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Орел Верро
Verreaux's Eagle (Black Eagle), Aquila verreauxii, at Walter Sisulu National Botanical Garden, Gauteng, South Africa (28825027073).jpg
В национальном ботаническом саду Уолтера Сисулу в Рудепурте , Южная Африка
Научная классификация edit
Королевство:Animalia
Тип:Хордовые
Класс:Авес
Заказ:Accipitriformes
Семья:Accipitridae
Род:Aquila
Разновидность:
A. verreauxii
Биномиальное имя
Aquila verreauxii
Урок 1830 года
Aquila verreauxii distr.png
Ареал орла Верро в зеленом

Орел Verreaux в ( Aquila verreauxii ) является большой, в основном African , хищных птиц . Его также называют черным орлом , особенно в Южной Африке , что может привести к путанице с индийским черным орлом ( Ictinaetus malayensis ), который обитает далеко на востоке в Азии. [2] Орел Верро обитает в холмистых и горных районах южной и восточной Африки (частично простираясь до Чада ), а также очень локально в Западной Африке , на Аравийском полуострове и на юге Ближнего Востока.. Это один из наиболее специализированных видов ястребов в мире, его распространение и история жизни связаны с его любимым видом добычи - каменными даманами . Когда популяции даманов сокращаются , этот вид с переменным успехом выживает на другой добыче, такой как маленькие антилопы , дикие птицы , зайцы , обезьяны и другие позвоночные животные. Несмотря на высокую степень специализации, орел Верро, с точки зрения сохранения, в исторические времена жил относительно хорошо. Одна популяция этого вида на холмах Матобо в Зимбабве., возможно, является наиболее изученной популяцией орлов в мире, которая постоянно подвергалась подробным исследованиям с конца 1950-х годов. [2] [3] Как и все орлы , этот вид принадлежит к таксономическому отряду Accipitriformes (ранее включенному в Falconiformes ) и семейству Accipitridae , которые в просторечии могут упоминаться как accipitrids или raptors.

Таксономия [ править ]

Иллюстрация из описания вида Уроком, опубликованного в 1830 г. [4]

Этот вид был впервые описан Рене Первером Уроком в его публикации 1830 года Centurie zoologique, ou choix d'animaux rares, nouveaux ou imparfaitement connus как Aquila Verreauxii . [5] Название вида дано в честь французского натуралиста Жюля Верро , который посетил юг Африки в начале 19 века и собрал типовой образец для Французской академии наук . [6] [7]

Орел Верро является частью обширной группы хищников, называемых « орлы-сапоги », для которых характерно то, что у всех включенных видов есть оперение на предплюсне, тогда как у большинства других акципитридов ноги голые. В эту группу включены все виды, описанные как «орлы-ястребы», включая роды Spizaetus и Nisaetus , а также различные монотипные роды, такие как Oroaetus , Lophaetus , Stephanoaetus , Polemaetus , Lophotriorchis и Ictinaetus . Род Aquila распространен на всех континентах, кроме Южной Америки иАнтарктида . До 20 видов были отнесены к роду, но таксономическое положение некоторых из традиционно включенных видов недавно было поставлено под сомнение. Традиционно орлы Aquila на первый взгляд сгруппированы как большие, в основном коричневатые или темные орлы-сапоги, которые мало различаются при переходе от молоди к взрослому оперению.

Генетические исследования недавно показали, что орел Верро включен в кладу со своими ближайшими родственниками, родственными видами орла Бонелли ( A. fasciatus ) и африканского орла-ястреба ( A. spilogaster ), а также с парой более далеких сестринских видов клинохвостый орел ( A. audax ) и орел Герни ( A. gurneyi ). [8] Тесно связаны с этой кладой беркут и орел -ястреб Кассина . [8]Некоторые из родственных связей внутри этой группы долгое время подозревались на основании морфологического сходства между крупными видами. [9] Идентификация меньших по размеру, с гораздо более бледным животом A. fasciatus и A. spilogaster как членов клады была неожиданностью, учитывая, что они ранее были включены в род Hieraaetus . [3] [10] [11] Ястреб-орел Кассина был отнесен как к группе Hieraaetus, так и к группе «орла-ястреба» Спизета / Нисита, но теперь известно, что на основании этих генетических данных он также гнездится в пределах Акилы . [8]

