Tawny eagle

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Tawny eagle
From Etosha National Park
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Accipitriformes
Family: Accipitridae
Genus: Aquila
Species:
A. rapax
Binomial name
Aquila rapax
(Temminck, 1828)
Subspecies[2]
  • A. r. vindhiana – Franklin, 1831
  • A. r. belisarius – (Levaillant, J, 1850)
  • A. r. rapax – (Temminck, 1828)
Range of A. rapax
  Resident
Synonyms

Aquila rapax rapax

The tawny eagle (Aquila rapax) is a large

global warming, as well as persecution (largely via poisoning) and other anthropogenic mortality (largely through contact with various manmade objects) are driving the once numerous tawny eagle perhaps to the brink of extinction.[1][8][9]

Taxonomy

Dutch naturalist

Hieraeetus outside of Aquila. Furthermore, genetic research has further revealed a schism in superficially similar eagles between the tawny eagle and its close relatives and other superficially similar Aquila such as the golden eagle (Aquila chrysaetos) species complex. To date, the tawny eagle species group and golden eagle species group are still contained in the same genus despite the apparent lack of close relation.[3][16][17][18]

A tawny eagle sitting on the ground displaying typical features: a mid-sized eagle with a long neck, well-feathered legs, well-proportioned frame and large bill lacking a deep gape.

The tawny eagle was previously treated as conspecific with the migratory steppe eagle (Aquila nipalensis).[7][19] These eagles were considered part of the same species as recently as 1991.[20] The steppe and tawny eagles were split based on pronounced differences in morphology and anatomy. The steppe eagle is a larger bird, with a much more pronounced gape, and differs by appearance in its blockier frame, bigger wings and evinces different coloring at all stages of development, despite some morphs of the two eagles superficially resembling one another.[21][22][23][24][25] Furthermore, the respective species differ in ecology (dietary biology, nesting habits) and are strongly allopatric in their breeding ground distribution.[6][21] Two molecular studies, each based on a very small number of genes, indicate that the species are distinct, but disagree over how closely related they are.[26][27] Genetically, the tawny eagle may cluster more closely with the imperial eagle species complex despite the steppe eagle being more sympatric with those northerly Eurasian eagles.[3]

Subspecies

The distinctly darker subspecies native to India and elsewhere in Asia, A. r. vindhiana.

There are three described races of tawny eagles. The subspecific classification of the species has at times been considered complicated by variations and existence of different morphs; in turn they were once considered tentative.[4] However, each subspecies is largely allopatric in geography, the primary ambiguities lying in the northern part of east Africa where both African races may intergrade.[28]

  • A. r. rapax; distributed in Africa from the southern Democratic Republic of the Congo and central Kenya to all points southwards.[4] However, this race may range up to as far north as Ethiopia as well (thus likely intergrading considerably with the following subspecies which is widespread in Ethiopia).[29] Adult often of this nominate subspecies are often relatively more strongly rufous in colour than other races and are sometimes dark streaked below. Meanwhile, the juvenile tends to be light rufous. wing chord lengths in this race have been measured at 485 to 540 mm (19.1 to 21.3 in) in males and 509 to 565 mm (20.0 to 22.2 in) in females.[4] The mean wing chord length in two samples of A. r. rapax measured 501 and 512 mm (19.7 and 20.2 in) in males and 541 and 545 mm (21.3 and 21.5 in) in females.[7][30] The tail length of both sexes in A. r. rapax measures 245 to 295 mm (9.6 to 11.6 in) with a tarsus length of 79 to 92 mm (3.1 to 3.6 in). Body mass can range roughly from 1.6 to 3.1 kg (3.5 to 6.8 lb) in overall samples of at least 36 eagles.[4]
  • A. r. belisarius; this race resides in
    Arabia as well as far south as the northern Democratic Republic of the Congo and northern Kenya.[4][31] This race is described to appear "neater" than the nominate subspecies, possibly due to this race often occurring in even more desert-like conditions than the other races and thus having more compact feathering.[4][32] It is when compared to the nominate, often duller and browner above, showing less of a rufous tinge. Meanwhile, individual pale morph of A. r. belisarius often a shade or two darker than pale nominate but not consistently so. Although said to be slightly larger, measurement data shows this subspecies to of broadly very similar size to the nominate race. In males, the wing chord is 495 to 535 mm (19.5 to 21.1 in) and, in females, the wing chord is 500 to 562 mm (19.7 to 22.1 in).[4] The mean wing chord lengths were reportedly 515 mm (20.3 in) in males and 525 mm (20.7 in), which indicates a slightly less pronounced sexual dimorphism than in the nominate race.[7] As for body mass, 1 male was found to weigh 2 kg (4.4 lb) while three females weighed from 1.9 to 2.5 kg (4.2 to 5.5 lb).[4][7]
  • A. r. vindhiana; excluding the Arabian Peninsula, this race likely comprises all the tawny eagles found in Asia, such as in southeastern Iran and the Indian subcontinent.[6] However, ambiguities exists on where the range of A. r. belisarius ends and of vindhiana begins, especially in Middle Eastern areas.[33][34] Sometimes A. r. vindhiana is suggested as full species.[35] This subspecies averages darker than either other race and usually is lacking in warmer rufous tone. In general, it is somewhat more similar in hue to the steppe eagle.[4] Adult irises are sometimes brown in A. r. vindhiana (again reminiscent of the steppe eagle). The pale morph of this race is greyer and less rufous than African tawny eagles, although generally juveniles and immature are sometimes more rufous. It may be marginally the smallest subspecies, although in general the tawny eagle evinces remarkably little size variation across its wide range. Wing chord measurements are 473 to 535 mm (18.6 to 21.1 in) in males and 510 to 560 mm (20 to 22 in).[4][36][37] In males, the wing chord reportedly averages about 495 mm (19.5 in) and in females, it averages 525 mm (20.7 in).[7] In males the tail length is 242 to 258 mm (9.5 to 10.2 in) and in female it is 242 to 285 mm (9.5 to 11.2 in). The tarsus length of male A. r. vindhiana is 80 to 87 mm (3.1 to 3.4 in) and in females is 84 to 91 mm (3.3 to 3.6 in).[36][37] Unsexed adults in India weighed from 1.5 to 2.1 kg (3.3 to 4.6 lb).[6]

