Verreaux's eagle

This species was first described by René Primevère Lesson in his 1830 publication, ''Centurie zoologique, ou choix d'animaux rares, nouveaux ou imparfaitement connus, as Aquila Verreauxii''. The species' name commemorates the French naturalist Jules Verreaux, who visited southern Africa in the early 19th century and collected the type specimen for the French Academy of Sciences. Verreaux's eagle is part of a broad group of raptors called "booted eagles" which are defined by the feature that all included species have feathering over their tarsus, whereas most other accipitrids have bare legs. Included in this group are all species described as "hawk eagles" including the genera Spizaetus and Nisaetus, as well as assorted monotypical genera such as Oroaetus, Lophaetus, Stephanoaetus, Polemaetus, Lophotriorchis and Ictinaetus. The genus Aquila is distributed across every continent but for South America and Antarctica. Up to 20 species have been classified in the genus but the taxonomic placement of some of the traditionally included species has recently been questioned. Traditionally, the Aquila eagles have been grouped superficially as largish, mainly brownish or dark-colored booted eagles that vary little in transition from their juvenile to their adult plumages. Genetic research has recently shown the Verreaux's eagle is included in a clade with its nearest relatives, the sister species Bonelli's eagle (A. fasciatus) and African hawk-eagle (A. spilogaster), as well as the golden eagle. More distantly related are the sister species pair, the wedge-tailed eagle (A. audax) and Gurney's eagle (A. gurneyi). Closely related to this clade are the Cassin's hawk-eagle (A. africanus). The identification of the smaller, much paler-bellied A. fasciatus and A. spilogaster as members of the clade was a surprise, given that they were previously included in the genus Hieraaetus. Cassin's hawk-eagle has been assigned to both the Hieraaetus group and the Spizaetus/Nisaetus "hawk-eagle" group but is now known based on this genetic data to also nest within Aquila. and have been transferred to the genus Clanga. The small-bodied Wahlberg's eagle (H. wahlbergi) has been traditionally considered an Aquila species due to its lack of change from juvenile to adult plumage and brownish color but it is actually genetically aligned to the Hieraaetus lineage. == Description ==

. Verreaux's eagle is a very large eagle. It measures long from the bill to the tip of the tail, making it the sixth longest eagle in the world. Males can weigh and the larger females weigh . The average weight is approximately , based on the weights of 21 eagles of both sexes. Other reported mean body mass measurements of Verreaux's eagles were lower however, with seven unsexed birds averaging , while four unsexed eagles in an additional study averaged . In yet another study, seven males were found to average and seven females to average . In another group of weighed eagles, four females were found to average . It is the seventh or eighth heaviest living eagle in the world. In average mass and overall weight range, if not linear measurements, the Verreaux's is very similar in size to its occasional competitor, the martial eagle, which is regularly titled the largest of the African eagles. It also rivals the martial and golden eagles as the largest extant member of the "booted eagle" clan. It has a wingspan of . The wing chord of the male is and that of the female is . Among other standard measurements in the Verreaux's eagles, both sexes measure in tail length and in tarsus length. Immatures have a strongly contrasting golden crown and a rufous or ginger nape and mantle. They have small white streaks on the forehead and black on their cheeks. The throat is dark streaked, the lower throat is pale brown and the upper-chest is brown. Full adult plumage is probably attained in 5 to 6 years. The Verreaux's eagle is essentially unmistakable, especially in adulthood. No other black-colored raptor in its range approaches this species' large size, nor possesses its distinctive patterns of white. The golden eagle is of similar size or marginally larger size and the two species are the heaviest living Aquila species and measure only marginally less than the slightly lighter-weight Australasian wedge-tailed eagle in total wing and bill-to-tail length. While the juvenile Verreaux's eagle is quite different from the adult's, its plumage is no less distinctive. No other accipitrid shares the mottled brownish body, blackish wings with large white patches or contrasting whitish, rufous and golden color around the head and neck. The flight profile of Verreaux's eagle is also distinctive: it is the only Aquila species other than the golden eagle to soar in a pronounced dihedral, with the wings held slightly above the back and primaries upturned at the tip to make a V shape. In the Bale Mountains of Ethiopia and possibly in some parts of the Arabian Peninsula and the southwestern edge of the Middle East, the ranges of the golden and Verreaux's eagles overlap, but the