Другие крупные виды Aquila , восточный имперский орел ( A. heliaca ), испанский имперский орел ( A. adaberti ), желто-коричневый орел ( A. rapax ) и степные орлы ( A. nipalensis ), теперь считаются отдельными, сплоченная клада, которая в результате конвергентной эволюции приобрела некоторые характеристики, сходные с характеристиками предыдущей клады. [10] [11] Генетически « подорлы » ( C. pomarina , C. hasata и C. clanga ) были обнаружены как более близкие родственники длиннохохлатого орла.( Lophaetus occipitalis ) и черный орел , [10] [12] и был передан к роду Clanga . [8] Род Hieraaetus , традиционно включающий орла- сапога ( H. pennatus ), маленького орла ( H. morphnoides ) и орла-ястреба ( H. ayresii ), состоит из гораздо более мелких видов, которые на самом деле являются самыми маленькими птицами, которых называют орлы вне неродственного рода змеевиков Spilornis . Этот род был недавно исключен многими авторитетными источниками и теперь иногда также включается вАквила , хотя не все орнитологические союзы последовали этому примеру в этой переклассификации. [3] [11] [13] Орел Уолберга с мелким телом ( H. wahlbergi ) традиционно считался разновидностью Aquila из-за того, что у него не менялось оперение ювенильного на взрослый и коричневатый цвет, но на самом деле он генетически связан с Hieraaetus происхождение. [10] [14]

Описание [ править ]

Портрет Акилы Верроуксии
Взрослый орел Верро в полете в Южной Африке .

Орел Верро - очень большой орел. Его длина от клюва до кончика хвоста составляет от 75 до 96 см (от 30 до 38 дюймов), что делает его шестым по длине орлом в мире. [15]Самцы могут весить от 3 до 4,2 кг (от 6,6 до 9,3 фунтов), а более крупные самки весят от 3,1 до 7 кг (от 6,8 до 15,4 фунтов). Средний вес составляет примерно 4,19 кг (9,2 фунта), исходя из веса 21 орла обоих полов. Другие зарегистрированные средние измерения массы тела орлов Верро были ниже: семь бесполых птиц в среднем весили 3,32 кг (7,3 фунта), в то время как четыре несексуальных орла в дополнительном исследовании имели в среднем 3,72 кг (8,2 фунта). В другой группе взвешенных орлов было обнаружено, что четыре самки в среднем весили 4,6 кг (10 фунтов), что более чем на килограмм больше, чем средний самец. Это седьмой или восьмой самый тяжелый из ныне живущих орлов в мире. По средней массе и общему весу, если не по линейным измерениям, Verreaux очень похож по размеру на своего случайного конкурента, боевого орла., который регулярно называют самым крупным из африканских орлов. Он также соперничает с боевыми и беркутами как самый крупный из ныне живущих членов клана «орлов-сапог». [15] [16] [17] [18] [19] [20] Он имеет размах крыльев от 1,81 до 2,3 м (от 5 футов 11 дюймов до 7 футов 7 дюймов). [15] [21] хорды крыла самца 56,5 до 59,5 см (22,2 до 23,4) и в том , что самки от 59 до 64 см ( от 23 до 25 в). Среди других стандартных размеров орлов Верро, оба пола имеют длину хвоста от 27,2 до 36 см (от 10,7 до 14,2 дюйма) и длину предплюсны от 9,5 до 11 см (от 3,7 до 4,3 дюйма) . [9] [15]За исключением небольшого преимущества в размерах самок, взрослые самцы и самки физически неотличимы друг от друга. [15] Взрослые орлы Верро в основном имеют угольно-черный цвет. [9] Желтый цвет цевы (клюв - серый металлический), кольцо для глаз и «брови» - все это выделяется на контрасте с черным оперением. [15] Еще более заметным у летающих птиц, если смотреть сверху, является белый цвет на спине, крупе и верхней части хвоста, а также на части лопаток, которая образует V-образное пятно, хотя эта особенность частично скрыта у птиц, сидящих на насесте. [9] У взрослых особей также есть заметные белые окошки на перьях крыльев в области запястья (у основания первичных пальцев), когда они летят как сверху, так и снизу. [9][15] Клюв толстый, голова выступает на относительно длинной шее, а ноги полностью оперены. [15]

Ювенильный орел Верро.