Description

Close-up showing gape extending only to below the middle of the eye

The tawny eagle is considered to appear "inelegant, scruffy-looking" but has a fairly characteristic aquiline silhouette.[4] The species has a fairly long neck and long deep bill with a gape line level with the eye, moderately long wings with fairly pronounced "fingers" and a slightly rounded to almost square-ended and shortish tail, which can be more reminiscent of the tail of a vulture than that of other eagles. The feathering on the legs is extensive and can appear almost baggy-looking.[4][12][38] The bill and head are strong and bold, the body well-proportioned and feet are powerful while the countenance is quite fierce-looking.[12] While perching, the tawny eagle tends to sit rather upright, often on stumps, posts, low trees or treetops for long periods of the day or may descend to the ground to walk somewhat unsteadily with a more horizontal posture. The wingtips when perched are roughly even with the tip of the tail.[4] Adults have variably colored eyes, ranging from yellow to pale brown to yellow brown, while those of juveniles are dark brown. Both the cere and feet are yellow at all ages.[4] The tawny eagle is polymorphic with considerable individual variation in plumage, resulting in occasional disparities in plumages that can engender confusion in some.[4][6] In adulthood, they can vary in coloration from all dark grey-brown to an occasionally streaky (or more plain) foxy-rufous to buffish-yellow.[4][39] Most adults are usually a general grey-brown or rufous-tawny color, with occasional pale spotting visible at close quarters on the nape and belly, coverts uniformly toned as the body.[6] The nape is consistently dark and uniform despite the feathers often being tipped paler with other feathers in adults, lacking the contrasting paler feathers often seen in other Aquila.[6] Females, in addition to being slightly larger, may tend to be slightly darker and more streaked than the males.[4] The most blackish-brown individuals tend to occur in India.[4][6] Adults often show relatively little varying colors apart from their somewhat blacker wing and tail feathers, though when freshly molted great wing coverts and secondaries may show small pale tips which may form pale lines along closed wing has tawny upper parts and blackish flight feathers and tail.[4] The head is often similarly tawny in colour as the body but may also sometimes shows darker eyebrows, other thin brown streaks or a darker chin.[4] Meanwhile, the tail is plain or obscurely dark barred (with around 7 subtle bands). The dark morph adult is essentially all dark, dull brown. Some dark morph tawny eagles with wear may show irregular streaking or molting browns and more blackish feathers.[4] Intermediate morph are dark to rufous brown above with the mantle and wing coverts variably streaked or molted lighter rufous as is the head with the crown or crown-sides being paler. The intermediate morph's underside is largely rufous (especially farther south in Africa) with breast and flanks very heavily and broadly streaked dark brown, though at times appears all dark brown contrasting with plain trousers and crissum.[4] Pale morph adult tawny eagles always show a clear contrast between the pale body and wing coverts which bear darker flight feathers and tail. In pale morphs, the underparts are rufous buff to lighty tawny-brown, phasing into somewhat darker lesser and median wing coverts to darker brown to even blackish greater coverts and flight feathers. The head may too be tawny in pale morph tawny eagles but sometimes with thin brown streaks or darker chin. Below pale morph adults are all light rufous to tawny buff or brown, sometimes paler below the belly area. In worn individuals the bodily feathers of pale morph tawny eagles can appear almost whitish.[4] Dark morph juvenile tawny eagles are generally light rufous to rufous brown with creamier lower back to upper tail coverts. Juveniles show thinly pale-tipped dark brown greater coverts and remiges while the tail is barred grey and brown usually with a narrow creamy tip. Dark morph juveniles may fade to pale buff or creamy often before molting into browner plumage. Subsequent stages are not as well-known but it appears dark morph subadults gradually manifest a darker brown or rufous brown color on the mantle, as well as on the head and upper breast while maintaining a buffish rear body (i.e. lower back and rump patch). Generally other morphs are similar but not as well-known and are perhaps individually inconsistent. Many are rufous or sandy after a molt but have mottling later on, the extent of pale feathers indicative perhaps of their ultimate adult morph.[4]

A streaked morph of the nominate subspecies of tawny eagle.

In flight, the tawny eagle appears as a large raptor with a noticeably protruding head on a long neck, with a deep chest, long and broad wings with a somewhat narrower seven-fingered hand.[4] The trailing edge of the wing is slightly curved outwards, indenting at the junction of primaries and secondaries, whilst the rounded, medium-length tail is usually held spread.[12] The deep beats of the kinked wings can make their flight appear rather heavy and slow but they are quicker and more expansive in wing movements and often less forceful-looking than larger Aquila like steppe eagles and can be very agile when chasing other raptors to rob them.[4][6] Tawny eagles soar with flat wings or very slightly raised and hands only slightly lower, and may fly similarly in a glide but may too arch when in a fast glide.[4] Adult dark morphs are more or less uniform dark brown above and below, showing indistinctly and slightly paler and greyish primaries on both sides. Above, the main contrast on dark morphs above is paler creamy rump patch while, on the underside, the greyish color is contrasted with blackish tips and a diffused trailing edge along both the wings and tail. Intermediate morph tawny eagles are variably rufous streaked on brown to rufous brown on the back and wing coverts with a similar contrasting pale rump above as dark morphs. Below the intermediate's heavy dark streaks are only subtly different and their coloring can appear almost uniform. The wing quills of intermediate morphs are often greyer with a stronger contrast of the paler inner primaries and blackish wing ends. Pale morph are all pale tawny or buffish on both sides of the wing, which contrasting strongly with demarcated dark brown about the greater coverts, flight feathers and tail and usually the scapulars. The primaries are quite pale on pale morphs with sometimes the hint of a pale carpal comma. Some pale adults have pale bases to all the underprimaries and the quills are sometimes unbarred, but more usually the feathers have dense but narrow dark bars.[4][6] Dark morph juveniles are light rufous to pale tawny body above which contrasts strongly with dark brown greater coverts, rear scapulars, flight feathers and tail, in turn all highlighting the creamy lower back to tail coverts. Below dark morph juveniles can look similar to pale morph adults apart from trailing whitish edges and often irregular pale diagonals along tips of greater wing coverts, though usually these fade early on. Little is known plumage development but the young eagles moult into brown, becoming patchy with intermediate often showing 1-3 darker bars on wing linings.[4] The underparts of subadults (i.e. around 2 to 3 years or old) are typically two-toned, with darker brown about the breasts, belly and underwings coverts while the remainder of the underbody is creamy light in colour. This two-toned pattern is evinced in subadult tawny eagles both from India and Africa.[6][40] Adult plumage is obtained between the 4th and 5th years of life.[4]

Size

A richly rufous-colored tawny eagle.

