplisted to Near Threatened in 2009 and to Vulnerable in 2013 and another uplisting is already expected. In many areas where they come into contact with humans, eagle populations have decreased greatly through persecution via shooting and poisoning. The reasoning behind such persecution is that martial eagles are taken as a predatory threat to livestock. Despite this perception, in reality domestic animals constitute only a small proportion of the species’ diet, whereas the presence of eagles is a sure sign of a healthy environment. Indirect threats, such as collision with power-lines, are also a common modern problem for martial eagles. Another hazard is caused by steep sided farm reservoirs, in which many birds drown. In South Africa, this eagle may have lost 20% of its population in the last three generations due to such collisions. Further excerbating the problems faced by the martial eagle, habitat destruction and reduction of prey continues to occur at a high rate outside of protected areas. The preservation of this species depends on education of farmers, and the increase of protected areas where the species can nest and hunt.