golden is a mostly brown bird and shares none of the Verreaux's black plumage. The immature golden eagle has white patches on its underwing as do Verreaux's, but they are less extensive than those of the latter species. The wing shape also differs from the golden's, as the Verreaux's eagle has very broad outer secondaries and a relatively narrow pinch at the base of the primaries, whereas the tapering of a golden eagle's wing is more gradual. The Verreaux's eagle wings have variously been described as paddle, spoon or leaf shaped. Imperial eagles too have white markings on their wing coverts, but are different in flight profile (flatter winged) and overall coloration (dark brown). Voice . This species is largely silent, though is arguably a stronger vocalist than its close cousin, the golden eagle. Chicking and chirruping sounds like that of a young turkey or francolin, ', have been heard in various contexts, such as pairs being reunited. More striking sounds are loud, ringing ', ' or ' calls used as contact calls or during intruder chases. Various screams, barks, yelps and mews have been heard to be issued at potential mammalian predators. The young emits feeble chirps at first, later more likely to cluck like the adults. ==Habitat and distribution==

Verreaux's eagle has specific habitat requirements and is rare outside of its particular habitat type. It lives in kopjes, which are dry, rocky environments in anything from rocky hills to high mountains amongst cliffs, gorges and inselbergs often surrounded by savanna, thornbush and sub-desert. of Sudan southward through that country to 16°N in Eritrea, along the northern mountains of Somalia, in much of Ethiopia (mostly the central, mountainous spine), possibly some mountains in northeastern Uganda, Kenya, easternmost Democratic Republic of the Congo and possibly Tanzania. in Zambia (especially the escarpments bordering Lake Kariba to the gorges below Victoria Falls), in Zimbabwe (especially east of the central plateau), Mozambique, Eswatini, Lesotho and down into South Africa, where they largely inhabit the Karoo, along the cliffs of the Great Escarpment, the Cape Fold Mountains and Cape Peninsula. A somewhat more sparse distribution is known in Botswana, western Namibia and southwestern Angola (in the Serra da Chela). Elsewhere in Africa, the Verreaux's eagle may be found but tends to be rare and only spottily seen, such as in eastern Mali, northeastern Chad, the Aïr Mountains of Niger and southwestern Cameroon (where known only as a vagrant). In 1968, only a single record of Verreaux's eagle (from Jordan) was known from outside of Africa, but now it is known to be a rare breeder in the Middle East: from a handful of immature records and territorial adult behavior, breeding has been inferred in Lebanon, Israel, Oman, Saudi Arabia and Yemen. File:Balancing Rocks in Matopos National Park.jpg|A kopje in the Matobo Hills, home to the highest density of Verreaux's eagle File:Aquila verreauxii-nes, Roodekrans, Walter Sisulu NBT, a.jpg|A nest at the Walter Sisulu National Botanical Garden in Roodepoort, South Africa File:Waterval in Muldersdrif se Loop, Walter Sisulu NBT, b.jpg|View of two nests used by the same pair at the Roodekrans, beside Witpoortjie Waterfall, Walter Sisulu Botanical Garden == Dietary ecology ==

. Two species comprise considerably more than half of (often more than 90% of) the Verreaux's eagle's diet: the Cape hyrax (Procavia capensis) and the yellow-spotted rock hyrax (Heterohyrax brucei). Few other accipitrids are as singularly specialized to hunt a single prey family as Verreaux's eagles, perhaps excluding the snail kite (Rostrhamus sociabilis) and the slender-billed kite (Helicolestes hamatus) with their specialization on Pomacea snails. Not even accipitrids named after their staple food are known to be as specialized, i.e. the bat hawk (Macheiramphus alcinus), palm-nut vulture (Gypohierax angolensis), lizard buzzard (Kaupifalco monogrammicus) and perhaps the rufous crab hawk (Buteogallus aequinoctialis). Certainly, the Verreaux's eagle has the most conservative diet of Aquila species, though the diet is more diverse in South Africa than in Zimbabwe. In the Matobo Hills of Zimbabwe, the two hyraxes comprised 1,448 out of 1,550 eagle prey items recorded at eyries just after the breeding season from 1995 to 2003. In the same area, from 1957 to 1990, 98.1% of the diet was made up of rock hyrax. Elsewhere in Tanzania, the diet is more mixed, with 53.7% of the remains from 24 nests made up of hyrax. In a nest in South Africa, 89.1% of the remains from a sampling of 55 were of hyrax. No detailed statistics are known but the hyrax are likely to the main prey in every population and have been mentioned to dominate the diet in Mozambique, Malawi Around 400 hyrax may be taken through the year by a pair with young. Hunting hyrax cooperatively has been recorded, with one eagle of a pair flying past and distracting the prey while the other strikes from behind. Verreaux's eagle may knock hyraxes off cliffs and take arboreal prey from treetops, but it