This is a large bird of prey, though is medium-sized for an

Aquila. Among currently accepted species in the genus, it is of quite similar size to Bonelli's eagles (Aquila fasciata) (though is notably longer winged), slightly larger than African hawk-eagles (Aquila spilogaster) and much larger than Cassin's hawk-eagles (Aquila africanus). Otherwise, females of the larger species of Aquila are frequently around twice as heavy as an average tawny eagle.[41] As is typical in birds of prey, the female tawny eagle is larger than the male, though relatively modestly so and a difference between the sexes is typically up to 15%.[4] In total length, tawny eagles can measure from 58 to 75 cm (23 to 30 in).[6][42] A typical length for a tawny eagle is considered about 65 cm (26 in).[43] Wingspans can measure from 157 to 190 cm (5 ft 2 in to 6 ft 3 in). Weight can range in fully grown birds from 1.5 to 3.1 kg (3.3 to 6.8 lb).[4][6][44] Average weights were reported in one study as 1.91 kg (4.2 lb) in 5 males and 1.97 kg (4.3 lb) in 5 females.[30] In another study, 10 unsexed adult tawny eagles were found to have weighed 2.5 kg (5.5 lb) on average while, for the same data pool, a sample of 15 had an average wingspan of 182.9 cm (6 ft 0 in).[45] Another small sample of African males, sample size four, averaged 1.85 kg (4.1 lb) while three females averaged 2.28 kg (5.0 lb).[7] The mean mass of the species in one estimate was 2.3 kg (5.1 lb).[46] In all standard measurements combined, the wing chord can vary from 473 to 565 mm (18.6 to 22.2 in), the tail from 242 to 295 mm (9.5 to 11.6 in) and the tarsus from 79 to 92 mm (3.1 to 3.6 in).[4][47] The culmen length of Kenyan tawny eagles was measured at 33.3 to 42.4 mm (1.31 to 1.67 in), averaging 37.7 mm (1.48 in), while the gape width is 44 mm (1.7 in) on average, ranging from 40.3 to 49.9 mm (1.59 to 1.96 in).[21][48] The hallux-claw, the enlarged rear talon often used as a killing instrument on accipitrids, can measure from 27 to 37.7 mm (1.06 to 1.48 in), averaging 31.8 mm (1.25 in) in one sample and 32.3 mm (1.27 in) in another. The talon size is not especially large for a booted eagle and is proportionately similar in size to those of steppe eagles and eastern imperial eagles (Aquila heliaca).[7][21][48]

Confusion species

The slightly darker northern and central African subspecies, A. r. belisarius, in flight displaying the species typical flight profile.

The tawny eagle lives in multiple areas where other broadly similar brownish hued and largish raptors often occur. Thus identification is seldom straightforward.[49][50]

One source that can especially engender potential confusion in its wintering range is the formerly conspecific steppe eagle. The steppe is larger with a shorter neck, relatively longer and narrower wings, a more massive beak, particularly via the exceptional depth of the gape (although in flight can appear smaller headed due its less protruding neck) and has a longer and rounder tail. Furthermore, steppe eagles tends to have much bolder and widely spaced barring on the wings than tawny eagles and more distinct dark trailing wing edges and paler throats.[4][21][50][39][51]

Beyond steppe eagles, comparisons to various other groups of sympatric booted eagles may be made. Compared to the

Palearctic breeding eagle who often winters in the resident range of tawny eagles, is fairly similar, but that species has a relatively shorter and broader tail, less baggy feathers on the legs and usually a rather darker and more uniform adult plumage.[4] The fulvescens form of the greater spotted eagle must be distinguished from the pale forms of the tawny eagle by its underwing pattern, often with completely blackish underwing coverts and usually plain looking dark remiges over the entire primaries with more distinct pale carpal arcs.[4][52] The likewise migratory lesser spotted eagle (Clanga pomarina) is smaller than the tawny eagle and more compact with a distinct white U above the tail.[4][52] The residential African Wahlberg's eagle (Hieraeetus wahlbergi) can have a similar uniform plumage as in tawny eagles but always has greyer flight feathers and is much smaller than tawny eagles with relatively longer and more rectangular wings and a longer, narrower and straighter-tipped tail.[4][52] The eastern imperial eagle in juvenile plumage can appear similar to the pale and intermediate morph tawny eagles, but the imperial eagle is usually visibly larger, with slenderer, longer wings, a longer, broader tail as well as having dark brown streaking on the chest, mantle and wing coverts and bearing more distinct pale trailing edges and wing bars.[4][39]

Dark-morph tawny eagles in India may be distinguished from similarly sized

black-breasted snake eagles (Circaetus pectoralis) and juvenile bateleurs (Terathopius ecaudatus), are sometimes mentioned as a potential source of confusion but are usually rather distinct (all larger headed, rather smaller billed, shorter tailed and bare legged with often less uniform coloring) even in their most similar hues.[12][52]