Оперение молодых и неполовозрелых особей заметно отличается от оперения взрослых особей. В целом они темно-коричневого цвета. [22] У неполовозрелых особей сильно контрастирует золотая корона, а также рыжий или рыжий затылок и мантия. У них на лбу небольшие белые прожилки, а на щеках - черные. Горло с темными прожилками, нижняя часть горла бледно-коричневая, а верхняя часть груди коричневая. [15]Остальная часть нижней стороны коричневая, за исключением черновато-рыжего или кремового цвета живота и слегка обозначенных кремовых бедер и ног. Перья верхнего и верхнего кроющих крыла у молодых птиц коричневые с белыми прожилками, а остальные перья хвоста и крыльев почти черные. Перья крыльев, если смотреть снизу в полете, демонстрируют значительные беловатые пятна с более обширными белыми пятнами, чем обычно наблюдаются на оперении взрослых. У неполовозрелых особей темно-коричневый радужная оболочка и желтоватые лапы. [9]Черные перья увеличиваются с 2 до 5 лет среди россыпи перьев с коричневыми кончиками, хотя контрастные кремовые брюки сохраняются до 3-го года. К 4-му году жизни они выглядят темно-серо-коричневыми с желтоватым пятном на затылке и пятнами сохраняющихся буроватых перьев. В конце полувзрослой фазы примерно в 5 лет оперение практически неотличимо от взрослого. [23] Полное оперение взрослой особи, вероятно, достигается через 5-6 лет. [24]

Орел Верро практически безошибочен, особенно в зрелом возрасте. Ни один другой хищник черного окраса в этом ареале не приближается к крупному размеру этого вида и не обладает характерными белыми узорами. [15] Беркут имеет одинаковый или немного больший размер, и эти два вида являются самыми тяжелыми из ныне живущих видов Aquila, и их размеры лишь немного меньше, чем у более легкого австралийского орла с клиновидным хвостом, по общему крылу и длине клюва до хвоста. . [3]Хотя молодой орел Верро сильно отличается от взрослого, его оперение не менее характерно. Никакой другой акципитрид не разделяет пестрое коричневатое тело, черноватые крылья с большими белыми пятнами или контрастный беловатый, рыжеватый и золотистый цвет вокруг головы и шеи. Профиль полета орла Верро также отличительный: это единственный вид Aquila, кроме беркутов, который парит в ярко выраженном двугранном состоянии , с крыльями, расположенными немного выше спины, и первичными крыльями, перевернутыми на вершине, чтобы образовать V-образную форму. В горах Бейла в Эфиопии и, возможно, в некоторых частях Аравийского полуострова и на юго-западной окраине Ближнего Востока., ареалы золотых орлов и орлов Верро пересекаются, но золотистый - это в основном коричневая птица, и у него нет черных оперений Верро. Незрелый беркут имеет белые пятна на нижнем крыле, как и у Верро, но они менее обширны, чем у последнего вида. Форма крыла также отличается от золотой, поскольку у орла Верро очень широкие внешние второстепенные элементы и относительно узкая выемка в основании основных элементов, тогда как крыло беркута сужается более плавно. Крылья орла Верро по-разному описывались как лопатки, ложки или листы. [9] [15] У имперских орлов тоже есть белые отметины на кроющих крыльях, но они отличаются по профилю полета (более плоские крылья) и общей окраске (темно-коричневый). [15]

Полет орла Субадульта Верро

Голос [ править ]

Пленный орел Верро в Южной Африке .

Этот вид в основном молчит, хотя, возможно, он более сильный вокалист, чем его близкий родственник, беркут. [15] Пикирование и щебетание, как у молодой индейки или франколина , пюк , можно было услышать в различных контекстах, например, при воссоединении пар. Более поразительные звуки - это громкие, звонкие звонки вау-у-у-у , х-у-у-у или в- у-у-у-у, используемые как контактные звонки или во время преследования злоумышленников. Были слышны различные крики, лай, визг и мяуканье, издаваемые потенциальными хищниками из числа млекопитающих. [9] [15] Молодые поначалу издают слабое чириканье, а позже они с большей вероятностью будут кудахтать, как взрослые. [9]

Среда обитания и распространение [ править ]

Копье на холмах Матобо , где обитает самая большая плотность орла Верро.

У орла Верро есть особые требования к среде обитания, и они редко встречаются за пределами своего конкретного типа среды обитания. Он живет в kopjes , которые сухие, каменистые среды в чем - нибудь от скалистых гор до высоких гор среди скал , ущелий и инзельберг часто окружены саванне , терновый куст и суб-пустыни . [15] Это часто встречается в засушливых районах со среднегодовым количеством осадков менее 60 см (24 дюйма).