usually kills on the ground. However, the Cape hyrax has a wider distribution than the yellow-spotted and the Verreaux's eagle may hunt the Cape hyrax almost exclusively outside of the long band of eastern Africa where the smaller species is distributed. The foot of the Verreaux's eagle is reportedly larger than a human hand. The enlarged rear hallux claw of a Verreaux's at an average of in 4 females and in 5 males is quite similar in size to that of a golden eagle. Other prey Verreaux's eagle are capable of taking diverse prey, but this is infrequent in areas with healthy rock hyrax populations. Cases where more diverse food is brought to the nest are usually either considered to be areas where rock hyrax populations have declined or areas where eagles occupy home ranges which included non-rocky habitat such as savanna, which are described by Valerie Gargett as "poor food areas" due to their lack of hyrax. In such areas, about 80% of prey is mammalian. Other prey types recorded have included small (mainly juvenile) antelopes, hares, rabbits, meerkats (Suricata suricatta), other mongooses, monkeys, squirrels, cane rats, bushbabies and lambs (Ovis aries) and kids (Capra aegagrus hircus). Francolin (Francolinus ssp.) and guineafowl (Numina ssp.) as well as waterfowl, herons, egrets, bustards, pigeons, crows (Corvus ssp.), doves, chickens (Gallus gallus domesticus) and a great sparrowhawk (Accipiter melanoleucus) have been among the recorded avian prey. Avian prey ranging in size from alpine swift (Tachymarptis melba) to adult male Denham's bustards (Neotis denhami). In Tanzania, out of a sample size of 41 from 26 nests, 53.7% of remains were of hyraxes, 29.3% of francolins, guineafowl and chickens, 12.2% of antelopes, 2.4% of hares and rabbits and 2.4% of mongoose. Carrion either fairly frequent or none at all. An impressive range of mammalIan carnivores is known to be taken by Verreaux's eagles. Some of these may consist of genets, mongooses, felids, bat-eared foxes (Otocyon megalotis) and even black-backed jackals (Canis mesomelas), apparently carnivores can become more significant in human developed areas. Although any prey weighing over is rarely taken, some ungulates hunted by Verreaux's eagles can be considerably larger. A Verreaux's eagle was observed to hunt and kill a mountain reedbuck lamb estimated to weigh . The smallest known mammalian prey was a Cape gerbil (Gerbilliscus afra). Interspecies competition when it enters the latter's home range, but the falcon quickly veers off when the eagle presents its talons. Although it is the most specialized predator of rock hyrax in the world, it does not have monopoly on this prey. Many other predators also hunt rock hyraxes, which thus puts them in potential competition with the Verreaux's eagles. Amongst the other very large eagles which are widely found in sub-Saharan Africa, both the crowned eagle and the martial eagle may also locally favor rock hyraxes in their diets. However, these species have highly different habitat preferences and hunting techniques. The crowned eagle, a forest-dwelling species, is primarily a perch-hunter and can spend hours watching for prey activity from a prominent tree perch. The martial eagle is a dweller mainly of lightly wooded savanna and often hunts on the wing, soaring high and watching for prey activity with its superb vision, quite unlike the contour-hunting technique used by Verreaux's eagles. While the habitats of crowned and Verreaux's eagle keep them segregated enough to likely eliminate competition, confrontations between Verreaux's and martial eagles have been recorded. Although somewhat larger and more powerful, the martial eagle is relatively less nimble in the air and there is a case where a martial eagle was robbed of rock hyrax prey by a Verreaux's eagle. An apparent predation attempt on a full grown juvenile Rüppell's griffon (Gyps rueppellii) was abortive. A unique opportunity to study Verreaux's eagle living with its closest extant cousin, the golden eagle, has been afforded in the Bale Mountains of Ethiopia. The two species, with similar habitat preferences, were observed to defend their territories from one another exclusively, with many cases of goldens chasing Verreaux's eagles out of their respective territories in flight and only one of Verreaux's chasing the goldens. However, since the golden eagles prefer hares and Verreaux prefers rock hyraxes, they actually seem to have no deleterious effect on each other's breeding activities. African hawk-eagles (Aquila spilogaster) may also take a few hyraxes, but are likely to avoid direct conflicts with their much larger cousins, so will tawny eagles (Aquila rapax). Due to the formidable range of competitors it pays for Verreaux's eagle to be cautious from the moment it bears down on its prey. Cases where pirating has been attempted has involved diverse carnivores like caracals and jackals. In at least one case, a Verreaux's eagle was observed to be displaced off a rodent-kill (likely a cane-rat) by an Ethiopian wolf (Canis simensis). Unlikely competitors for nest sites are known to have included baboons and even geese. As is often the case with reintroduced eagles (i.e. seen even in the huge harpy eagle (Harpia harpyja)), reintroduced Verreaux's eagle may lose their fear of other predators to their own detriment and one such bird fell victim to a caracal. Cases where Verreaux's eagles have swooped at leopards are not likely competitive but are more likely to try to displace the cat from their territory, and such attacks have occasionally had fatal results for the birds. This species is not normally aggressive to humans but may swoop uncomfortably close when the nest is being investigated. ==Behavior==