Calls

Tawny eagles are generally silent in most of their range.[4] However, unlike steppe eagles, which are almost always silent away from their breeding grounds, they are said to occasionally vocalize in any season.[39] They are also more vocal when not breeding than the spotted eagles.[4] The usual call is a harsh, hollow-sounding, loud bark, variously transcribed as kowk-kowk, kau-kau, kiok-kiok or ki-ark. The call is fairly high-pitched (slightly less deep than the steppe eagle's when the latter is breeding) but is still deeper voiced than spotted eagles.[4] In Kruger National Park it is said the call is loud and far-travelling.[12] Male tawny eagles are the most frequent vocalizers in the species, particularly during sky-dances, but also in other contexts. These include but are not limited to food arguments, disturbances during nesting and males attracting females for food passes.[4] In nine years of monitoring tawny eagles in Zimbabwe, however, the call was not heard once.[53] Its silence there may be due to the flat landscape.[53] Other call recorded include a harsh grating k eke ke... in aerial courtship displays and a throaty kra in kleptoparastic pursuits. A kra-kra call may emitted at times to warn intruders.[4][6] The female may also emit an occasional mewing, high shreep-shreep at the nest as well as a rare raucous scream (possible food-begging and alarm calls, respectively).[4][6][54] The young chick tawny eagle chips initially but once its feathers emerge, it tends to beg with a loud call, i.e. we-yik, wee-yik.[12]

Distribution and habitat

Tawny eagles have an extremely extensive natural distribution. The African population can be found in three, fairly discrete populations.

Gambia, Togo, Nigeria and (though possibly not breeding) in Ivory Coast and Ghana.[61][62][63][64][65][66][67] In east Africa and central Africa, the tawny eagle is found in central and eastern Democratic Republic of the Congo and throughout the drier portions of Uganda and in the entire nations of Kenya, Tanzania, Zambia (quite often residing in the Luangwa valley and the Chambeshi drainage), Malawi and Mozambique. In east Africa, it is considered perhaps the most widely distributed and regularly sighted brown eagle.[68][69][70][71] In southern Africa, the tawny eagle is found throughout Zimbabwe (now often rare apart from Matabeleland and Chipinga Uplands), Botswana (still regular in Okavango Delta) and some areas of Namibia, southern and western Angola (Cuando Cubango, Cunene, Huíla Namibe, to Malanje), Eswatini, Lesotho and northern and central parts of South Africa, i.e. mainly north of the Orange River but sometimes down to the Cape Province.[1][12][72][73][74][75][76][77][78][79] The tawny eagle may be extinct as a breeder in Eswatini where it was last confirmed to have bred in 2001.[80]

A tawny eagle perched in Rajasthan in India.

Out of Africa, the species may possibly be found in the southwestern part of the

'Asir Regions, but few to none confirmed breeding events have been reported in the last few decades.[1][81][82] The tawny eagle is considered a rare vagrant in Israel, though some are verified, other reports of them often turn out to be misidentified steppe eagles.[83] They are also known as a rare vagrant in Oman.[84] In Asia, the tawny eagle exists in isolation in southeastern Iran (as in Arabia, verified recent breeding is not known) and somewhat more continuously in eastern Pakistan (often in the Indus valley), much of north and peninsular India, eastward scarcely through southern Nepal and Assam.[4][85][86][87] Though Nepali tawny eagles are rarely recorded, it is thought that the species still resides there in lowland semi-deserts.[88] The Indian range is from Punjab through the Indo-Gangetic Plain and western Bengal, northeastern Bihar, the Deccan Plateau with range continuing down to Andhra Pradesh, Karnataka and (mainly north-central) Tamil Nadu.[6][85][89] Records of vagrating tawny eagles turning up in Myanmar, northern Vietnam and Thailand are thought to have been likely misidentified steppe eagles or are based on now unidentifiable specimens.[90] A small handful of vagrants have been verified to turn up in Sri Lanka (the only known appearance by an Aquila eagle there).[91] Old reports of vagrancy, probably in need of confirmation, are known also from Afghanistan.[85]

Habitat

Tawny eagles are often at home in the arid and yet rich bushveld.

Tawny eagles occurs in fairly open country at varied elevations but usually live in

forest-savanna mosaics but can move into dry woodlands and semi-deserts when not breeding.[4] In Morocco, the species prefers forested areas near mountains with adjacent plains. Elsewhere in Africa, tawny eagles typically inhabit wooded savanna such as dry Acacia savanna and semi-desert to desert areas. However, extreme desert areas, completely lacking in arborescent growth, are avoided nearly as much so as humid tropical rainforests. It also occurs at times in manmade areas such as arable lands, roadsides, dams, farmland, cattle pastures and game areas if feeding opportunities occur in them.[4][29][71][75][76][92] In southern Africa, thornveld is often the preferred habitat with the tawny eagles mostly preferring stands of Acacia. Despite similar climates, within the miombo woodland, the tawny eagle tends to be more scarce.[12][71][75] In India, similar habitats may largely be used but the tawny eagle may fairly often occur too in the vicinity of villages and cultivations and frequents garbage dumps and slaughterhouses somewhat more so than they do in Africa.[4][6][85] In addition to all gradients of arid zones, in India, the tawny eagle frequently is found around thorn forests.[6] Tawny eagles may live from sea level to about 3,000 m (9,800 ft) but tends to prefer somewhat lower elevations.[4] Despite a certain level of aridity expected in tawny eagle habitats, they normally will not nest unless a habitat meets certain demands.[5] The tawny eagle's presence is predicated on the availability of ephemeral rainfall during the wet season.[5][93][94] This reliance on some rainfall is probably key to habitat quality and resulting prey populations to some extent, but also to the availability of nesting sites.[12][93] The tawny eagle is by and large an obligate tree nester and so areas that become too arid to support tree growth or where trees are overharvested are unlikely to retain the species.[6][12][95]

Behaviour

A tawny eagle in flight.