Это самая высокая точка над уровнем моря в Эфиопии и Восточной Африке, где она находится на высоте до 4000 м (13000 футов) над уровнем моря. [9] орёл Verreaux является найдено из Марры [25] из Судана на юг через эту страну [26] до 16 ° N в Эритрее , [27] вдоль северной гор Сомали , [28] в большей части Эфиопии ( в основном центральный горный хребет) [29], возможно, некоторые горы на северо-востоке Уганды , [30] Кения , крайняя восточная часть Демократической Республики Конго и, возможно,Танзания . [15]

Юго - восточная Африка является сердце орла диапазона Verreaux в: они встречаются в большинстве горных хребтов в Малави , но и для Ниика плато , в Mafinga Хиллз и Lulwe Хиллз, [31] в Замбии (особенно уступы , граничащих озеро риба в ущельях ниже Водопад Виктория ), в Зимбабве (особенно к востоку от центрального плато), [32] Мозамбик , Свазиленд , [33] Лесото и вниз в Южную Африку , где они в основном населяют Кару , вдоль скалБольшой откос , горы Кейп-Фолд и полуостров Кейп . [34] [35] [36] Несколько более редкое распространение известно в Ботсване , западной Намибии и юго-западной Анголе (в Серра-да-Чела ). [37] [38] В других частях Африки орла Верро можно встретить, но, как правило, он встречается редко и редко встречается, например, в восточной части Мали , северо-востоке Чада , [39] в горах Айр в Нигере [40] и на юго-западе Камеруна.(где известен только как бродяга). [41] В 1968 году только одна запись об орле Верро (из Иордании ) была известна за пределами Африки, но теперь известно, что это редкий заводчик на Ближнем Востоке: по нескольким незрелым записям и территориальному поведению взрослых особей, разведение было выведено в Ливане , [42] [43] Израиль , [44] Оман , [45] Саудовская Аравия [46] и Йемен . [47] [48]

Диетическая экология [ править ]

Немногие акципитриды столь же специализированы, как орел Верро. Один из двух предпочитаемых ими видов добычи: мысский даман .

Два вида составляют значительно больше половины (часто более 90%) диеты орла Верро: мысовый даман ( Procavia capensis ) и каменный даман с желтыми пятнами ( Heterohyrax brucei ). Немногие другие акципитриды так же специализированы для охоты на одну жертву, как орлы Верро, возможно, за исключением змеевика- улитки ( Rostrhamus sociabilis ) и тонкоклювого коршуна ( Helicolestes hamatus ), специализирующегося на улитках Pomacea . Даже аккипитриды, названные в честь их основного продукта питания, не считаются такими специализированными, как ястреб-летучая мышь (Macheiramphus alcinus ), пальмовый гриф ( Gypohierax angolensis ), канюк-ящерица ( Kaupifalco monogrammicus ) и, возможно, рыжий ястреб-краб ( Buteogallus aequinoctialis ). Конечно, у орла Верро самая консервативная диета среди видов Aquila , хотя диета в Южной Африке более разнообразна, чем в Зимбабве . [49]

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.[50] In the same area, from 1957 to 1990, 98.1% of the diet was made up of rock hyrax.[2] In a sample size of 224 from 102 nests in Serengeti National Park in Tanzania, 99.1% of the remains were of hyrax.[51] Elsewhere in Tanzania, the diet is more mixed, with 53.7% of the remains from 24 nests made up of hyrax.[52] In a nest in South Africa, 89.1% of the remains from a sampling of 55 were of hyrax.[53] 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,[54] Malawi[31] and Botswana[55] Around 400 hyrax may be taken through the year by a pair with young.[15] The entire distribution of the species neatly corresponds with that of the two species of rock hyrax.[9] To date, there are no known instances of Verreaux's eagle hunting the two species of tree hyraxes.[49]

In the first 10 years of constant observation of the population from the Matobo Hills, only two kills were witnessed. However, enough hunting behavior has been ultimately observed to give a good idea how a Verreaux's eagle obtains its prey.[23] This species most often forages in low-level quartering flight, with the rock hyraxes chiefly caught after a rapid, somewhat twisting dive in the few seconds after the eagle surprises the hyrax. Like the golden eagle, Verreaux's eagle uses natural contours of the ground in rocky and mountainous habitats to increase the element of surprise, as hyraxes (appropriately considering their diverse range of predators) tend to be highly wary.[15][49] Verreaux's eagle have been known to hunt from a perch, though rarely.[9][56] 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.[15] The daily estimate food requirements of this species are around 350 g (12 oz), nearly a third more than that of a golden eagle despite the latter's marginally heavier body weight.[23] Rock hyraxes are often difficult to observe for humans, other than a glimpse, but a Verreaux's eagle can fly out and then return to the nest with a kill in the matter of a few minutes.[23]