Territoriality and movements A rough estimated average of home range size in Verreaux's eagle is . The Matobo Hills reportedly has one of the greatest breeding densities known of any large eagle and territories are extremely stable through seasons and years. Such stable distributions are expected of long-lived raptors living in the tropics with a relatively stable food supply outside the seasonal variation of temperate zones. While Matobo Hill home ranges ranged from , most were observed to include about the same amount of kopje habitat (up to ). At troughs, eagles may temporarily disappear or switch to alternate prey. This is only especially marked in drought periods and on average occurs once every 20 years. Some authors consider the Verreaux's eagle to be a partial migrant, others describe it as sedentary. This is more a matter of terminology than unclear behaviour, since this species is well known to behave like almost all raptors that breed in Sub-Saharan Africa. That is the young wander relatively widely once dispersed from their parent's territory but the adults generally remain sedentary on their home range for the remainder of their lives. Verreaux's is the most cliff dependent of all eagle species, in the late 1970s only 3 known nests were in trees. A new nest takes up to four months to construct, with some repair being typical upon each use. Both sexes participate in the nest construction, though the female usually takes the lead. Egg laying may occur from November to August in Sudan and Arabia, October to May in Ethiopia and Somalia, year around in East Africa (with a peak of June to December) and anywhere from April to November in Africa from Zambia southwards. At one time no cases of two young successfully reaching the fledging stage were known, however a couple of cases of two healthy fledglings from a nest have been recorded. Siblicide is regularly observed in raptorial birds, including unrelated families like owls and skuas and is common, even typical, in Aquila eagles. The behaviour is most commonly explained as a kind of insurance policy, with the second nestling existing both to act as a backup if the first egg or nestling perishes and to mitigate the stressful workload demanded of the parent raptors in feeding, brooding and defending the young. The odds of survival for the second fledging are better in the golden eagle and other temperate-breeding Aquila eagles, possibly due to a shorter nesting stage in these species. In roughly 20% of golden eagle nests and in some cases, such as prey-rich areas of North America, about half of the nests will successfully produce two fledglings. In the Verreaux's eagle, no food is given to the hatchling in the first 36 hours, thereafter they are regularly fed. Early in the fledging stage, the young is brooded up to 90% of the time. After 20 days, parents spend up to 20% of time with their eaglet around the nest, not brooding in daylight after 21 days. Feathers appear through the down at about 34 days, by 60 days feathers cover the down. In Equatorial Africa, the eaglet fledges from the nest at 95–99 days, though sometimes as little as 90 days further south. In the golden eagle, the fledging stage is roughly 35 days shorter. The young Verreaux's eagle takes its first flight and then returns to the nest for the first fortnight. In the early fledging period, the male brings more food, later it is largely the female. At some point during the post-fledging stage, she ceases to roost with the young one and sits with the male at some distance, a behaviour that seems to vary from nest to nest in timing. After 45–50 days, food is caught by the parents but is likely eaten by themselves and not brought to the young. After leaving the nest, family parties may be together for up to 6 months. The eaglet grows stronger after the first month and accompanies the parents on hunting forays away from the nest. It often breeds every year, occasionally only on every other year. ==Population and status==

. Verreaux's eagles' nests are estimated to have a 40–50% success rate per year. The estimated average lifespan is 16 years. However, in South Africa, the overall number of pairs declined from 78 in 1980 (25 in reserves) to 27 in 1988 (with 19 in preserves). In the Sisulu Botanical Garden, artificial feeding has been contemplated to maintain a breeding pair in the face of continuing declines of available wild prey. ==References==