The tawny eagle, quite unlike the steppe eagle, is largely sedentary and

flock at opportunistic feeding sources, the tawny eagle is usually considered solitary.[4][6] However, groups of two to three tawny eagles are sometimes seen, such as in the Indian subcontinent, but occasionally group sizes may even exceed this figure.[6] In the Mirpur Division of Azad Kashmir in Pakistan, small flocks of tawny eagles have reportedly been witnessed gathering in warmer spots between November and February, over three years of study.[104] Small groups or aggregations are known to occur in Africa as well near concentrated foods and even communal roost have been reported in trees, power pylons or on the ground.[4] Like many large raptors, the tawny eagle probably spends the majority of its day perched but take wing a few times a day.[6][12] Unlike most large eagles, in India at least, tawny eagles are often fairly accustomed to humans and may allow fairly close approach by observers.[6][105]

Feeding

With a black-backed jackal, road traffic victim in Ethiopia.

The tawny eagle is unique as an Aquila eagle in the lack of apparent specialization in its feeding behaviour.

springhares have been preyed upon by tawny eagles in areas where there was no possibility they were killed by traffic at night. In addition to other observations have been made where tawny eagles drink and bathe at night, some nocturnal subsistence behaviour by this species has been inferred but no irrefutable evidence has been brought forth either.[12][107] Semi-regular attendance at grassfires in India, presumably in order to capture displaced creatures, has been reported.[85] More than 200 species, including both live prey and carrion, are known to be eaten by tawny eagles and they may have one of the most variable diet of all tropical eagles.[6][12][48][53][108][109] Reportedly, most prey the tawny eagle will take alive will weigh not less than 125 g (4.4 oz) and not more than 2.5 kg (5.5 lb), however live prey has been revealed to be regularly more variable than even that estimate represents.[4][12][48][53] One compilation study showed that, compared to 8 other Aquila and spotted eagles, the tawny eagle's diet was the most evenly spread across all weight classes of prey from under 63 g (2.2 oz) to over 4 kg (8.8 lb), though took prey in the latter prey class slightly less so than the much larger golden and wedge-tailed eagles (Aquila audax). This study further determine that the most often focused on weight class in tawny eagle's diets were 0.5 to 1 kg (1.1 to 2.2 lb) and 1 to 2 kg (2.2 to 4.4 lb) prey class, accounting for a little less than half of the prey by quantity.[18] According to this authority, the mean prey size falls around approximately 921 g (2.030 lb), which is around 5 times greater than the mean estimated prey size for the steppe eagle species, around 38% greater than mean estimated prey size of imperial eagles and considerably less only than the golden, wedge-tailed and Verreaux's eagles among the 8 studied Aquila and Clanga species.[18]

Probable live prey

A tawny eagle with its prey, a rock monitor.

Determining whether prey has been taken alive at the nests of tawny eagles is generally considered to be difficult, although observations suggest that during breeding tawny eagles usually deliver fresh prey while raising young, indicating that such prey are usually either taken alive or newly pirated from other predators.

Timbavati and Klaserie, 63% of the diet was birds, 34% of it was mammals and 3% were reptiles. At Highveld, 25% of the diet consisted of yellow mongoose (Cynictis penicillata), 15% Cape ground squirrels (Xerus inauris) and 13% helmeted guineafowl. At Timbavati and Klaserie, various francolins were strongly predominant in foods, at about 44% with another 17% by various mongooses.[110][111]

Out of the southern and eastern areas of Africa, less quantitative analysis has been undertaken into the feeding habits of tawny eagles, even around nests. What is known of their prey elsewhere is mainly from wide-ranging surveys, secondary accounts and photographs.

Patas monkeys (Erythrocebus patas), grivets (Chlorocebus aethiops) and vervet monkeys (Chlorocebus pygerythrus) up to the size of juveniles of several species of baboon.[48][118][125][126][127] However, unlike with larger eagles, the troops of certain baboons do not seem to regard tawny eagles as a threat based on their behavioural responses.[128] While most ungulate prey other than dik-diks is probably largely scavenged as carrion or stolen from other predators, the small calves of ungulates such as Thomson's gazelle (Eudorcas thomsonii) are sometimes apparently killed by tawny eagles.[129] A general picture appears to emerge that tawny eagles quite often takes relatively large mammalian prey, surprisingly often creatures weighing up to 3 to 4 kg (6.6 to 8.8 lb) such as hares, dik-diks, the young of other antelopes, hyraxes and so on.[12][21][53][130]

A tawny eagle is mobbed by a blacksmith lapwing; these eagles are a potential menace to many different kinds of birds.

While mammals prey varies from rodents to hares, mongooses and small antelopes, the diversity and size range of bird taken may be even more impressive and more than 120 avian prey species have been reported in the prey spectrum.

pigeons,[12][36][132] mostly medium-sized species of bustard and hornbill[47][48][36][110][133][134] and numerous water birds from small coursers, lapwings, rails and grebes to large flamingoes, storks and herons both small and large.[12][48][110] Both young and adult Old World flamingoes of both African species are known to be attacked on occasion, as well as white-breasted cormorants (Phalacrocorax lucidus) and great cormorants (Phalacrocorax carbo), all birds similar in size or somewhat heavier than the tawny eagle itself.[135][136][137] Further impressive water bird prey includes reportedly spur-winged goose (Plectropterus gambensis), which weighs about twice as much as tawny eagle.[53] Even larger avian prey are taken including a common crane (Grus grus) killed by a pair in Saurashtra (although it was an injured one) and presumably adult female Kori bustard (Ardeotis kori). If average-sized, these prey items likely weighed more than 5 kg (11 lb).[114][41][138] More minor avian prey includes nightjars, coucals, sandgrouse, swifts, bee-eaters, kingfishers, rollers, wood hoopoes, turacos, parrots and several passerines.[6][12][36][48][110][139][140][141][142] One small passerine the tawny eagle may routinely hunt is the super-abundant red-billed quelea (Quelea quelea).[143] Near poultry farms, tawny eagles can take to not infrequently lifting free-range chickens (Gallus gallus domesticus) and other poultry, especially when the eagles must feed their young, thus in turn potentially drawing ire of local farmers.[6][12][38][144]

Various snakes are taken opportunistically by tawny eagles and they can be quite bold about hunting