Of the two species regularly taken, the yellow-spotted rock hyrax can weigh from 1 to 3.63 kg (2.2 to 8.0 lb) with an average of 2.4 kg (5.3 lb), although specimens from Zimbabwe are noticeably heavier and larger than specimens from Serengeti National Park. Cape hyrax, weighing from 1.8 to 5.5 kg (4.0 to 12.1 lb) with average of around 3.14 kg (6.9 lb), can be even larger than the Verreaux's eagles themselves, so can be more difficult to kill. Yellow-spotted rock hyraxes are more often taken in the Matobo Hills, perhaps because of their smaller size or its more diurnal habits. Adult rock hyraxes are disproportionately selected, perhaps due to being out in the open more regularly. In Cape hyraxes, 1- to 2-year-old males are particularly vulnerable, since they are forced to disperse at sexual maturity. Juvenile hyraxes constituted from 11–33% of prey remains in the Western Cape while 18% of hyraxes killed were juveniles in Matobo Hills. Because of their greater weight, Cape hyraxes are frequently either consumed at the kill site (putting the eagle at risk of losing prey to competing predators or to attack by large mammalian carnivores) or are decapitated and brought to the nest or perch. Fewer skulls or jaws of Cape hyraxes than of yellow-spotted rock hyraxes have been found at nest sites.[57][58] 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.[49] In comparison to the golden eagle, Verreaux's eagle has a foot pad that about 20% wider, which may be an adaptation to taking the bulky and broad-backed rock hyrax.[59] The foot of the Verreaux's eagle is reportedly larger than a human hand.[60] In South Africa, where the Cape hyrax is the main prey species, the estimated mean size of prey taken to the nest is around 2.6 kg (5.7 lb), perhaps twice as heavy as prey taken by some nesting golden eagles.[59] However, the mean size of prey taken by Verreaux's eagle in the Matobo Hills, with more yellow-spotted rock hyrax, was around 1.82 kg (4.0 lb), around the same estimated weight as prey taken by golden eagles in Europe and smaller than the average estimated mass of prey taken to golden eagle nests in regions like Scotland or Mongolia.[3][61]

Other prey[edit]

An adult Verreaux's eagle carrying avian 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.[2][62] In such areas, about 80% of prey is mammalian.[9] Verreaux's eagles that are less specialized have diets and hunting capacities that are similar to those of the golden eagle, although the latter species often subsists on hares, rabbits, ground squirrels or grouse for about half or two-thirds of its diet, a portion still comprised by rock hyrax in the Verreaux's.[2][3] One study accumulated records of Verreaux's eagle preying on at least 100 prey species.[63] 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.[15][64] Avian prey ranging in size from 102.6 g (3.62 oz) alpine swift (Tachymarptis melba) to 7.26 kg (16.0 lb) adult male Denham's bustards (Neotis denhami).[16][65][66] 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.[52] Tortoises made up 145 of 5748 from 73 sites (2.5%) in South Africa. Rarely, snakes and lizards may also be taken and even termites have been eaten by this species.[15][23]