African rock python (Python sebae), speckled sand racer (Psammophis punctulatus), rufous beaked snake (Rhamphiophis oxyrhynchus), black-necked spitting cobra (Naja nigricollis), black mamba (Dendroaspis polylepis), boomslang (Dispholidus typus) and puff adder (Bitis arietans).[12][48][146] They also hunt lizards not infrequently given the chance, usually favoring fairly large species but capable of taking those ranging from geckos to rock monitors (Varanus albigularis).[12][36] At one nest in Zimbabwe, monitor lizards made up 29% of 83 prey items, but they were only 8% of 107 prey items of 3 other nests in the same park.[53] One of the most frequently seen prey to be taken by tawny eagles in India have been Indian spiny-tailed lizard (Saara hardwickii).[6][147][148] More minor prey have included turtles, frogs and toads and fish. A tawny eagle in southern Africa was seen to wade into shallow water and successfully pull out a largish catfish.[12][108][110][149] Tawny eagles can also take communal nesting and swarming insects fairly frequently. These are generally termites, which can attract several of these eagles especially amongst non-breeding eagles and young ones. When visiting termites, the tawny eagles commonly eat alates and may, with an unusual lack of aggression, share the food source with several other birds of prey, including as many as a half dozen conspecifics.[150][151] At times, tawny eagles can also be attracted to swarms of grasshoppers.[152] In one case, a tawny eagle was seen consuming the fruit of an Adansonia tree, an unusual instance of frugivory which is very rare in accipitrids other than one unusual species: the palm-nut vulture (Gypohierax angolensis).[12] A tawny eagle was once witnessed picking through elephant dung along with a vulture, presumably searching for dung beetles to consume.[153]

Carrion

A tawny eagle perched amongst white-backed vultures, with which they are often obligated to share carrion in Africa.

Although the tawny eagle does hunt for food, it also relies extensively on

Rüppell's griffon (Gyps rueppellii), followed by all other vultures with the tawny eagle and the bateleur in the second most and the most subordinate scavenger positions.[160] Similar scavenger hierarchies have been reported elsewhere as well.[156][157] Bateleurs were the most likely to first find a carcass of the Maasai Mara scavengers and both the tawny and bateleur were considered as scavengers with "low competitive ability and high search efficiency".[160]

However, tawny eagles will at times be able to displace the smaller species of vulture such as hooded vultures (Necrosyrtes monachus) and Egyptian vultures (Neophron percnopterus), both of which are similar in weight to the tawny eagles themselves, with one tawny eagle even reportedly keeping as many as 20 vultures at bay at a carcass. In general, based on the literature, such an event of aggressiveness by this species at a large carcass would surely be unusual.[12][53][160][161] Tawny eagles do tend to be dominant over bateleur at carcasses, however.[12] Gyps or griffon vultures are usually the most numerous vultures in attendance at carrion and are considerably larger than tawny eagles but sometimes may briefly tolerate a tawny eagle to feed in their midst depending on the circumstances.[12][162][154] Usually, the larger the group is of griffon vultures, the less likely the tawny eagle is to get to feed.[46][160][162][154] The eagles not infrequently remain on the periphery of the vulture feeding frenzy and wait for pieces of flesh to appear. Often they will be able to pick up small scraps but will wait until the carcass is finished and few vultures remain to feed. The tawny eagle can benefit from leading other scavengers to carrion or feeding subsequently to them since, unlike the largest and most aggressive vultures, such as lappet-faced vultures and cinereous vultures (Aegypius monachus), the tawny eagle cannot tear open large carcasses on their own and tend rely on another source to access any bits of the nutritious viscera.[6][12][46][53][156][162] The tawny eagles when finding an unopened large carcass have few feeding options although may eat the eyes in such circumstances, as was verified in the circumstance of a tawny eagle finding a horse (Equus ferus caballus) carcass offered by researchers.[159] Roadkills are another feeding option as they are often torn asunder by impact with automobiles and the eagle may be able to (at least briefly) monopolize the carcass.[6][12][28] Perhaps not coincidentally, in Maasai Mara, the tawny eagles were found to benefit from a carcass being nearer human habitations and in lower quality habitats relative to the other scavengers.[160] In particularly in India, scavenging tawny eagles tend to regularly occur at landfills where vultures seldom come but wintering steppe eagles may often feed alongside them seasonally.[6][36] Garbage dumps are also visited in different parts of Africa such as Uganda and Ethiopia by hungry tawny eagles.[163][164] Semi-predaceous and aggressively disposed vultures, like white-headed vultures (Trigonoceps occipitalis) in Africa and red-headed vultures (Sacrogyps calvus) in India as well as the lappet-faced and cinereous vultures, tend to have little tolerance for tawny eagles, with the latter unlikely to approach until these aggressive vultures have had their fill.[6][12][53][165] On the contrary, though, at times white-headed vultures and tawny eagles have been observed peaceably sharing roadkills in some instances.[12] Often tawny eagles will come to smaller carcasses of almost any animal, as will other smaller scavengers like bateleurs and hooded vultures as well as crows, perhaps merely to avoid the competition that often occurs at large carcasses.[6][46][156][159][160] One subadult tawny eagle was observed to be following a pack of African wild dogs (Lycaon pictus), almost certainly in order to scavenge off of their kills.[166]

Kleptoparasitism

A tawny eagle perched with a young bateleur. The ecology of these species is often broadly similar but the tawny eagle usually dominates the bateleur in food competition.

The tawny eagle steals food from other raptors in addition to catching its own prey and coming to previously dead food sources.

Robber Eagle".[8] This behaviour is not entirely segregated from their scavenging on carrion behaviours but the considerable aggressiveness and boldness of the eagles in this circumstances are very different from their rather retiring disposition in scavenging contexts.[12][53][167] At times the tawny eagle is considered "fearless" in their piratical attacks and is certain to engage in them more frequently than almost any other member of the booted eagle clan or perhaps even birds of prey.[7][12] Other related eagles like the steppe eagle and eastern imperial eagle, as well as most sea eagles, can be locally regular kleptoparasites but tawny eagles rob prey from other birds with some regularity in every part of the range.[6][12][47] Amongst all birds, only a few types of seabird such as skuas and frigatebirds are likely to derive a majority of their subsistence from kleptoparasitism.[168][169] Generally, tawny eagles will surprise other birds of prey with a dashing stoop and yank away the prey item in a manner of seconds; they will seldom completely land if the prey item is intercepted on the ground so they can take off with the plundered item quickly.[12][53][146] The size of birds that the tawny eagles have been known to pirate food away from have ranged from species as small as black-winged kites (Elanus caeruleus) and common kestrels (Falco tinnunculus) to those as large as a lammergeier (Gypaetus barbatus).[7] There seems to few limits to the raptorial birds that the tawny eagle will not pirate from given the opportunity.[12][47] In one case, a pair of tawny eagles descended on a secretarybird (Sagittarius serpentarius) that had killed a large puff adder and displaced both the secretarybird and an African harrier-hawk (Polyboroides typus) that had tried to enter the fray, after which the eagle pair split the adder between them.[113] Other raptors known to be attacked for piracy in well-known and often repeated instances have included dark chanting goshawks (Melierax metabates), bateleurs, lanner falcons (Falco biarmicus) and even the imposing martial eagles (Polemaetus bellicosus) and Verreaux's eagles, the latter eagles having appeared to offer surprisingly little to no contest the tawny eagle's piracy despite their great strength and formidable talons.[12][53][170][171] Carnivorous birds that are not traditionally considered raptorial birds, such as marabou storks and southern ground hornbills (Bucorvus leadbeateri), are also occasionally kleptoparasitized by tawny eagles.[12][172][173] Interspecific piracy may be most frequent on bateleur despite that species being similarly sized and powered as the tawny eagle. While 5 displacements of tawny eagles by bateleur were reported in a study on their interactions, 26 instances of tawny eagles displacing bateleurs were described, clearly far more.[174] Several smaller birds of prey were observed to be repeatedly robbed of their catches at a red-billed quelea colony, including queleas crippled but not killed by lanner falcons, although some of the maimed queleas were contested by jackals as well.[12][53]

On occasion, a tawny eagle will find itself on the losing end of a kleptoparasitic interaction. Somewhat larger eagles have been seen to displace tawny eagles off of prey. These include

Ethiopian wolves (Canis simensis) were seen to rob tawny eagles repeatedly of freshly-caught rodents, succeeding in 5 of 21 attempts to do so.[178] Even much smaller birds such as house crows (Corvus splendens) have been seen to successfully rob a tawny eagle of its prey.[179]

Interspecific predatory relationship

A tawny eagle in India flies with two black kites.

The tawny eagle occurrence in Africa and the Indian subcontinent places it in arguably two of the most competitive environments for birds of prey in the world.

snake eagles, will use old nests built by tawny eagles.[12] Although the habitats used by martial and tawny eagles have been reported as broadly similar, detailed study in the Karoo found that the tawny species preferred areas with higher and more predictable summer rainfall and with higher primary productivity than the martial.[182]

Opportunistically, the tawny eagle may prey upon smaller birds of prey but this is fairly infrequent and the capture of raptorial birds has thus far been seldom reported. A hungry or food-gathering male tawny eagle may infrequently plunder the nests of other raptorial birds.

corvids, snakes and carnivores capable of climbing.[4][53][108] One confirmed predator of nestling tawny eagles is the honey badger (Mellivora capensis).[185]

Breeding biology

Pairing and Territories

The tawny eagle often seems to pair for life. Like most birds of prey, they are quite territorial towards conspecifics.[4][12] The commonest display is single or mutual high circling or soaring often in wide spiral. Males will sometimes dive and stoop repeatedly around the female, though she does not usually respond by turning over.[4] Pairs may engage in the display each year to strengthen pair bonds.[6] Occasionally two tawny eagles will interlocks talons to descend rapidly, cartwheeling down 30 m or more within a few seconds, sometimes disengaging just before the ground.[6] In other related eagles of the Aquilinae subfamily, cartwheeling interactions are usually considered to be aggressive fights between a territorial eagle and an intruder of the same gender. Prior studies thought this to be the case for the tawny eagle, with an estimated 82% of cartwheeling instances thought to be aggressive, 11% for courtship and 7% for apparent play. However, through closer observations evidence has been made of frequent cartwheeling between males and females as a regular part of the courtship display.[186][187][188] Undulating sky dances are sometimes performed too by males with a series of descents and upward swoops on partially close wings, accompanied by calling. However, instances of this seem to be rare.[4] In one instance, two males appeared to engage in a display for a single female.[114] Per one author's opinion the aerial displays of the tawny eagle are "not particularly spectacular compared to other eagles".[12] The breeding season tends to fall in March to August in northeastern Africa, October to June in west Africa and in almost all months of the year but in central, east and southern Africa, but mainly from May to November in Kenya and April to January in central and southern Africa.[4][189] In India, the breeding season is usually November to May, but occasionally can vary from any time from October to August.[4][6] Mating generally occurs in and around the nest vicinity.[6] The density very variable on the African continent overall of breeding pair which were estimated to occupy about 75 to 300 km2 (29 to 116 sq mi) each.[4] Zimbabwe nest spacing was found to be 7 to 10 km (4.3 to 6.2 mi) in one study. On the border of Kruger National Park, 7 pairs found in a 460 km2 (180 sq mi) area but in regular spaced pylon nests in western Transvaal, nests were 19 to 20 km (12 to 12 mi) apart.[12] In Hwange National Park, over 11 years of study, 92 pairs on were found to be nesting over basalt in a 4,724 km2 (1,824 sq mi) area while 84 pairs on Kalahari sands in a 9,876 km2 (3,813 sq mi) area. Mean nest distances on basalt were around 4 km (2.5 mi) while on sands it was around 59 km (37 mi).[5] In Zambia, the nesting density was considered high for the species at a pair per 28 km2 (11 sq mi).[108]

Nest

The nests of the tawny eagle are large platforms, composed of sticks but sometimes incorporating animal bones.

transmission towers.[191] Populations of large eagles like the martial eagle and Verreaux's eagle have been recorded breeding on these power pylons since the 1970s.[191] Between 2002 and 2003, 39% of electrical faults recorded on transmission lines were due to large eagle nests.[191] As a result, problem nests were dismantled and rebuilt below the electrical conductors.[191]

Eggs

MHNT
MHNT

Eggs are laid at intervals of several days, mainly timed to the dry season but at times also in the wet season.