In South Africa, the commonest foods were (in descending order of preference): Cape hyrax, Smith's red rock hare (Pronolagus rupertris), meerkat, mountain reedbuck (Redunca fulvorufula), goats and sheep, scrub hare (Lepus saxatilis), Cape francolin (Francolinus capensis), helmeted guineafowl (Numida meleagris), yellow mongoose (Cynictis penicillata) and Angulate tortoise (Chersina angulata).[15] In “poor food areas” of the Matobo Hills, three nests included 53.6% hyrax, 10.7% cane-rats, 7.1% monkeys, 7.1% mongoose and 3.6% antelope.[2] From 1997 to 2005 in the same area, non-hyrax prey (each representing less than 10 out of 1550 prey items at nests) included white-tailed mongoose (Ichneumia albicauda), steenbok (Raphicerus campestris), domestic goat, vervet monkey (Chlorocebus pygerythrus), Jameson's red rock hare (Pronolagus randensis), helmeted guineafowl, Swainson's francolin (Pternistis swainsonii), Natal francolin (Pternistis natalensis), southern red-billed hornbill (Tockus rufirostris), rock pigeon (Columba livia), white-necked raven (Corvus albicollis), leopard tortoise (Stigmochelys pardalis) and giant plated lizard (Gerrhosaurus validus).[50] In the Walter Sisulu National Botanical Garden of South Africa, the primary prey found around nests after a perceptible hyrax decline has become helmeted guineafowl and francolins, followed by cane rats, rabbits and dikdiks (Rhynchotragus ssp.).[62] Young baboons may also be hunted, even the large-bodied chacma baboons (Papio ursinus) which have issued a predator alarm call in response to the presence of Verreaux's eagles.[67] Carrion either fairly frequent or none at all.[2][56] A study of the taking of domestic lambs in the Karoo found only two cases of lambs being eaten by Verreaux's eagle and these were already dead when carried off. This contrasts with the golden eagle, which in some areas may eat many dead lambs and occasionally hunt lives ones.[3][68] Although any prey weighing over 4.5 kg (9.9 lb) is rarely taken, some ungulates hunted by Verreaux's eagles can be considerably larger.[15] Klipspringer (Oreotragus oreotragus) brought to the nest have weighed up to an estimated 12 kg (26 lb).[59] A Verreaux's eagle was observed to hunt and kill a mountain reedbuck lamb estimated to weigh 15 kg (33 lb).[69] The smallest known mammalian prey was a 97.6 g (3.44 oz) Cape gerbil (Gerbilliscus afra).[65][70]

Interspecies competition[edit]

A Verreaux's eagle finds itself attacked by a lanner falcon 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 wild predators are also attracted to 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.[15][23] Another case of kleptoparasitism by a Verreaux's eagle involved one stealing some carrion from a lammergeier (Gypaetus barbatus).[15] Verreaux's eagles occasionally prey on other large raptors including vultures, including white-headed vulture (Trigonoceps occipitalis), white-backed vulture (Gyps africanus) and Cape vulture (Gyps coprotheres), though the earlier cases probably refer to nestling or juvenile predation and the latter to nest defense on the part of the eagles.[49][63][71] An apparent predation attempt on a full grown juvenile Rüppell's griffon (Gyps rueppellii) was abortive.[72] 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.[73] 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).[23] Other predators of rock hyrax may include felids like African wildcats (Felis silvestris lybica), servals (Leptailurus serval), caracals (Caracal caracal) and leopards (Panthera pardus) as well as jackals (Canis ssp.), African rock pythons (Python sebae) and owls (mainly the large Verreaux's eagle-owl (Bubo lacteus) or possibly the Cape eagle-owl (B. capensis)). Neonate rock hyraxes may fall prey to mongooses and venomous snakes like Egyptian cobras (Naja haje) and puff adders (Bitis arietans).[74][75] 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).[76] 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.[77] 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.[9][78] This species is not normally aggressive to humans but may swoop uncomfortably close when the nest is being investigated.[9]

Behavior[edit]

Territoriality and movements[edit]

A rough estimated average of home range size in Verreaux's eagle is 10.9 km2 (4.2 sq mi).[23] Density of breeding pairs varies from 1 pair per 10.3 km2 (4.0 sq mi) in the Matobo Hills, Zimbabwe, 1 pair per 24 km2 (9.3 sq mi) in the Karoo, 1 pair per 25 km2 (9.7 sq mi) in East Africa, 1 pair per 28 km2 (11 sq mi) in the Bale Mountains of Ethiopia to a known maximum spacing of 1 pair per 35 to 65 km2 (14 to 25 sq mi) in the Magaliesberg and Drakensberg ranges.[2][49][79][80][81] 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.[82] While Matobo Hill home ranges ranged from 6 to 14 km2 (2.3 to 5.4 sq mi), most were observed to include about the same amount of kopje habitat (up to 5 km2 (1.9 sq mi)).[2] Populations fluctuate surprisingly little despite four-fold changes between peaks and troughs in hyrax numbers.[83] 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.[84] Some authors consider the Verreaux's eagle to be a partial migrant,[85] others describe it as sedentary.[86] 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.[2]