Kutch and Jaisalmer, the young are already leaving the nests.[6] Clutch sizes range from 1 to 3 eggs per nest, but average 1.7 eggs per clutch.[12][108] In drier years in Hwange National Park, clutch sizes appear to become reduced.[5] The eggs are white but variously and usually faintly marked with brown, varying from unmarked sometimes to quite well-marked with spots and blotches of reddish brown.[7] In 67 eggs of the nominate subspecies, the eggs were 64 to 75.7 mm (2.52 to 2.98 in) in height by 49.9 to 60 mm (1.96 to 2.36 in) in diameter, with an average of 69.6 mm × 54.8 mm (2.74 in × 2.16 in) in the sample while another 30 from the same race averaged 71.5 mm × 56.3 mm (2.81 in × 2.22 in). In A. r. vindhiana, 80 eggs measured from 58 to 75.1 mm (2.28 to 2.96 in) by 46.4 to 57.6 mm (1.83 to 2.27 in), with an average of 66 mm × 52.8 mm (2.60 in × 2.08 in).[7][12]

Development of young and parental behaviour

Eggs are

fledging the nest fully after 10–12 weeks.[4][53] However, the female may remain to shelter during rainstorms around to as late as the fledging stage.[4] The full stage of dependence is ongoing for about 6 weeks after fledging. The young tawny eagle may stay with the parents even until next breeding season.[4] In India at least, after the nesting period, the pairs disperse and leave the nesting area, seldom being seen near the nest until pairing off again initiates in October.[6] A juvenile tawny eagle that was shot at 2 years old was 48 km (30 mi) away from its original nest while 2 juveniles at 5 months and 7 months old were 50 and 34 km (31 and 21 mi) away, respectively.[12]

Nesting success and failures

Nest losses of eggs and young appears to be quite high.[4] Young eaglets often die, at times by their siblings, and if poorly guarded nests are often predated by a probably wide range of predators.[4] Nesting success is driven by quality of habitats and food access.[6] Breeding efforts in Zimbabwe produced 19 young in 26 pair years with a replacement rate of 0.73 young per pair per year.[53] In India, tawny eagles pairs seem to adapt to suboptimal overly sandy habitats by more dispersing nests, and can show similar productivity of chicks per nest as a result.[6] In Hwange National Park, 72.4% of pairs present were thought to breed on average in the course of a year, with an average of 0.61 fledglings produced per effort.[199] This is and other studies support that rainfall is key to productive success in tawny eagles of this area, with far more two egg clutches rather than one egg ones (which usually failed) and less confined breeding periods in years that had greater rainfall.[53][199] Breeding success, recorded as young per pair per year (ypy), was lower still in Namibia and Tsavo East National Park than in Zimbabwe (0.4, 0.5 and 0.78 ypy respectively).[53][108] Higher nesting success was found in Zambia, where pair produced a mean of 1 fledgling per nest.[108] Although an extensive study of lifespan are not known to have taken place for the tawny eagle, it is known that these eagles can live up to at least 16 years of age in the wild.[8][200]

An unusually light juvenile tawny eagle from India.

Status

Conservation

The tawny eagle still occupies a large range.

SABAP and SABAP2 in Southern Africa, occurring in only 323 of 1440 quarter degree grid cells.[201] During close study of the tawny and martial eagle in central Namibia, a precipitous decline was detected in both, with a tawny eagle population that was once regionally numbered about 19 pairs down to 2 known pairs.[202] The once seemingly innumerous population of this species within Kgalagadi Transfrontier Park was known by the 1990s to be down to merely 40 known pairs.[203] Roadside counts conducted in Mali, Niger and Burkina Faso show that although the majority of raptor species are in drastic population decline, only the tawny eagle and snake eagles are surviving outside of protected areas.[204] In India, the tawny eagle was once considered "our commonest eagle"[38] but strong declines have been detected with surveys indicating strongholds like Rajasthan have shown reductions of observed pairs by up to half.[6] According to the producer-scrounger foraging theory, vultures are to some extent reliant on tawny eagles to help locate carcasses.[158] Thus, the conservation of eagles outside protected areas is of vital importance to ensure the survival of vultures.[158]

Threats

A tawny eagle in the Serengeti.

Tawny eagles face a number of threats that affect their breeding behaviour, foraging success and ultimately the survival of individual birds. The most recent and devastating threat to survival occurred on 20 June 2019. The carcasses of 468 white-backed vultures, 17 white-headed vultures, 28 hooded vultures, 14 lappet-faced vultures and 10 cape vultures were found alongside 2 tawny eagles. A total of 537 vultures and 2 eagles were found poisoned in northern Botswana. It is suspected that they died after eating the carcasses of 3 elephants that were laced with poison by poachers. Carcasses are poisoned to ensure that scavengers are unable to aid rangers in the effort to locate poached wildlife. By circling above dead animals, large raptors act as an early detection system for anti-poaching rangers.[205][206][207][208] Poisoning events are far from restricted to Botswana and are thought to be a direct factor in the reduction of tawny eagles as well even in the protected areas of Kruger National Park.[209] In central Namibia, all 5 of the juvenile tawny eagles that were radio-tagged were poisoned by strychnine baits, completely decimating all recruitment of the species in the area.[202] Mysteriously, the populations of bateleurs and tawny eagles in the Maasai Mara appear to be bumping up as opposed to the declines reported elsewhere, seemingly in sync with the worsening declines of vultures on the Maasai.[210]

Further threats to tawny eagles include habitat loss and land-use changes such as intensified cattle grazing, firewood collection and sale and the charcoal industry.

global warming.[8][216][217][218][219] Also, clearly, the banning of poison baits and the mitigation of dangerous powerlines in eagle-utilized areas is key for the survival of the tawny eagles.[202][206][191]

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External links

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