Verreaux's eagle displays may potentially occur almost throughout the year. Frequently displays are in response to the presence of another soaring pair or after repelling a single intruder from the territory. They will also display if anxious about the nest when humans or other large mammals approach too closely.[23] The male's display often consists of him first flying up in an undulating flight with wings readily held spread or closed. Then, once at a great height, he plunges down as far as 305 m (1,001 ft) at a time, then quickly rises back up, sometimes swinging to and fro like the arms of a pendulum, at other times diving and rising along a straight line. These evolutions may be embellished with somersaults and sideways rolls at the peak before the descent.[9][23] Some displays involve pairs of eagles. A pair frequently circles or makes figures of eight over their territory. One bird may roll over and present claws in flight or the male may fly behind female with exaggeratedly upcurved wings.[15] It is now the prevalent thought that most displays in Aquila eagles are territorial, as they often occur along the boundary of a given home range rather than near the nest.[3] Displays with talon-grappling and tumbling are often aerial fights between territorial birds and occasionally the eagles may clasp and whirl downwards (one such fight reportedly resulting in the birds plunging into the sea).[9][15]

Breeding[edit]

A breeding pair of Verreaux's eagles.

In Zimbabwe, 60 pairs may nest in 620 km2 (240 sq mi), equivalent to 1 pair per 10.3 km2 (4.0 sq mi), but this is exceptional. In East Africa, one pair nests each 25 km2 (9.7 sq mi) and in South Africa sometimes as little as 1 pair per 10.2 to 15 km2 (3.9 to 5.8 sq mi), but nearer 60 km2 (23 sq mi) being more typical.[15] Verreaux's eagle may build from 1 to 3 nests, sometimes none over the course of a year. In the Matobo Hills, the average number of nests built per pair is 1.4.[23] Eagles nesting in the Karoo have much larger territories, though are subject to persecution and habitat change, more so than many other populations.[23] In the Matobos, the species is near the breeding population capacity level with almost unlimited nests that are rather unevenly distributed among available jumbles of rocky kopjes. In Kenya, nests are more scattered and Verreaux's eagle sometimes do not breed even where the habitat seems appropriate and there are good numbers of rock hyrax.[9] By virtue of location on a narrow ledge, nests tend to be much broader than deep and a relatively small for the size of the eagle.[9] The flattish nests, made out of green branches and lined with green leaves, are up to 1.8 m (71 in) across and 2 m (6.6 ft) deep. Though a nest depth of around 0.6 m (2.0 ft) is typical, one old nest was 4.1 m (13 ft) deep.[9][15] Typically nests are on cliffs, often in an overhung crevice or in a small cave, sometimes on an open ledge. The nest site is generally marked by a 'whitewash' which is formed by the birds' droppings.[87] Verreaux's is the most cliff dependent of all eagle species, in the late 1970s only 3 known nests were in trees.[23] Very rarely, they may nest in trees, such as Euphorbia or Acacia, often those growing out of a cliff crevice.[15] A handful of nests in South Africa have even been on electric pylons.[88] 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.[9] It may take several hundred feet of rope for a human to reach the nest.[9] Predation of young in the nest is either suspected or anecdotely reported as having been committed by African rock pythons, baboons and caracals. However, predation is believed to be normally quite rare, due to the combination of factors such as the inaccessibility of most nests by foot (thus cutting off all but the most nimble mammalian carnivores) and the bold defenses of the parent eagles.[2] Verreaux's eagle have reportedly dropped sticks on potential nest predators. This has been considered a form of tool-use, which is generally unknown in other raptorial birds and has been mostly reported in corvids and herons.[89]

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.[15] In an unusual behaviour for eagles, the males may bring food to females before egg laying and, more typically, males bring almost all food during the incubation stage.[2] Two eggs are generally laid, though a range of one to three is known. The eggs are rather elongated ovals and being chalky white sometimes with a bluish tinge or a few reddish-brown marking, measuring from 71 to 83.4 mm (2.80 to 3.28 in) in length and 56–62 mm (2.2–2.4 in) in width, with an average of 76.9 mm × 58.6 mm (3.03 in × 2.31 in).[9] The eggs are laid at three-day intervals starting in the middle of the day. Both sexes incubate, but the female takes the major share and tends to sit all night over them. Sometimes, the male may sit for 40-50% of the day with more shifts for him towards the end of incubation. These are close-sitters, which are not easily disturbed off the nest.[9] Incubation is 43 to 47 days. Hatching happens at about to 2–3 days apart, with about 24 hours from the first chipping of the egg's surface to complete hatching. One egg is sometimes infertile and the second egg tends to be about 10% smaller.[9] The Verreaux's eagle is considered an “obligate cainist”, that is the older sibling normally kills the younger one (in more than 90% of observed nests), by either starvation or direct attack. Aggression may continue for up to 70 days after hatching.[2][90] 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.[9] 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.[90] 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.[90] 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.[3] In the Verreaux's eagle, no food is given to the hatchling in the first 36 hours, thereafter they are regularly fed.[2] 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.[9] 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.[23] The young Verreaux's eagle takes its first flight and then returns to the nest for the first fortnight.[9] 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.[9]

Population and status[edit]

A Verreaux's eagle at Giant's Castle.

Verreaux's eagles’ nests are estimated to have a 40–50% success rate per year.[9] Success of nesting is significantly higher when hyrax are common: 0.56 young per year dropped to 0.28 young per year. In fact, in poor food areas no breeding attempt commonly occurred (66% did not attempt to breed) whereas 24% did not attempt to breed in better food areas. Frequency of breeding attempts is lower in wetter years. Near 90% attempted nesting in years with 300 mm (12 in) of rainfall whereas 45% attempted during years with roughly 1,000 mm (39 in) rainfall.[84] In the Matobo Hills, persistent intrusion by an unmated adult into a pair's nesting territory seemed to have an adverse effect on nesting success.[91]

The estimated average lifespan is 16 years.[9] Verreaux's eagle has a total population estimated very roughly to be somewhere in the tens of thousands in total. In northeastern South Africa, the local breeding population is estimated to include 240 pairs, while the western Cape region of the country may hold possibly more than 2,000 pairs.[34][81] Verreaux's eagle lives in kopje habitat, which is generally non-vulnerable to human destruction, unlike, say, the savanna inhabited by martial eagles or the forests inhabited by crowned eagles.[15] Unlike the other two big African eagles, they do not often partake of much carrion, so are at little risk of poisoning from carcass left out to control jackals.[15] Nonetheless, some people shoot at or otherwise persecute them when given the opportunity due to the largely mistaken belief that they are a threat to small livestock.[68]

Perhaps the greatest concern for the species is when rock hyraxes are locally hunted by humans for food and skins, leading to likely declines and requiring the eagles to either switch to other prey or have their nesting attempts fail. In Walter Sisulu National Botanical Garden in South Africa, despite an appreciable decline in rock hyrax populations, breeding data revealed few changes in the incubation period, nestling period and post-fledging dispersal period in two known pairs of the eagles.[62] At this same site, despite it being one of the most popular nature areas in metropolitan Johannesburg, high levels of human activity have had no apparent adverse effect on the eagles’ breeding behaviour (by contrast, when exposed to similar levels of disturbance, golden eagles have been shown to temporarily abandon their nests).[3][92] 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).[15] 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.[92]

References[edit]

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  6. ^ Gargett, p. 30.
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  8. ^ a b c d Lerner, H.; Christidis, L.; Gamauf, A.; Griffiths, C.; Haring, E.; Huddleston, C.J.; Kabra, S.; Kocum, A.; Krosby, M.; Kvaløy, K.; Mindell, D.; Rasmussen, P.; Røv, N.; Wadleigh, R.; Wink, M.; Gjershaug, J.O. (2017). "Phylogeny and new taxonomy of the Booted Eagles (Accipitriformes: Aquilinae)". Zootaxa. 4216 (4): 301–320. doi:10.11646/zootaxa.4216.4.1.
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  13. ^ "Aquila morphnoides". The Peregrine Fund. Retrieved 22 April 2013.
  14. ^ "Aquila wahlbergi". The Peregrine Fund. Retrieved 22 April 2013.
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  16. ^ a b CRC Handbook of Avian Body Masses, 2nd Edition by John B. Dunning Jr. (Editor). CRC Press (2008), ISBN 978-1-4200-6444-5.
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  • 'Gordon Lindsay Maclean; 1993; Robert's Birds of Southern Africa; Sixth Edition; John Voelcker Bird Book Fund, p. 112-113
  • 'Alan and Meg Kemp; 2001; Birds of Prey of Africa and its Islands; SASOL, p. 78
  • 'Wonderboom Urban Verreaux's Eagle Project' http://www.blackeagleswb.com

External links[edit]

  • (Verreaux's eagle = ) Black eagle Aquila verreauxii - Species text in The Atlas of Southern African Birds